FOOD SCIENCE - Scientific study of food from “farm to fork”.

• Or, more formally put:  Application of basic sciences (physics, chemistry and biology) and engineering to foods and the principles of food processing.

FOOD SCIENCE

• Multidisciplinary

• Foods as edible biochemicals

MORE PEOPLE, LESS FOOD

• Widespread food shortages will develop over the next 40 years as a population explosion gradually outstrips world food supply.

• The food supply is the most immediate constraint on the Earth’s population-carrying capacity.

• Milestones & Projections:

1830: World human population reaches 1 billion
1930: 2 billion
1960: 3 billion
1975: 4 billion
1999: 6 billion [Assuming a 64-year human life expectancy, of all the people   born on earth since its creation,
2/3 are now alive.]
2030: 9 billion
 
• Biggest increases are expected in some of the poorest areas, such as Africa, southern Asia, and South America.

Human population of Africa will double in 23 years.
Population of South America will double in 29 years.
Population of Europe will double in 343 years.
 
• Projection: Maximum amount of people earth can sustain = 20.7 billion.

1900s:

• Vacuum packaging - removes atmosphere from food packages.
• Hydrogenation - to keep unsaturated fats from turning rancid.
• U.S. & British patents issues for killing bacteria in food with ionizing radiation (1905).
• In U.S., first commercial freezing of fruit and fish.

1910s:

• In U.S., first large-scale commercial pasta production.

1920s:

• Clarence Birdseye develops quick-freezing process for foods and first commercializes blanched frozen vegetables.
• Food fortification begins by fortifying table salt with iodine (1924).

1930s:

• Freeze-drying process invented to preserve food.
• Vitamin D first added to milk through ultraviolet radiation (1933).

1940s:

• Mass production of food using automation takes off.
• Concentrated, frozen, and dehydrated foods produced in mass quantities for shipping overseas to military.
• Flour first fortified with vitamins and iron (1940).
• Aseptic processing and packaging is developed, increasing food quality, safety, and retention of nutrients.

1950s:

• Controlled-atmosphere packaging (CAP) developed (CAP controls O2 and CO2 in the package to limit respiration and ethylene production, thereby delaying ripening and spoilage).
• U.S. Army begins food irradiation program (1953).
•  Watson & Crick discover the double-helix structure of DNA, laying the foundation for understanding genetics and developing recombinant DNA technology.

1960s:

• First commercial plant for freeze-drying food opens (1960 - for coffee).
• Computer control in processing plants first introduced.
• FDA approves irradiation to disinfest wheat and wheat flour (1963), to inhibit sprouting in potatoes (1964), and to extend the shelflife of potatoes (1965).
• Aseptic canning adopted by food manufacturers.

1970s:

• Hazard Analysis Critical Control Point (HACCP) system jointly developed by NASA, Pillsbury Co., and the U.S. Army Natick Laboratories.
• Recombinant DNA technology developed (1973).

1980s:

• Modified-atmosphere packaging(MAP) introduced to increase shelflife and protect them from spoilage, oxidation, dehydration, weight loss, and freezer burn.
• FDA approves irradiation to control Trichinella spiralis in pork (1985), to disinfest and/or delay ripening in some fresh fruits and vegetables (1986), and to control microorganisms in spices and herbs (1986).

1990s:

• HACCP becomes widely adopted by food manufacturers largely due to regulations by FDA and USDA.
• FDA approves use of irradiation to control harmful bacteria in fresh and frozen poultry (1990) and red meats (1997).
• Pasteurization process for shell eggs by ohmic heating (using electricity).
• Flash pasteurization process of fresh juices commercially applied leading to not-from-concentrate citrus juices.
• Orange juice fortified with calcium.
• High-pressure processed guacamole comes to U.S. market (1998).
• Steam pasteurization and vacuuming of beef carcasses introduced to reduce microbial hazards.
• Recombinant enzyme, chymosin, replaces rennet in most cheese manufacture.
• First food from a transgenic plant (a tomato with delayed ripening) comes to market (1994).
• Active packaging systems introduced that interact with package contents or the package’s internal atmosphere are developed to enhance product freshness.

I.  Common operations used by the food industry in the making of food products.

II.  Materials handling - Harvesting and transportation while maintaining product quality to and in the processing plant.

• Low temperature storage to maintain perishable produce appearance and vitamin content.
• Volume restrictions due to “field heat” produced by fruits & vegetables.
• Care of handling livestock and fragile products such as eggs.
• Safety issues from static electricity buildup igniting sugar dust or fine flour transfer while avoiding humidity buildup and caking of product.
• Proper handling of spices to retain desirable aroma compounds.

III.  Cleaning - often required for the simple removal of dirt and debris.

A.  Brushes, high-velocity air, steam, water, vacuum, magnetic attraction of metal contaminants, mechanical separation, filtration, etc.

B.  Water treatment: In soft drinks, water should be low in inorganic salts, since these minimize carbon dioxide solubility and promote excessive escape of gas bubbles; often this requires additional treatment processes such as microfiltration and deaeration.

C.  Cleaning of food equipment surfaces

Moderately alkaline and neutral detergents find wide application in food industry as they remove soil and other deposits yet are noncorrosive to food-contact surfaces.

Many types and combinations of detergents used.

• Solid from a solid (e.g., shelling nuts; lye peeler for peaches)
• Solid from a liquid (e.g., filtration; centrifugation; crystallization of sugar crystals from sugar cane juice)
• Liquid from a solid (e.g., extracting juice from a fruit; pressing oil from peanuts and soybeans)
• Liquid from a liquid (e.g., centrifuging oil from water)
• Removing a gas from a liquid or solid (e.g., pulling a vacuum)

A.  Hand sorting and grading still very common (e.g., fruits & vegetables), but labor costs are high.

• Electronic photocell equipment used to detect and reject off-color products (e.g., potato chips, peanuts, eggs); ultrasonics also used to screen internal tissue of whole fruits and vegetables.

A.  Breakdown of large food particles into smaller particles.

• Examples: Cutting, grinding, pulping, homogenizing.
• Some cutting now done with high-pressure water jets and laser beams.

B.  Disintegration often involves heat build-up due to friction and some products require cooling (e.g., meats to avoid protein denaturation and coffee to avoid burned flavors).

Grinding of frozen meat is done to avoid this.

Or addition of dry ice that dissipates as carbon dioxide.

C.  Homogenization

A.  One of the most common operations in the food industry
• (both liquids and solids suspended in liquids)


B.  Many kinds of pumps  -  pump selected depends upon nature of food to be moved.
Rotary gear pumps have close tolerances among moving parts, chunk-type foods would be reduced to purees, and sometimes  this is the intent, so the pump serves two purposes.

A single-screw pump (with large clearances)  best for moving food with large pieces without disintegration (e.g., corn kernels, grapes, small shrimp).


C.  It is essential that all food pumps can be easily disassembled for thorough cleaning (stainless steel is the most common material used to make pumps for the food industry).

A.  Again, very common operation in the food industry; can be solid-solid, liquid-liquid, solid-liquid, gas-liquid, etc.

B.  Many are “kitchen-style” mixers, just bigger.
Most common used to mix solids into liquids to dissolve them is a propeller-type agitator within a stainless steel vat.

C.  Mixing usually involves the generation of heat and in foods it is often desirable to minimize this temperature rise by some form of cooling.

D.  Some mixing requires high rpm
Example: Mixer/beater found in ice cream freezers to incorporate air into ice cream mix to produce desired volume increase (overrun) required to attain desired texture.

A.  Reasons to heat:

Cook

Pasteurize

Preservation (e.g., blanching)

Drive off moisture (evaporate)

Develop flavors

Inactivate natural toxic substances (soybean meal)

B.  Need to control application of heat (often necessary to heat and rapidly cool the product)

• Rapid heating and cooling often require maximum contact of the food with the heating/cooling source (e.g., heat exchangers in the pasteurization of milk).
•  Steam-jacketed stainless steel kettle or tank often used for heating liquid foods (mixing propeller usually included to prevent scorching and even distribution of temperature).
• Canning - using a retort (pressure cooker)
• Roasting - circulating hot airC.  Cooling
• Again, a heat exchanger can be used, but with cold water pumped through the unit.
• Commercial blast freezers reach -26C
• Liquid nitrogen:  -196C

A.  To remove water, to recover desirable food volatiles, and to remove undesirable volatiles.

B.  Can be solar (raisins), heated kettle (water from a sugar syrup).

C.  Very common in the industry: Vacuum evaporation - reduced pressure allows liquids to boil at lower temperatures (the lower temperature causes less damage to food quality).

A.  Examples

Dried milk processed by spray drying (atomized liquid mixed with heated air); liquid foods are easiest to dry.

Mashed potatoes and tomato puree processed by drum drying (drum heated from within, applied layer of food flashes off its moisture on contact with heated drum, and thin film of food scraped off drum with long knives).

Peas and diced onions dried by moving through a long tunnel oven (subject of overheating and shrinkage), but a preferred method is,

vacuum freeze-drying (used for coffee),

food frozen, dehydrated under vacuum from the frozen state.

[This is a process of sublimation, the ice does not melt but under conditions of reduced pressure (high vacuum) goes off directly as water vapor.]

Application of pressure within an appropriate form.

Range of pressures used, varies considerably dependent upon the product.

For example: Extrusion

{Breakfast cereals - Extrusion cooking}

Formulated dough or mash is extruded under high pressure with heat.

To protect food from microbial contamination, physical dirt, insect invasion, light, moisture pickup or loss, flavor pickup or loss, and physical abuse (damage).

Containers include metal cans, glass and plastic bottles, paper and paperboard, plastic and metallic films, and combinations of these.

Packaging is automated.

Often such equipment is automated.

XV.  New processes

To increase the range of options within each unit operation, to improve quality or increase efficiency.

Examples include: supercritical fluid extraction, ohmic heating, and high hydrostatic pressure processing.

I.  In countries with an ample supply of food, consumers choose what they eat on the basis of quality = characteristics of acceptability.

Food quality detectable by our senses: appearance factors, textural factors, and flavor factors.

A.  Size and shape

Size: Easily measured (e.g., fruits and vegetables can be sized according to the openings they can pass through; the basis for automated separating and grading machines).

Shape: Some of the most difficult food engineering problems are the designing of equipment to pack odd-shaped food pieces.

B.  Color and gloss

Food color: Helps determine quality, ripeness and spoilage.

• Color and transparency/cloudiness: Can be measured with a spectrophotometer (measures light transmission through a liquid).
• Solids and liquids: Reflected color can be measured by comparison with defined colored chips.
• Hunter colorimeter: Color measurement by division into three components - value, hue and chroma.
• Value - lightness or darkness of the color.
• Hue - predominate wavelength reflected (which determines what the perceived color is).
• Chroma - intensity strength of the color.

[Color can be defined in terms based on these three components.]

Instruments available to measure shine or gloss.

C.  Consistency - viscosity; many types of viscometers to measure consistency.

Bostwick Consistometer - time it takes for food to flow down an inclined trough.

A.  Food qualities we feel.

B.  Food texture can be measured by resistance to force.

Squeezing (compression).

Shear (force applied so that one part of the food slides past the other).

Cutting.

Tensile strength (pulling apart). [Instron? used to measure these forces.]

[Chewing is actually a combination of forces.]

C.  Texture changes - do not remain constant in a food.

Change in water content plays a major role.

A.  Combination of both taste and smell and largely subjective and therefore difficult to measure, very complex.

Wide divergence of opinion.

B.  Color and texture influence flavor.

We become educated as to expect certain colors with certain flavors.

Greater intensity of color associated with greater flavor; same with greater viscosity to perception of greater flavor.

C.  Salt, sugar and acid can be measured using instrumentation.

D.  Taste panels
Analytical instruments can be used, but the human “test animal” is still the best.
Use of groups of people preferred over an individual opinion, as differences of opinion tend to average out.

1.  People involved in taste panels.

Trained people for specific products (e.g., butter and cheese).

Consumer preference groups - panels not specifically trained but provide insight as to what consumers prefer.

Highly trained people with heightened taste sensitivity and knowledge of what to recognize as attributes and defects.

2.  Environment for taste panels.

• Isolation of tasters to avoid influence by observing other tasters.
• Tasters unable to see how food was prepared or what its ‘identity’ is.

3.  Hedonic scale (for quality factors)

• Range from ‘dislike extremely to neutral to like extremely’.

4.  Approach

Preference test: Choosing one sample over another; samples are coded so that source or identity of food sample is unknown to taster.

Most common is the triangle test (a preference test):  Selecting the sample that differs from two others (total of 3 samples).

Usually no more than 5 samples tested at one sitting; sense of taste becomes dulled.  Statistical analysis of results is usually employed.

5.  In addition to flavor, taste panels judge texture, color, packaging, sample arrangement, etc.

A.  Nutritional quality

Chemical or instrumental analyses for specific nutrient; however, often animal feeding tests must be used, especially for quality of protein sources (biological value).

B.  Sanitary quality

Analysis for bacteria, yeasts, molds and insect fragments.

X-rays to detect physical contaminants (e.g., glass chips, stones, metal fragments).

C.  Keeping quality (storage stability)

Measured under storage and handling conditions to match conditions encountered in normal distribution.

Normal storage tests may take a year; extreme conditions may be used to speed things up.

A.  Types:

Research standards (for internal use by a company to maintain a competitive edge),

Trade standards (set up voluntarily by members of an industry to assure at least minimum acceptable quality), and

Government standards (many types), some are mandatory.

B.  Federal grade standards

Standards of quality administered by the USDA and FSIS (Food Safety and Inspection Service) for food inspection and grading.

Inspections are usually mandatory and assures product wholesomeness.

Grading voluntary and determines product quality (e.g., meats; meat grading established in the 1920s).

Also for eggs, fruits and vegetables (including canned product), nuts.

C.  Planned quality control

1.  Systematic control programs are essential.

• Requires constant monitoring/sampling and record-keeping.
• Ability to prevent and anticipate problems, as well as move quickly to correct them.

2.  Total quality management (TQM)

• TQM is a management system striving to continuously improve the quality of products by making small but incremental changes in a product’s ingredients, manufacture, handling or storage to result in overall improvement. [Adopted by the automobile industry.]

3.  Hazard analysis and critical control points (HACCP)

• HACCP is a preventative food safety sustem in which a process for manufacturing, storing and distributing a food product is carefully analyzed step-by-step; goal is to eliminate a problem before it occurs.

I.  Food deterioration includes declines in organoleptic desirability/aesthetic appeal, nutritional value, and safety (i.e., product quality); occurs under the best of conditions.

II.  Factors adversely affecting food:

Changes in temperature (heat and cold),
light and other radiation,
oxygen,
changes in moisture content (water loss or uptake),
detrimental enzymes of the food,
microorganisms and macroorganisms,
industrial contaminants (e.g., packaging materials) and close proximity of other foods, and
time.
[Factors commonly act in combination.]

IV.  Shelf-life and dating of foods

A.  Definition of shelf-life:  The time it takes for a product to deteriorate to an unacceptable level (what is unacceptable is sometimes a matter of opinion).

B.  A better definition:  Length of time a product remains salable.
It is common for a food manufacturer to define a minimum acceptable quality (MAQ) for a product.

C.  Actual length of shelf-life dependent on:

processing method,
packaging, and
storage conditions.

D.  Dating system

1.  Different code dates:

Date of manufacture (pack date),
Date the product was displayed (display date),
Date by which the product should be sold (sell by date),
Last date of maximal quality (use by date), and
Date beyond which the product is no longer acceptable (use by date or expiration date).

2.  Use of these code dates requires a need to predict and monitor shelf-life.

Models for predicting shelf-life are particularly useful for new products without a distribution history.

A.  Microorganisms (bacteria, yeasts and molds)

More types of microorganisms can spoil food than cause foodborne disease.
Sources of these microorganisms:  soil, water, air, food itself, humans, food equipment environment.
*Healthy living tissue (internally) is usually sterile, hence the presence of spoilage organisms is mostly the result of contamination.
Bacterial endospores are most difficult to inactivate.
Heat and moisture will increase growth and activities of microorganisms.
Molds as compared to bacteria can generally grow at:
lower pH (more acid conditions),
lower moisture contents (dryer conditions),
higher salt concentrations, and
lower temperatures (in refrigerated foods).
Molds usually only a problem with spoilage, not safety, but Aspergillus flavus and Aspergillus parasiticus produce aflatoxins which are potent hepatocarcinogens.
*Molds require oxygen for growth.

 B.  Insects and rodents

Insects destroy 5 to 10% of U.S. grain crop annually (in other parts of the world it can reach 50%); insects damage crops so that spoilage microorganisms are more of a problem.
[Some commodities have allowable levels for insect parts as it is recognized that these foods cannot be produced without some contamination.]
Rodents both consume and contaminate food; control is critical since mice and rats can reproduce very quickly; rodents can spread disease.
Food enzymes
Enzymes inherent in food continue to function after death of animal or plant; some enzymatic activities can be accelerated following death.
Can be controlled by refrigeration or blanching.

C.  Heat and cold - can cause deterioration of food if not controlled.

Excessive heat denatures proteins, breaks emulsions, dries out foods, and destroys vitamins.
Uncontrolled cold will damage fruits & vegetables if allowed to freeze resulting in discoloration, and texture changes; freezing milk will break its emulsion and casein will curdle; bananas, lemons, squash and tomatoes are subject to “chill injury” at <10C.

D.  Moisture and dryness

Excessive moisture can lead to undesirable microbial growth.
Surface moisture from high relative humidity can cause lumping, caking, browning, crystallization, and stickiness.
High moisture-barrier films can trap moisture from respiration and transpiration in fruits & vegetables.
In nonrespiring foods in a moisture-barrier package can give up moisture, changing the relative humidity of the package headspace and with a drop of temperature, condensation in the package occurs.
 Excessive drying leads to undesirable texture changes and appearance.

E.  Oxygen

1.  A very highly reactive element of the atmosphere.
2.  Molds and aerobic bacteria require oxygen for growth so vacuum packaging or modified-atmosphere packaging (MAP) works well against these spoilage organisms.

F.  Light

1.  Visible light is a source of energy.
2.  Inactivates some vitamins and causes deterioration of many food colors and flavors.
3.  Opaque packaging will protect light-sensitive foods.

G.  Time

1.  Peak time for quality is usually immediately or soon after harvest, slaughter or manufacture.
2.  Exceptions are those foods aged/fermented, such as cheeses and wines.

A.  Keep food alive as long as possible.

B.  If food must be killed (e.g., for meat) -- clean it, cover it, and cool it as quickly as possible.

Keeping the food alive as long as possible if often not feasible, and deterioration of perishable foods can only be delayed a short time.

A.  Most important means of controlling microorganisms:

Heat
Cold
Drying
Acid
Sugar
Smoke
Atmospheric composition
Chemicals
Radiation

A.  Enzymes probably the second greatest cause for food spoilage.

B.  Many of same principles for food preservation apply for enzymes as for microorganisms.

For example, when a food is pasteurized, enzymes are denatured and thus rendered inactive.
When a food is refrigerated to slow down the growth of microorganisms, so is the activity of enzymes slowed down.

C.  However, some food enzymes may be more resistant to preservation effects than microorganisms; for example, as in food irradiation where enzymes are only slightly affected.

Sample Questions taken from last year's first exam:

Multiple choice questions

Food science is:

1. the holistic study of foods and beverages using the principles of molecular genetics, chemical engineering, and quantum mechanics.
2. the US government method of meal service in which all of the food is placed in packaging containing containers on the table followed by distribution and consumption.
3. the application of basic sciences (i.e., physics, chemistry, and biology) and engineering to foods in combination with the principles of food processing.
4. food product development by combination of the disciplines of human nutrition and food service.
5. the study of the microbial ecology of foods with emphasis on the effect of the environment on food spoilage, as well as the physical and chemical destruction of microorganisms in foods.

The foodborne molds, Aspergillus flavus and Aspergillus parasiticus, are notable because they are:

1. capable of growing in atmospheres containing oxygen.
2. as thermophilic as Bacillus and Clostridium.
3. capable of surviving milk pasteurization.
4. the most toxic of all fungi.
5. unable to grow unless exposed to sunlight.

Examples of commercial food products normally dried using a drum dryer include:

1. ground black pepper and cottage cheese.
2. tomato puree and instant mashed potatoes.
3. dehydrated peas and diced carrots.
4. breakfast cereals such as Frosted Flakes and Cheerios.
5. nonfat dry milk and instant coffee.

In the food industry, the last new product wave peaked in 1995; that product wave was:

1. probiotic culture-supplemented dairy products.
2. low- and non-alcoholic beers and wines.
3. flash pasteurized citrus juices amended with elevated levels of antioxidants and minerals.
4. chocolate-covered, double-stuffed Oreos.
5. low-fat and no-fat products.

Nicolas Appert's invention of a food preservation system from which the technology of canned foods evolved was awarded a prize in 1809 by:

1. the Marquis de Lafayette
2. Thomas Jefferson
3. Marie Curie
4. Peter the Great of Russia
5. Napoleon

Which of the following is not considered a food industry unit operation?

1. cleaning
2. materials handling
3. forming
4. evaporation
5. sale of the product

True/False questions

The most immediate constraint on the Earth's human population-carrying capacity is the world supply of medicines and drugs, especially antibiotics.

Stainless steel is the most common material used to make pumps for the food industry.

Homogenization increases the size of the larger fat globules in milk and thus prevents the globules from migrating through the skim portion of the milk.

The first US and British patents for use of irradiation in the killing of bacteria in foods (i.e., food preservation) were recently awarded in 1995.

There are more kinds of microorganisms that can spoil food than can cause human foodborne disease.

Color and texture do not influence flavor.

In the manufacture of some food products, X-rays are used to detect physical contaminents such as metal fragments, stones, and glass chips.

HEAT PRESERVATION AND PROCESSING (Ch. 8)

I.  An integral part of food preparation in a variety of forms, including cooking; cooking is often the last treatment a food receives before serving.

II.  Degrees of preservation

A.  Sterilization - complete destruction of all microorganisms; because of the extreme heat resistance of bacterial endospores, a treatment of 121?C (250?F) of wet heat for 15 min is required (every part of the food must receive this treatment).
[Many foods need not be “completely sterile” to be safe and have keeping quality.]

B.  Commercially sterile - all pathogenic and toxin-producing organisms have been destoyed, as well as other types of organisms that can spoil the product when held under normal storage conditions (e.g., canned foods may contain a few thermophilic spores; unless the cans are held at very warm temperatures, there will be no spoilage).

C.  Pasteurization - usually treatment is below the boiling point of water and dependent upon type of product.

For milk and liquid eggs it is specifically designed to destroy pathogens associated with the food having public health significance.
For more general use as with beer, wine and fruit juices, it is designed to extend product shelf-life from a microbial and enzymatic aspects.
[For apple juice and E. coli 0157:H7, such is not the case.]
[Pasteurized products normally require additional means of preservation, e.g., the refrigeration of milk.]
D.  Blanching - a type of pasteurization usually applied to fruits and vegetables to inactivate food enzymes.

How do processors choose the optimal heat reatment for a particular food?
Time-temperature combination required to inactivate most heat-resistant pathogens and spoilage organisms in a particular food.
Heat-penetration characteristics in a particular food in a particular container.

A.  Most heat-resistant pathogen is Clostridium botulinum.

 B.  Most heat-resistant (nonpathogenic) spoilage microorganisms are Bacillus stearothermophilus and Clostridium thermosaccharolyticum.

C.  Thermal death curves

When bacteria are killed by heat, the death rate is linear (first-order, or a logarithmic order of death).
D value = time in minutes at a specified temperature necessary to kill 90% (l log10 cycle) of the bacterial population (either vegetative cells or spores).
z value = the number of degrees (temperature) required for a specific thermal death time curve to pass through one log cycle of D values.
Different organisms in a different food will have different z values in different foods.
z values characterize resistance of the populations to changing temperature.
F value = the number of minutes at a specific temperature required to destroy a specified number of organisms having a specific z value.
F value is a measure of the capacity of a heat treatment to sterilize.
F0 value is a reference value designating the time at 121?C (250?F) required to destroy a specific number of organisms whose z value is 10?C (18?F) which is the z value for Clostridium botulinum.

D.  Margin of safety

12D kill = heat process capable of killing 1012 spores of heat-resistant C. botulinum in a food with pH greater than 4.6.

A.  How does one ensure that every particle or portion of feed (within the can) received the required heat treatment?
This is a problem of heat transfer (or heat penetration into the coldest spot of the food in the can).

B.  Conduction and convection heating in canning

In conduction, heat move from one (solid) particle to another by contact, in relatively straight lines (the food does not move in the can and there is no mixing of hot food with cold).
Convection heating in a can takes far less time due to mixing of hot fluid food closest to the heat source with colder internal fluid portions (mixing is also promoted mechanically by can movement).
Pieces of food in liquid are intermediate in time of heating due to shared characteristics of conduction and convection.

C.  Cold point in food masses - area in a can or mass of food that is last to reach the final heating temperature.

In can of solid food heated by conduction the cold point is located in the very center of the can.
In foods undergoing convection heating (unless the cans are agitated), the cold point is somewhat below the dead center of the can.

D.  Determining process time and process lethality

 Use of heat-sensing thermocouples placed at the cold spots in the can; these measure come-up times for the heat process inside the can as well as the cooling periods.
Total lethality of the heat process represents a summation of the lethal effects of changing temperatures with time during the entire retort operation.
The required heat treatment will be different depending on the retort, the size and shape of the containers, and the composition of the food.

Several constituents of foods protect microorganisms against heat:
Sugar, starch and proteins in high concentrations.
Fats and oils interfere with the penetration of wet heat.
Different compositions of container have different degrees of heat transfer.

Method: A substantial population of  clostridial strain PA 3679 is inoculated into cans of food that are then processed in a retort.
After processing, the cans are stored at temperatures favorable for outgrowth of any surviving spores, and checked periodically for growth and spoilage, such as bulging cans due to gas production.

A.  Different combinations can vary greatly in their damaging effect on foods; the shorter the thermal processing time the better the organoleptic quality of the food.

B.  The higher the temperature the greater the rate of kill of microorganisms.

C.  Therefore, high temperature/short time is preferred to low temperature/long time in thermal processing.

Originally the beverage industry used 62.8?C for 30 min to pasteurize juice, now flash pasteurization at 121?C for 2 sec is common practice using tubular-scraped surface-type heat exchangers.

A.  Examples.

1.  Still retort - one of the simplest applications of heating foods in containers (works best with solid foods).
Essentially this is use of a larger, batch-style pressure cooker with no agitation, but this method oftens results in overheating of food.
2.  Agitating retort -  “pressure-cooking with movement”
Processing time shortened and food quality improved, especially with liquid or semiliquid foods.
Free headspace in can necessary for optimum food turnover within the can.
3.  Pressure considerations
 High temperatures required for commercial sterilization normally obtained by using steam under pressure (15 pounds/in2 = 121?C).
Containers need to withstand the rigors of retorting, such as pressures, temperature changes, contact with other containers.
4.  Hydrostatic cooker and cooler (Fig. 8.10)
“U” tube: Legs are sufficiently tall enough to produce a hydrostatic head pressure to balnace the steam pressure in the sterilizing zone.
5.  Direct flame sterilization
Cans pass directly through gas jets; heating rates are excellent, but difficult to control on a consistent basis.
6.  In-package pasteurization
Hot water sprays or steam jets directed at the containers in varying temperature zones.
Temperature changes must be gradual to prevent thermal shock to glass (as with pasteurization of beer bottles).

B.  Heating food prior to packaging

1.  Advantage:  Can heat food more rapidly out of a container than in it.
2.  Batch pasteurization  - used in some parts of the world for milk, but this method requires a holding time (30 min at 62.8?C to kill Coxiella).
3.  High-temperature/short-time (HTST) pasteurization
Held at least 71.7?C for 15 sec.
Continuous process; raw milk held in a cool storage tank is pumped through a heat exchanger and cooled again.
Widely used in the food industry.
4.  Aseptic packaging
Food commercially sterilized outside of containers (usually continuously) and then placed in previously sterilized containers.
Packaging containers normally utilize papers and plastic materials that are sterilized, formed, filled, and sealed in a continuous operation.
Packages sterilized using hydrogen peroxide in combination with heated air or ultraviolet (UV) light.
Quick heating of liquid foods can be done in a plate-type heat exchanger or in a tubular scraped-surface heat exchanger (Fig. 8.12;  a tube within a tube capable of sterilizing a food within 1 or 2 sec).  [Also called ultrahigh-temperature (UHT) sterilization.]
Sterile food must be quickly cooled to room temperature using heat exchangers using refrigerants instead of steam.
This technology has been developed for volumes as large as silo tanks and railroad tank cars.
5.  Hot pack or Hot fill
Packing of previously pasteurized or sterilized foods while hot into clean but not necessarily sterile containers.
Most effective with acid foods (pH <4.6).
6.  Microwave heating - eliminates temperature gradients as far as microwaves can penetrate food resulting in rapid heating.

A.  FDA requires Good Manufacturing Practices (GMPs) be followed to help assure food safety and wholesomeness.

1.  Includes specific safe regulations for low-acid canned foods.
Foods thermally processed, pH >4.6, water activity >0.85, packaged in hermetically sealed containers, and not stored under refrigeration.
2.  Also regulations for acidified foods.

Microwave heating (pp. 256-261)

I.  Heating with low-energy radiation

A. Microwaves are electromagnetic waves of radiant energy, differing from light and radio waves only in wavelength and frequency.

B.  Wavelengths of 0.025 to 0.75 m

C. FCC-approved frequencies are between 2450 and 915 MHz for food use, otherwise may interfere with communication processes.

D.  Microwaves travel in straight lines but are reflected by metals, pass through air and most glass, paper and plastics.

E.  Are absorbed by food constituents, especially water.  Loss factor is the microwave energy lost in passing through materials or being entirely absorbed by materials; materials highly absorbent of microwaves are called lossy; highly lossy materials are heated rapidly.

F.  Foods vary in microwave heating patterns; the more heat produced, the shorter the distance microwaves can penetrate before losing all energy.

II.  Mechanisms of heating

A.  Water molecules are polar; when microwaves pass into a food, they orient the water molecules in the direction of the electric field; when the electric field reverses as 915 or 2450 million times per second intermolecular friction generates heat. 

B.  As heat is generated at the sites of billions of molecules, it is also conducted among food components tending to equalize the temperature.

III. Differences

A.  In conventional heating, heat source causes food molecules to react largely from the surface inward, so that a temperature gradient is formed; microwaves penetrate 1 to 2 inches; in this area heat is generated quickly and relatively uniformly.

B.  There is an internal boiling away of moisture; the steam heats adjacent food by conduction; as long as moisture present the temperature does not raise above the boiling point of water; there is no surface browning.

IV.  Microwave ovens have a magnetron = microwave generator = electron tube within a magnetic field which propagates high-frequency radiant energy.

A.  Industrial microwaves are complex microwave tunnel ovens equipped with a moving belt of low-loss materials on which food is conveyed past the magnetrons in a continuous fashion.

B.  To heat liquid materials continuously with microwaves, the liquid is pumped through low-loss glass tube and the magnetrons can be positioned around the tube in which liquid is pumped; microwaves used by the industry for many applications requiring heat, but the choice of method of heating is usually dependent upon the product quality and cost.

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Ohmic heating (pg. 262)

I.  Advantages of continous ohmic heating is that less heat damage to product occurs, it is a more efficient operation (higher through-put), and can be coupled with aseptic packaging systems.

II.  Heat generated when an alternating electric current is passed through a conducting solution (water the major component); in ohmic heating a low-frequency alternating current of 50-60 Hz is combined with special electrodes; product passed continuously between the electrodes, usually a series of electrodes that raise the temperature of the food quickly; the solid pieces and liquid are heated almost simultaneously; continuous heat exchangers used to cool the food quickly.

III.  Problems with scorching/fouling of electrodes; particulates/solid pieces still pose a problem depending on size and conductivity; issues of cost, and safety concerns with low-acid, particulate foods.

I.  Types: Irradiation, oscillating magnetic fields, ultrasound, intense light pulses, pulsed electric fields & high hydrostatic pressure.

II.  Benefits: Maintain sensory and nutrient qualities closer to raw or fresh (e.g., aroma and flavor, color and overall appearance, texture, nutrient content), and create new or different product types.

III.  Commercial challenges: Economic reality, perceived value by consumer, product safety, and product shelf-life.

IV.  Food safety - Pathogens versus minimal and nonthermal novel processes: Emerging (“new”) global pathogens including protozoans, invertebrate parasites, and viruses; pathogens with greater resistances to antibiotics as well as increased virulence; stress-induced resistances (adaptation by pathogens) to new combinations of food processing and food preservation methods.

V.  Hurdle concept: Involves the application of multiple preservation factors to prevent the growth of pathogens and spoilage organisms.  [Instead of a single treatment (such as heat), a combination approach of processing techniques allows improved retention of sensory attributes and nutrient content of the food.]

VI.  Irradiation: Has general use applicability; Has substantial benefit to control insects and nematodes as a replacement for chemical fumigation (e.g., fresh fruits and vegetables of quarantine importance); to replace the chemical fumigants - methyl bromide, ethylene dibromide, and ethylene oxide.

VII.  Factors affecting consumer acceptance of irradiation: The psychological barrier; increased awareness of food safety issues and growing pressure from consumers to eliminate all pathogens present in our foods (e.g., E. coli 0157:H7 in ground beef); cost of implementation.

VIII.  Ultrasound:  Use of sonic waves to inactivate microorganisms in foods, but sonic waves not powerful enough to kill microorganisms or inactivate enzymes; ultrasound used to scan/visualize internal components of food, but power limitations prevent its use as a preservative method.

IX.  Oscillating magnetic fields (OMF): Has potential to pasteurize a food; as with ultrasound,
OMF has “power problems”, there are product-thickness limitations; no effect against enzymes and spores.

X.  High-intensity pulsed light: Rapid, intense, magnified flash of light or electrical energy from a capacitor; 20,000X the intensity of light; significant reduction of spores and vegetative microorganisms; irregular surfaces (e.g., shadows) a problem; cost analysis favorable for commercial use.

XI.  High-intensity pulsed electric fields: Extremely short burst of high voltage into food; best suited for fluid foods that can be effectively cooled as it flows continuously between two treatment electrodes (uncooled, it is essentially ohmic heating); microbial reductions can be significant; cost analysis favorable for commercial development, but scorching remains a problem.

XII.  Applications of high hydrostatic pressure processing (HPP) in foods: Pasteurization and sterilization; protein modification (e.g., meat tenderization and formation of protein gels); phase transition changes (e.g., starch gelatinization to soften legumes and grains, reversible decrease in melting point of ice, reversible increase in melting point of lipids).

XIII.  HPP Applications (continued): Gas removal or solubilization with carbon dioxide; extraction of constituents from foods (such as pectin); powder agglomeration (e.g., for the production of food bars or cubes); surface impregnation or coating of foods (e.g., adsorption of minerals and vitamins).

XIV.  HPP is a batch (for packaged foods) or semi-batch (for pumpable foods) process; pressure chamber must be securely enclosed to reach high pressures, so a continous process is not possible.

XV.  Use of HPP to treat foods is not new.  Bert Hite at West Virginia University first published on pressure treatment of foods for preservation purposes back in 1899.  The machine he built could attain pressures of 135,000 psi.

XVI.  The first HPP food to come to the marketplace was a fruit jam sold in Japan in 1991; fruits fit well with HPP since the low pH of fruits and fruit products prevent outgrowth of bacterial endospores; use of HPP alone will not eliminate spores in a food, a hurdle approach is required.

XVII.  HPP will denature proteins in meats, poultry and seafood and this change in appearance is easily seen; the higher the magnitude of pressure the greater the degree of protein denaturation; egg white (ovalbumin) denatured using pressure has the same appearance as egg white denatured by heat, but the texture and mouthfeel is significantly different.

 XVIII.  HPP foods will brown in polyphenol oxidases and other browning enzymes are not inactivated; this requires blanching of some products; in some cases (as with pears), pressure will accelerate enzymatic browning.

XIX.  HPP will inactivate vegetative forms of bacteria, yeasts, molds and viruses; the greater the magnitude of pressure and the longer the treatment, the greater the extent of microbial kill (in most cases).

XX.  HPP characteristics:  The initial and final treatment temperatures will be the same, but during pressure treatment, there is adiabatic heating (heat of compression), this heat enhances microbial kill; there is no product shear (no homogenization); there is uniform treatment by pressure (it is sample size independent);

___________

Videotape of food irradiation.

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Cold Preservation and Processing (Ch. 9)

I.  History

A.  Freezing and refrigeration among the oldest methods to preserve food.

B.  Mechanical ammonia refrigeration systems for food preservation developed in 1875.

C. In 1920s, Clarence Birdseye pioneered work in the production of frozen foods.

D.  Mechanical refrigeration in transient makes world trade of perishable food commodities possible.

A.  Cool storage (refrigeration): Usually from about 16?C to about -2?C (most commercial and household refrigerators between 4.5 to 7?C).

Most foods do not freeze until about -2?C or lower.

B.  Good frozen storage requires -18?C or lower.

A.  The “gentlest methods” of food preservation, but works well with perishable foods for only a short time period.

At 0?C, the shelf-life of perishable foods is usually <2 weeks.
At 5.5?C (more realistic temp. for home refrigerators), the shelf-life is often <1 week.
At 22?C (~room temp.) these foods may spoil in a day or less.

B.  Ideally, refrigeration is continuous from harvest/slaughter until consumer purchase.

 Most metabolically active fruits & vegetables require refrigeration to remove “field heat” and slow down metabolism.

C.  Principle requirements for effectiveness of refrigerated storage

1.  Low temperature

Refrigerated storage rooms require sufficient refrigeration capacity and insulation to maintain temp. ±1?C.
# of doors and factors causing the generation of heat are important.
Different fruits & vegetables generate different levels of heat.

2.  Air circulation and humidity control

Air circulation required to move heat away from food surface.
Air too moist, surface condensation and mold growth are possible; air too dry, and foods will dry out.
Each food has a characteristic optimal temperature and relative humidity (RH) for storage; usually the best RH is equivalent to the moisture content of the food itself.
Packaging can be used to lessen transfer of water into or out of a food for prolonged storage periods.

3.  Modification of gaseous atmospheres

Controlled atmosphere (CA) storage - modification of storage or packaging atmosphere by vacuum, addition of nitrogen or CO2, or any departure from composition of air.
Warehouses/truck trailers
Packages
Example:  McIntosh apples are stored at 3?C, 87% RH and an atmosphere of 3% oxygen & 3% CO2 for 1 month, then 5% CO2 (nitrogen makes up the balances). [On the other hand, Delicious apples prefer storage at 0?C.]
Hypobaric storage - refrigerated storage under reduced pressure and high RH (reduced pressure lowers oxygen levels and high RH prevents product dehydration).
Such specialized storage conditions must be cost effective.

A.  Freezing was a major factor in bringing convenience foods to the home and restaurant; freezing offers maximal convenience and (if properly done) minimal quality changes to the food.

B.  Initial freezing point

1.  Increasing the solute concentration of a solution lowers its freezing point.
2.  Thus different foods will freeze at different temperature and different rates (heat transfer out of the food).
3.  Food does not freeze uniformly (e.g., “water component” of food freezes first and then the more concentrated solutions (higher and higher in dissolved solids).

C.  Changes during freezing

1.  Concentration effects

For best quality, most foods must be solidly frozen, otherwise may get:
lactose crystallization
broken fat emulsions
concentrated salts can denature proteins

2.  Ice crystal damage

 When water freezes slowly, large ice crystals form (and small crystals coalesce to create larger ones) that cause physical rupture and separation of cells in food tissue.
Large ice crystals can also destabilize emulsions.

D.  Rate of freezing - fast freezing is required for high quality.

The smaller the size of the ice crystal, the better.
Fast freezing minimizes concentration effects by decreasing the time concentrated solutes are in contact with food tissues.
Commercial freezers designed for rapid freezing; plate freezers and liquid-nitrogen freezers are very efficient.
Home freezers usually have the slowest freezing rates.

E.  Final temperature

1.  The factors affecting the choice of final temperature of freezing are
textural changes, enzymatic and nonenzymatic chemical reactions, microbiological changes, and costs.
2.  These factors dictates an internal temperature of -18?C (0?F) or lower and kept there throughout transport and storage; costs generally makes transport and storage temperatures below -30?C impractical.
3.  A temperature of -18?C is well below the lowest growth temperature for pathogens (3.3?C) and spoilage organisms (-9.5?C).
4.  Some enzymes retain activity down to -73?C, but reaction rates are extremely slow; -18?C usually works well although for fruits and vegetables, blanching may be done to inactivate stubborn enzymes prior to freezing.
5.  Frozen fish not very stable; at temperatures of -9 to -7?C, quality may be retained for only days or weeks (depending on the product).
6.  Most refrigerated trucks for transportation of frozen foods are not capable of holding -18?C.
7.  Supermarket display cases are usually above -18?C near the top, but may be colder below.

F.  Damage from intermittent thawing

1.  Repeated freezing and thawing cycles are very detrimental to stored foods.
2.  Complete thawing not necessary to cause damage.
3.  All commercial freezers have a measurable temperature cycle; cycles are part of the control system.
Not uncommon for a frozen storage chamber to go from its maximum to its minimum and back again on a 2-h cycle.
4.  A 3?C fluctuation above and below -18?C can be damaging to many foods.
At -12?C thawing intensifies the concentration effect; upon refreezing, water melted from small ice crystals tends to bathe unmelted crystals, causing them to grow.
5.  In the thawing of frozen foods, if thawing is slow, quality can again suffer.
Eutectic mixture - is a solution of such composition that it freezes (or thaws) as a complete mixture, rather than becoming more concentrated due to further separation of pure ice.
Eutectic temperature (or eutectic point) - the temperature at which a eutectic mixture is formed.
 For example, a dilute solution of NaCl in water will first freeze out pure water concentrating the NaCl.  At -21?C, the mixture of 23% NaCl and 77% water will freeze solid.
If thawing is slow, food components have more time to be in contact with concentrated eutectic mixtures (which is not good).

A.  Product’s refrigeration load = the quantity of heat that must be removed to reduce the temperature of the product from its initial temperature to the temperature consistent with good frozen food storage.

B.  Load made up of three parts:

1.  Heat removed to cool the food from its initial temperature to its freezing point.
2.  Cause a state of change at the freezing point.
3.  Lower the temperature of the frozen product to the specified storage temperature.
Can be calculated in calories, joules or British Thermal Units (BTUs)

C.  Heat

1.  Different substances can absorb different amounts of heat = different heat capacities.
2.  Specific heat = ratio of heat capacity to that of water.
3.  Two types of heat:sensible heat and latent heat.
a.  Sensible heat is readily perceived by the sense of touch.
b.  Latent heat is the quantity of heat required to change the state or condition which a substance exists.
4.  The specific and latent heats of foods are used to determine refrigeration requirements for cooling, freezing, and storage.

D.  Factors determining freezing rate = the driving force divided by the sum of resistances to heat transfer.
Driving force is the temperature difference between the product and the cooling medium.

E.  Resistances that are dependent upon:

1.  Air velocity (greater the velocity or degree of mixing, the greater the degree of heat transfer).
2.  Thickness of product.
3.  Resistance to heat transfer of the food package - different packaging materials have different degrees of resistance to heat transfer.
4.  Geometry/design of system

Degree of contact of cooling medium with food.
Extent of agitation.
Counter-current or same direction circulation of food and cooling medium

5.  Composition of the product

Food components have different thermal conductivities that change with temperature.
The greater the conductivity, the greater the cooling and freezing rates.
 In the cooling and freezing temperature range, heat conductivities change little until the phase change from water to ice occurs.
Since the thermal conductivity of ice is far greater than that of water, the thermal conductivity of food increases rapidly as it passes from the unfrozen to the frozen state.
[Rates of cooling and freezing are not constant since thermal conductivities change as water changes to ice.]
Fat and air have much lower thermal conductivities than water, therefore high levels of fat or entrapped air reduce the freezing rate.
An example showing how the physical structure of food influences freezing rates.
If two food systems both contain 50% water and 50% fat; it does matter if it’s an oil-in-water emulsion or a water-in-oil emulsion (i.e., which one is the continuous phase).
[The oil-in-water emulsion (water is the continuous phase)  should have a greater thermal conductivity (should freeze at a faster rate) than the corresponding water-in-oil emulsion (oil is the continuous phase) of the same chemical composition.]

F.  So in summary, the basic principles of freezing are:

1.  Greater the temperature difference between food and refrigerant, the faster the freezing rate.
2.  Thinner the food piece or greater the heat transfer rate of the food package, the faster the freezing rate.
3.  Greater the velocity of refrigerated air or circulating refrigerant, the faster the freezing rate.
4.  More intimate the contact between food and cooling medium, the faster the freezing rate.
5.  Greater the refrigerating effect or heat capacity of the refrigerant, the faster the freezing rate.

G.  Examples of how substantial major variables on freezing rate can be.

1.  Lowering air temperature in a tunnel-type freezer from -18 to  -30?C can shorten freezing time of small cakes from 40 min to ~20 min.
Spraying cakes with liquid nitrogen (at -196?C) cuts freezing time to <2 min.
2.  Small fish fillets or individual fruits will freeze in 3 h in still air at -18?C, but increasing air velocity to 250 ft/min (1.25 m/sec) will decrease freezing time to ~1 h.
Increasing air velocity further to 1,000 ft/min (5 m/sec) will drop the freezing time to about 40 min.
[These variables do not affect freezing rate in a linearly.]

A.  Freezing in air - Cold air with various degrees of velocity.

1.  Types include:

a.  Still-air “sharp” freezing to high-velocity blast freezer tunnels.
b.  Fluidized-bed freezing: Placement of high-velocity nozzles underneath food on conveyor belt or tray whereby small food portions are subdivided and moved by cold air.

2.  Oldest and least expensive air freezing method (equipment-wise) is still-air sharp freezing.

a.  Food placed in cold, insulated room usually of -23 to -30?C.
b.  Originated in 1860.
c.  Air circulation is mild (i.e., slow convection current).

3.  Blast-air freezing operate at -30 to -45?C with forced air velocities of 2,000-3,000 ft/min (10-15 m/sec).

a.  In comparison, a 30-pound container of eggs can take 72 h
to be frozen in a sharp freezer, but 12-18 h in a blast freezer.
b.  Blast freezers range from rooms to tunnels (with conveyor belts or cart racks moving food through).
c.  Design can be horizonal or vertical.
d.  IQF = individual quick frozen (food frozen individually, usually with fluidized bed freezing, clusters are disaggregated, and food packaged under cold air, such as shrimp or peas).
e.  Counter-current air flow often used: Coldest air first contacts already frozen food as it leaves freezer; this makes freezing progressive.
f.  Freezer burn and high-velocity blast freezers:

Unwrapped food in cold blast zone will lose moisture (whether in process of freezing or already frozen) that results in frosting over of refrigerated coils or plates requiring   defrosting, or freezer burn.
Freezer burn = sublimation or a form of freeze-drying; producing undesirable food surfaces, nutrient loss, and other defects.

To minimize freezer burn:

Method One - Food is prechilled (with high-humidity air at ~ -4?C), thus partially frozen food undergoes minimum moisture loss; then prechilled food is quickly finish-frozen allowing only minimum time for food to lose more moisture.
Method Two - Wet unpackaged food pieces prechilled to freeze a thin ice glaze around each piece; then glazed food quickly finish-frozen, the glaze protecting underlying food from freezer burn.
[Packaged frozen foods minimize freezer burn and frosted coils.]

B.  Freezing by indirect contact with the refrigerant.

1.  Food or food package is in contact with a surface (e.g., plates, trays, belts, or other cold walls) that is cooled by a refrigerant, but there is no direct contact between food and refrigerant.
2.  Example: Liquid foods and purees that are pumped through a cold wall heat exchanger and frozen to a slush condition, and preformed hamburger patties.
3.  Efficiency is dependent on the degree of contact between the plates and food (e.g., small air spaces will slow rate of freezing).
4.  Tubular scraped-surface heat exchangers used (see Fig.  8.12), with refrigerant rather than steam on the side of the wall  opposite the food; normally frozen to a slush then pumped to a package, sealed, and hard-frozen in an blast or immersion-type freezer.

C.  Freezing by direct immersion in a refrigerating medium.

1.  Done by submerging the food or spraying cold liquid onto the food or package surface, resulting in:

a.  intimate contact and effective heat transfer (good for irregularly shaped foods, e.g., mushrooms and shrimp),
b.  minimum contact with air which is desirable for foods sensitive to oxidation,
c.  high-speed freezing and extremely high quality.

2.  Refrigerants must be nontoxic, pure, clean, and free from foreign tastes, odors, colors or bleaching agents; for packaged foods, the package should not be damaged.

3.  Two types of immersion refrigerants are:

 a.  Low-freezing-point liquids, such as solutions of sugars, NaCl, and glycerol.

Must be used at a sufficient concentration to stay liquid at -18?C or lower; 23% brine can reach -21?C (which is used for freezing fish at sea).
These are chilled by indirect contact with another refrigerant.
Immersion freezing is usually limited to packaged foods due to problems of undesirable flavor transfer or other sensory issues.

b.  Cryogenic liquids, such as compressed liquid nitrogen and liquid carbon dioxide (-79?C).

Liquid nitrogen preferred because of its extremely low temperature, nontoxic and inert nature to foods, and displacement of air that can minimize oxidation effect; major
disadvantage is its cost.
When used, liquid nitrogen usually sprayed onto food and final desirable temperature of food is -45?C which is normally attainable in 1-3 min.
For cryogenic freezing with carbon dioxide, powdered dry ice (CO2) can be mixed with the food to be frozen, or liquid carbon dioxide can be sprayed under high pressure onto the food.
Although not as cold as liquid nitrogen, carbon dioxide can offer economic advantages.

A.  Packaging for frozen foods should prevent the passage of water vapor.

B.  Due to expansion of foods with freezing (as much as 10% of volume), packages should be strong and flexible.

C.  Since foods may be stored for years, packaging should prevent transfer of light and air.

D.  Since frozen foods are commonly thawed in their package, the packaging should be liquid-tight to avoid leakage.

I.  Water loss in foods

A.  Fruits, such as dates and figs, develop high sugar contents as they dry on the tree.

B.  For thousands of years, people have dried fish and strips of meat in the air and sun to preserve them.

C.  The use of smoke and salt followed as additional preservative agents.

D.  Sun drying is still used in many parts of the world.

E.  Food dehydration = artificial drying of foods for preservation under controlled conditions (these foods often dried to ~ 1-5% final moisture).

F.  Goal is nearly complete removal of water from foods under controlled conditions that causes minimum or ideally no other changes in the properties of the food (easier said than done).

A.  Reasons for it:

1.  Preservation.

2.  Reduction of weight and bulk.

3.  Convenience

B.  Heat and mass transfer

1.  Dehydration involves getting heat in, and taking water out.

2.  Focus is usually on a maximum rate of drying, so every effort is made to speed up heat and mass transfer rates.

C.  Factors affecting heat and mass transfer

1.  Surface area (or small size is good - e.g., smaller the volume the larger the relative surface area)

a.  A larger surface area (e.g., smaller food portion) provides more surface in contact with heating medium and more surface to allow escape of water.

b.  Smaller size particle presents a shorter distance to travel for heat and moisture.

2.  Temperature

a.  Driving force = the temperature differential between the heating medium and the food (the greater it is, the greater the driving force).

b.  Also, the hotter the air surrounding the food, the more moisture it will hold before becoming saturated; therefore the more water it can carry away.

3.  Air velocity - “clothes dry more rapidly on a windy day.”

4.  Humidity

a.  The drier the air, the more water it can carry.

b.  Dryness of the air determines the final moisture content the food can be dried; each food has its own equilibrium relative humidity.

c.  At any given temperature, at equilibrium relative humidity, moisture is neither lost or gained from the atmosphere.

5.  Atmospheric pressure and vacuum - as pressure is lowered, the boiling temperature decreases.

6.  Evaporation, temperature and time.

a.  As water evaporates, it cools the surface due to the latent heat of phase change.

b.  As more moisture that is lost, the cooler the food; as food becomes drier and loses less water, the surface will heat up; this must be avoided or detrimental heating effects occur.

c.  Rule of thumb: Drying processes that employ high temperatures for short times do less damage to food than drying processes using lower temperatures for longer times.

D.  Normal drying curve

1.  Foods do not lose water at a constant rate down to complete dryness.

2.  Zero water is never reached under normal drying conditions.

3.  In a piece of drying food:

a.  Food will lose moisture from its surface.

b.  Gradually a thick dried layer develops (an insulative barrier to heat), confining moisture to the center.

c.  From the center, a moisture gradient will develop.

d.  Moisture in center has a longer path to travel than moisture near the surface.

e.  If food reaches its normal equilibrium relative humidity so that food is picking up water molecules as fast as it is losing them, and drying ceases.

4.  Drying curve will vary according to:

a.  Type of food.

b.  Kind of drier.

c.  In response to temperature, humidity, air velocity, direction of air, and thickness of food.

E.  Constituent orientation

An oil-in-water emulsion dries more quickly than a water-in-oil emulsion.

F.  Solute concentration

Solutes in solution elevate the boiling point of water, this occurs in food dehydration; thus foods high in sugars or other low-molecular weight solutes dry more slowly than foods low in these solubles.

G.  Binding of water

1.  Free water

2.  Water less loosely bound

3.  Water forming colloidal gels

4.  Chemically bound water (i.e., hydrates)

H.  Cellular structure - water is held in cells (e.g., animal, plant and microbial cells); in intact cells water is retained, in compromised cells, water leaks out.

I. Shrinkage

1.  Uniform shrinkage seldom seen in foods; water is not removed evenly and foods do not have perfect elasticity.

2.  Rate of drying will affect shape and density of food particles.

J.  Case hardening - common with foods that contain dissolved sugars and other solutes in high concentration.

1.  As water leaves cells of the food, solutes are retained by cell membranes, and air spaces in surface layers can act by capillary action whereby water carries solutes to the surface during drying and leaves them there.

2.  This causes a sticky, sugary exudate on the surface of some fruits that shrinks and clogs pores, leading to case hardening.

3.  Problem can be reduced by lowering surface temperatures and increasing drying times.

K.  Thermoplasticity (the property of softening upon heating)

1.  A cellular food (plant or animal tissue) has structure and some rigidity, fruit or vegetable juices do not and are high in sugars and such that soften and melt at drying temperatures.

2.  For example, if a sugar syrup is dried in a pan, when the water is removed, the solids will be in a thermoplastic tacky condition that stick to the pan and are difficult to remove, and with cooling, harden into a crystalline glass form.

L.  Porosity

1.  Can be developed by creating steam pressure within a product during drying; escaping steam tends to puff up the product.

2.  Porosity can also be developed by whipping or foaming a food liquid or puree prior to drying.

3.  Or by a vacuum drier by rapid escape of water vapor into the high vacuum.

4.  Advantages of porosity:

a.  quick solubility/reconstitution

b.  greater volume appearance

5.  Disadvantages of porosity:

a.  increased bulk

b.  shorter storage ability due to increase surface exposure to air, light, etc.

M.  Chemical changes

1.  Browning reactions

a.  Enzymatic browning - polyphenol oxidases (browning enzymes), polyphenols, and oxygen.

b.  Maillard browning (nonenzymatic browning) - reaction of aldehydes and amino groups of sugars and proteins, favored by high temperature.

2.  With dehydration, some loss of rehydration.

a.  Physical shrinkage.

b.  Distortion of cells and capillaries.

c.  Chemical and physical changes at the colloidal level.

(Heat and salt concentration effects can denature proteins so that the proteins cannot reabsorb water; starches and gums may be altered and less hydrophilic; damaged cells can lose water.)

3.  Loss of volatile flavor components.

A.  Method of choice depends on:

1.  Type of food to be dried,

2.  The quality level that must be achieved, and

3.  The cost that can be justified.

B.  Table 10.1: Common Drier Types.

1.  Air convection driers - insulated enclosure with means of circulating hot air and means of heating this air.

Spray driers - most important type of drier; produces more dehydrated foods than all other kinds of driers combined.
 Limited to foods that can be atomized so that the droplets are dried in seconds at air temperatures of ~ 200?C (evaporative cooling limits heating of food to ~ 80?C).
A continuous process.
Agglomeration - longer residence time in spray drier, resulting in lower moisture particles that grow in size (form clusters) in the drier; such clusters have many voids, sink in water, and are easier  to dissolve.

2.  Drum or roller driers - one of the least expensive methods of dehydration; foods usually have a more cooked character than foods dried by other methods.

3.  Vacuum driers - capable of producing highest quality dried products, but costs are higher.

Freeze drying - water will sublime if the temperature is ?0?C and pressure is ?4.7 mm; structure of food is usually quite porous.
In some freeze driers, microwaves are used to raise temperature to just under 0?C.

A.  Foods are often concentrated before they are dehydrated in a step-wise manner.

B.  Examples:

1.  Jellies and jams.

2.  Maple syrup and sugar syrups (as sweeteners).

3.  Butter.

4.  Evaporated and sweetened condensed milk.

5.  Fruit and vegetable juices, nectars, and purees (for candy-making).

6.  Tomato paste.

C.  Most food concentration aims at minimal alteration; principal reason to concentrate is to reduce weight and bulk.

Table 10.2: Commercial tomato concentrates.
Most of U.S. tomato crop is grown in Sacramento Valley and shipped east to manufacturing plants in Chicago area and east coast.

D.  Types

1.  Solar concentration for concentrating salt solutions.

2.  Flash evaporators - clean steam superheated to ~ 150?C is injected into food and boiled.

3.  Thin-film evaporators - double-jacket construction using steam, concentrated food is wiped from heat cylinder wall.

4.  Vacuum evaporators - reduced pressure for heat-sensitive foods.

5.  Freeze concentration - water forms ice crystals in chilled mixture, ice crystals removed by centrifugation through fine-mesh screen.

6.  Ultrafiltration and reverse osmosis.

a.  Use of synthetic membranes made of cellulose acetate, polyamide, etc., specific for each food and use.

b.  Pores of membranes for reverse osmosis smaller than those used for ultrafiltration.

c.  Reverse osmosis = change the normal flow of water through the membrane by applying pressure on the solute side of the membrane in excess of osmotic pressure.

d.  Liquid foods pumped under pressure through selectively permeable membranes.

For example, whey can be ultrafiltered at 40 psi first to remove proteins, and then filtered via reverse osmosis to remove water at >60 psi (Fig. 10-27).
Filters will eventually clog.

E.  Changes during concentration.

1.  Production of cooked flavors and darkening of color.

2.  Caramelization of sugar.

3.  Sandiness caused by putting a concentrated product in the refrigerator (e.g., sugar crystallization as with lactose).

4.  Protein denaturation caused by concentration of salts and minerals in solution; this will affect gel formation in foods.

5.  Microbial inactivation, although product is usually not sterile after concentration.

A.  IMFs contain 20 - 50% moisture by weight with a high portion of dissolved solutes to bind water in the product.

B.  IMFs do not require refrigeration because water is largely unavailable for microbial growth.

C.  Examples:

1.  Honey

2.  Jellies, jams & fruitcakes

3.  Figs, dates, jerky, pemmican & pepperoni

4.  Granola bars/snack bars

D.  Sorption isotherm (Figure 10.28) - relationship of moisture content to water activity (Aw).

1.  Water activity is a measure of free or available water; bound water is unavailable for microbial growth or enzymatic activity.

2.  Water activity determined relative to equilibrium moisture content or equilibrium relative humidity.

E.  Minimum growth Aw’s (pure water has Aw = 1.00)

1.  Most foodborne bacteria = 0.90

2.  Staphylococcus aureus = 0.86

3.  Most molds = 0.80

4.  Osmophilic yeasts = 0.61 (in sugar solutions)

5.  Activity of most enzymes ceases at 0.70

F.  Most packaged IMFs target an Aw = 0.85 and use antifungal agents such as potassium sorbate.

I.  GRAS bacteria commonly used to produce fermented foods; lactic acid bacteria often compete with yeasts in high sugar environments.

II.  Their names

A.  Lactococcus - all are homofermentative.
B.  Lactobacillus - some homofermentative, some    heterofermentative.
C.  Leuconostoc - all heterofermentative.
D.  Pediococcus - all homofermentative.
E.  Also included: the thermophilic dairy strep - Streptococcus  thermophilus and some members of the enterococci,    homofermentative.

Mainstream food fermentations

I.  Primary cultures used

Yeast: species of Saccharomyces
Lactic acid bacteria:  Lactobacillus, Lactococcus, Pediococcus and Leuconostoc

For yeast:  Produce ethanol and carbon dioxide in manufacture of alcoholic beverages and leavened products (breads).
For lactic acid bacteria:  Produce lactic acid and other organic acids  in acidulated products (cheese/yogurt, fermented sausages, fermented produce - pickles, sauerkraut, olives).

Fermentable sugars (monosaccharides and disaccharides) present.
Exclude undesirable microorganisms by using salt, anaerobic conditions, temperature control.

__________

Videotape on cheese-making

__________

I.  Originally from goat's milk or sheep's milk/ in U.S.A. it's whole or skim cow's milk

II.  Many variations of yogurt (yoghurt/yohourth/yaourt), for example:

A.  doogh: spiced, watered, carbonated yogurt (Iran)
B.  kishk: blend of wheat flour and yogurt (Lebanon)
C.  kashk: yogurt cheese, flavored with herbs, drained and dried in bags

A.  Milk adjusted to 10.5 to 11.5% solids
B.  Heated to 90?C/30 to 60'
C.  Cooled to 40 to 45?C/3 to 5 h
D.  Inoculated with Streptococcus thermophilus and Lactobacillus   bulgaricus at 1:1 (should maintain this ratio, otherwise a new starter is  needed)
E.  Fermentation stopped by cooling to 5 to 10?C/final pH 3.65 to 4.40  (final population of two cultures is about 1 x 109 CFU/g - then   declines).

I.  Both are needed for adequate production of acetaldehyde, acetic acid, and diacetyl (most of the acetaldehyde produced by L. bulgaricus).

II.  The coccus grows faster than the rod and is primarily responsible for acid production; S. thermophilus takes pH to 5.0 and prevents excessive acetaldehyde production by L. bulgaricus.

III.  But S. thermophilus is stimulated by L. bulgaricus, most likely by critical metabolites, such as free amino acids.

IV.  The rod adds mainly flavor and aroma, but takes the pH down to 4.0 to 4.4 (it is more active in latter stages of fermentation).

V.  L. bulgaricus is stimulated by S. thermophilus by the initiation of lactic acid production and reductionm of oxygen levels in milk.

Probiotics

I.  Yoghurt a preferred product for inclusion of probiotic cultures.

The intent is to seed or elevate levels of these desirable bacteria in the GI tract.

Bifidobacterium - several species are used.
Lactobacillus acidophilus - as well as Lactobacillus casei.

Stabilization of intestinal microbiota/Resistance to enteric pathogens (e.g., diarrheal diseases).
Reduction of toxic metabolites and detrimental enzymes.
Improvement of lactose tolerance to consumption of milk products.
Reduction of serum cholesterol.
Promotion of cell-mediated immunity.
Production of nutrients and vitamins/Aid in calcium absorption.
Intestinal recolonization following antibiotic treatment, chemotherapy or radiation treatment.

_________

Video clip on probiotics in dairy products

_________

Packaging 305  --  Moved back in semester.  Guest speaker: R.W. Keown, 4/18/01.

_____________________

Brewing Beer

I.  Comparison to leavened bread
 

A.  Same type of yeast is used, Saccharomyces cerevisiae, although specialized variants are now employed (i.e. bakers' yeast vs. brewers' yeast).

B.  In bakers' yeast, the production of carbon dioxide is all important (for  leavening), but for brewing, carbon dioxide production is secondary to ethanol production.

[In bread, the alcohol is lost or volatilized by the heat of baking]

C.  Original substrate for both fermentations is derived from grain, although baking is a solid-state fermentation and brewing is a fermentation in liquid.

A.  Malt - a package of enzymes and food substances for the yeast.  The malting process is necessary to activate enzymes in the plant material:

1.  Barley grains soaked in water/germinated, then dried

2.  Most sprouts are removed and the malt remains

3.  Malt crushed before use (the malt is the source of amylases and proteinases)

B.  Mashing - done to make soluble the valuable portions of malt and malt adjuncts to cause breakdown of starch and proteins.  In the mashing process:

1.  Ground malt mixed with water and warmed

2.  Cooked starchy malt adjuncts added and temperature raised to 65 to 70?C

3.  At 65 to 70?C, saccharification occurs

4.  Temperature raised further to inactivate enzymes

5.  Insoluble materials settle to bottom, the filtered liquid is called wort

C.  The wort is boiled with hops for about 2.5 hr and cooled

1.  After boiling, the wort is then sterile,

2.  Flavor compounds extracted from the hops,

3.  Additional insoluble components of wort precipitate out upon cooling

[Then the actual fermentation is started]

D.  The wort is pitched with yeast

E.  Fermentation proceeds at a controlled temperature (primary fermentation)

F.  "Green beer" is filtered and lagered (stored at a lower temperature, may be referred to as a secondary fermentation)

G.  After lagering,

1.  beer is filtered/clarified to remove last remnants of yeast and other particulates,

2.  pasteurized,

3.  charged with carbon dioxide,

4.  packaged and shipped.

I.  Primary cultures used

Yeast: species of Saccharomyces
Lactic acid bacteria:  Lactobacillus, Lactococcus, Pediococcus and Leuconostoc

II.  Products:

For yeast:  Produce ethanol and carbon dioxide in manufacture of alcoholic beverages and leavened products (breads).
For lactic acid bacteria:  Produce lactic acid and other organic acids  in acidulated products (cheese/yogurt, fermented sausages, fermented produce - pickles, sauerkraut, olives).

III.  General methods

Fermentable sugars (monosaccharides and disaccharides) present.
Exclude undesirable microorganisms by using salt, anaerobic conditions, temperature control.

_________

Soy sauce fermentation vs. chemical method

Chemical methods is cheap, quick and results in an inferior product; relies on acid hydrolysis (8-10 h) of the soy meal using concentrated HCl followed by neutralization with sodium carbonate and filtration.

Fermention uses 3 days of growth of Aspergillus on roasted soy meal and crushed roasted wheat followed by brining and 6 mo-1 yr fermentation with lactobacilli and yeasts, then filtration/pasteurization and packaging.

__________

Foods derived from rDNA technology, PowerPoint presentation - 4/4/01.

Food Packaging - R.W. Keown, 4/18/01

__________

I.  Fat consumption and nutritive value

A.  Much attention is directed towards the long-term effects of fat in the diet.

B.  Fat is a concentrated energy source.

C.  Much of the opinion is that fat is bad.

Estimated that ~40% of calories in American diet supplied by fat; recommendation that this level be lowered to ~30%.

D.  Some fats are good fats, e.g., essential fatty acids such as linoleic acid, and ?-3 PUFAs (polyunsaturated fatty acids).

E.  Also, fats ‘carry’ the fat-soluble vitamins (A, D, & E).

F.  In foods, the major types of fats that are encountered are the triglycerides, fatty acids, phospholipids, and sterols; triglycerides predominate.

A.  Solubility - essentially, this function determines if a compound is a fat; if a compound is water-insoluble, it is a fat (within reason).

Fats are soluble in such organic solvents as chloroform, hexane, and ether.

B.  Melting point:  By convention, if a lipid is solid at room temperature, it’s a fat; if a lipid is liquid at room temperature, it’s an oil.

1.  For triglycerides the types of fatty acids esterified to the glycerol backbone largely determines the properties of the triglyceride.

Fats high in saturated fatty acids, are normally solid at room temperature.
Fats high in unsaturated fatty acids, are normally liquid at room temperature.
The length of the fatty acids also affects melting point; long fatty acids increase the melting point of a fat.
All food fats are mixtures of triglycerides containing different levels and types of fatty acids, therefore fats usually do not have a sharp melting point.

2.  Hydrogenation

a.  Developed to change liquid vegetable oils into solid plastic shortenings and margarines.

Shortenings = “the first cousins of margarine”, they are made from the same types of oils used in making margarines, but do not contain water.
A shortening that remains plastic over a wide range of temperature is suited to most bakery operations.

b.  Hydrogenation also stabilizes oils to prevent spoilage from oxidation (fat rancidity).
 Unsaturated fatty acids are highly reactive with oxygen at their double bonds.

c.  Process

In a heated reactor, hydrogen gas is bubbled through the oil (usually soybean oil, also known as vegetable oil) in the presence of a nickel catalyst.
As a result, some unsaturated double bonds are converted into saturated bonds and melting point is increased.
Different degrees of hydrogenation can be obtained; blends of fats are often done depending on the use of the fat.

d.  Health implications - in addition to reduced levels of polyunsaturated fatty acids.

Hydrogenation converts some cis double bonds of polyunsaturated fatty acids to trans double bonds.
Trans double bonds do not occur frequently in nature; in U.S. most trans fatty acids come from hydrogenated vegetable oils.
Trans fatty acids are not metabolized in the body as are cis fatty acids; mechanism is unclear but it appears trans fatty acids may elevate serum cholesterol levels.

C.  Plasticity - the ability to be molded or shaped; in plastic fats, both solid crystals and liquid oil are present.

Plastic fats used in baked goods and pastries; plastic fats can be creamed (mixed with the incorporation of air).
Plasticity influenced by the state of fat crystallization.
Fats can be made more plastic by chilling and agitation which affects crystallization rate and form; heat exchangers are used to do this.

D.  Flavor contributions - different food fats have different flavors and aromas.

A.  Plant lipids

1.  Vegetable oils =  soybean (>60% of vegetable oils used),

cottonseed (America’s first vegetable oil; by-product of cotton industry),
sunflower (good stability),
peanut (excellent oxidative stability),
olive (most expensive edible oil; virgin refers to olive oil from the first     pressing),
corn (used principally in margarines),
canola (from rapeseed), and
safflower (highest content of PUFAs) oils.

2.  Also used: coconut (high in saturated fat), palm (from fruit rather than kernel of palm tree; currently only behind soybean oil as world’s most popular edible oil), and palm-kernel oils.

3.  Selection of oil usually based on cost, oxidative stability, and flavor.

B.  Animal lipids

1.  Lard - probably the oldest culinary fat; it is rendered hog fat.

a.  Rendering = after butchering, fatty tissues are heated, and the melted fat separates from the connective tissue and other residues; lard generally lacks uniformity.

b.  Best lard comes from leaf fat that lines the abdominal cavity.

c.  Health implications has severely curtailed its use, although still the preferred fat in Mexican cuisine.

d.  Lard does possess excellent shortening power (ability of a fat to cover a large surface area to minimize the contact between water and gluten during the mixing of batters and doughs resulting in a softer, more tender texture).

2.  Butter = the fat of cream that is separated from other milk constituents by agitation (churning).

b.  Process = the protein/lecithin film that normally surrounds the fat globule of cream is mechanically disrupted, thus breaking the ‘oil-in-water’ emulsion and allowing the fat  globules to coalesce.

c.  Butter is actually a ‘water-in-oil’ emulsion (18% water & 80% fat); a small amount of protein acts as the emulsifer.

d.  Buttermilk remains after butter is churned from cream.

e.  Lactic acid bacteria may be added to pasteurized sweet cream for better flavor and keeping quality (sweet butter does not have sugar added; it means the butter has been made from  ‘sweet’/unsoured cream).

f.  Depending on the color of the cream, an extract of annatto seed or carotene may be added.

g.  Salt (~2.5%) is usually added for flavor and to serve as a preservative.

All types of food fat undergo some kind of processing.

A.  Pressing or expelling

1.  To squeeze oil from oilseeds.

2.  Oilseeds usually cooked slightly to breakdown the cell structure to enhance the release of oil (but heat should not be so high as to darken the oil).

3.  Seeds may be ground or cracked for the same purpose.

4.  For some seeds such as corn, only the germ is pressed to obtain the oil.

5.  Crude oil usually clarified by filtering or by centrifugation.

B.  Solvent extraction

1.  Common procedure to remove oil from cracked seeds at low temperatures with a nontoxic fat solvent such as hexane.

2.  Hexane percolated through seeds, after oil extracted, hexane is distilled from the oil and recovered for reuse.

3.  Oil yield greater with extraction than pressing; sometimes the two processes are combined.

4.  Oil-free residual seed meal is ground for animal feed.

C.  Degumming

1.  Phospholipids and protein-fat complexes are gummy.

2.  These compounds found in vegetable oils derived from pressing or solvent extraction.

3.  When wetted with water, these compounds become oil-insoluble and settle out.

4.  This is how lecithin can be obtained.

D.  Refining - treatment with alkali.

1.  To settle additional minor impurities from oil missed by degumming.

2.  Free fatty acids combine with alkali to form soaps.

3.  Soaps removed by filtration or centrifugation.

E.  Bleaching - passing heated oil over charcoal or adsorbent clays and earths.

1.  To remove plant pigments such as chlorophyll and carotene.

2.  Animals fats can usually be bleached by heat alone.

F.  Deodorization

1.  Natural fats & oils can contain low-molecular weight odorous compounds.

2.  Desirable in some fats (e.g., olive oil, cocoa butter, lard, fresh butterfat, chicken fat); however, fish oils and some seed oils have undesirable odors.

3.  Removed by heat and vacuum, or adsorption onto activated charcoal.

G. Winterizing

1.  When oil is chilled, triglycerides with high levels of saturated fatty acids and with longer length fatty acids will tend to crystallize out of the oil.

2. Therefore, before the final product is bottled, it is cooled and crystals are removed.

H.  Monoglyceride (glycerol ester containing one fatty acid) and diglyceride (glycerol ester containing two fatty acids) preparation.

1.  Heat oil to ~200?C with glycerol and NaOH added.

2.  This is done under an inert gas or with vacuum to prevent oxidation.

3.  Glycerol esters are partially charged and serve as excellent emulsifiers.

A.  First developed in 1869 by a French chemist, Mege-Mouries, in response to the offer of a prize from Napoleon III for an alternative for butter (Mege-Mouries used beef fat as the primary ingredient).

B.  Margarine use has increased while butter use has decreased.

Margarines are cheaper.
Margarines contain no cholesterol.
Margarines have improved in quality, uniformity and product types while becoming the ‘mainstream’ table fat.

C.  FDA standard of identity - water-in-fat emulsion containing at least 80% fat.

D.  Soybean and cottonseed oils extensively used in margarines.

Also contain emulsifiers, salt, butter flavor (diacetyl), color and preservatives (e.g., sodium benzoate) as well as vitamins A & D.
Water-soluble ingredients mixed in water, fat-soluble ingredients mixed in oil, and then these two phases mixed at refrigeration temperatures.

E.  Margarines high in PUFAs are usually soft (packaged in tubs) because they contain more oil that has not been hydrogenated.

F.  Reduced-calorie margarines do not meet margarine standard of identify; must be called vegetable oil spread or corn oil spread, etc.

G.  Reduced-calorie margarines:

Contain less fat; contain more water (and thus require a stronger emulsification system); calories reduced by 33% or more.
Contain more air (are whipped); volumes increased by 50%.

A.  For frying, shortenings with short plastic ranges and low melting points preferred; these properties minimize greasiness from unmelted fat in the mouth when fried foods eaten.

1.  Oils are neutral in flavor, have a high enough smoke point to make them useful in frying, and have good shortening power.

 Smoke point = the temp. at which smoke comes continuously from the surface of a heated fat/oil.

2.  Shortenings used in baking have monoglycerides and diglycerides (emulsifiers) added to allow higher proportions of sugar and liquid to be added to the fat (e.g., cake formulas), but addition of emulsifiers lowers the smoke point of the fat, so emulsifiers not as desirable in fat used for frying purposes.

A.  Hydrolytic rancidity = triglycerides breakdown and fatty acids are released.

Lipases (enzymes) cause this; short-chain fatty acids produce very disagreeable odors and flavors (e.g. caproic acid = essential of old goat).
Heat

B.  Oxidative rancidity = triglycerides breakdown when unsaturated fatty acids exposed to oxygen, resulting in highly reactive derivatives that produce unpleasant rancid odors and flavors.

Oxidative rancidity most responsible for spoilage of fats and fatty foods.
Vitamins A and E lost in this reaction.

C.  Controlling storage conditions.

1.  Exclude light, moisture, and air (oxygen).

2.  Keep refrigerated.

3.  The industry adds antioxidants to prevent rancidity;
examples include: vitamin C, ?-carotene and tocopherols (vitamin E), BHA (butylated hydroxyanisole), and BHT (butylated hydroxytoluene).

4.  And avoid reusing old cooking fat.

Hydrogenated vegetable oils
Margarines contain no cholesterol (when 100% vegetable oils are used) and have less saturated fat than butter
Margarines often contain:

1.  artificial flavors and colors

2.  sodium benzoate as a preservative

3.  vitamin A (to match the concentration found in butter)

Diet margarines and spreads:

1.  Compared to regular margarine, have more water and less fat (less calories)

2.  More air (mechanical whipping to form a fat foam)

Mayonnaise:

1.  Federal law requires commercial mayonnaise to contain at least 65% oil; most contain 80%.

2.  Flavor dependent upon vinegar and seasonings used.

3.  Imitation mayonnaise contains more water than oil (fat range is from 19 to 48%), and vegetable gum to increase viscosity.

1.  Starch, egg and water are cooked together to form a "pudding-like" mixture; legally required to have 30% oil.

2.  Nonfat dressings commonly use the following ingredients:

a.  water

b.  corn syrup (glucose)

c.  modified starch

d.  dried corn syrup

e.  salt and sugar

f.  cellulose gel/vegetable gums

g.  vinegar (lowers pH; a preservative agent)

I.  Fat replacements

A.  Created by taking normal food ingredients, such as proteins from eggs and milk, water, or various carbohydrates, and processing and combining them to produce an ingredient that has some of the properties of fats without their calories or artery-clogging characteristics.

1.  Polydextrose

a.  Starch-based fat replacement

b.  Currently used in frozen desserts, puddings, and cake frostings

2.  Maltodextrin

a. Starch-based fat replacement

b.  Used in salad dressings and margarines

A.  Differ from fat replacements; usually have even fewer calories

B.  Substitutes are a single, unique ingredient to replace fats

C.  Simplesse?

1.  Used in the manufacture of ice cream, salad dressings, and cheese products

2.  Has a fat-like consistency and texture because it is composed of proteins from either milk or egg whites that have been heated and blended to create nearly microscopic spheres of protein

3.  These particles mimic mouthfeel of real fat globules; they’re creamy, smooth texture

4.  A drawback is that Simplesse? does not retain its fat-like consistency and taste when heated

D.  Olestra?

1.  Can withstand heat

2.  It is a sucrose polyester; that is, a sucrose molecule to which six, seven or even eight fatty acids are attached

3.  Olestra? comes closer to mimicking the structure of triglycerides than Simplesse?

4.  Fat-digesting enzymes do not break down Olestra?; it by-passes the body’s digestive and absorptive mechanisms because Olestra? is much larger than a triglyceride

5.  Concern: “Fake fat - Miracle or Menace?”

a.  Guilt-free snacks sound great, but some physicians warn they’re unfit to eat

b.  Loss of fat-soluble nutrients

1.) Vitamins A, D, E and K (Proctor & Gamble will fortify Olestra with these)

2.) Carotenoids (fat-soluble; P&G will not fortify Olestra with these)

6.  Proctor & Gamble

a.  Over 25 years of research with Olestra including more than 100 studies in animals and 98 human studies with more than 4,300 men, women and children

b.  Statement: Does not affect carotenoid concentrations any more than other common foods (6 to 10% drop).

7.  FDA approval of Olestra

a.  A warning label

1.) Product contains Olestra

2.) May cause abdominal cramping and loose stools

3.) Olestra inhibits the absorption of some vitamins and other nutrients

4.) Supplementation with A, D, E and K

b.  Surveillance and monitoring of Olestra consumption and complaints will continue

c.  Olestra approval restricted to snack chips and crackers, such as potato chips, tortilla chips, cheese puffs and club crackers

8.  Calorie/fat issues

a.  Example: A 1-ounce serving of regular potato chips contains 150 calories and 10 grams of fat; a comparable serving of potato chips made with Olestra has 70 calories and no fat.

b.  Upcoming Olestra-containing foods

1.) French fries

2.) home-cooking oils

3.) pastries

9.  Olestra is unlikely to lower the prevalence of obesity or to improve the nutritional habits of Americans.

Dietary Supplements

4/18/00

A.  Cereals are plants that yield edible grains; these include wheat, rice, corn and rye.

1.  The grains provide the earth’s human population with most of its calories and about half of its protein.

2.  In world, rice is most important food (~560 million metric tons/yr); wheat is a close second and closing (~530 million metric tons/yr).

Nearly all rice goes directly to humans; >90% grown in Asia where most of it is consumed; rice flour is not a strong flour.
Most wheat goes directly to human, only a small portion goes to animals; wheat production in U.S. is ~66 million metric tons/yr.
Most corn goes to animals; much of the world’s corn grown in the U.S. (globally ~470 million metric tons/yr; in U.S. ~200 million metric tons/yr).

3.  Protein derived from cereals is often nutritionally deficient (lack certain essential amino acids).

Dates of domestication: Wheat 7000 BC; Rice 4500 BC; Maize 4500 BC.

Soybean is a legume, but is also considered an oilseed due to its high fat content.

Cereal proteins not as nutritionally complete as most animal proteins, notable deficiencies in lysine, methionine/cysteine, threonine and tryptophan.
Anatomy of a wheat kernel: endosperm, fruit and seed coats (bran), embryo (germ).

1. Classified as hard (high in protein; forms a more elastic dough for bread-making) and soft (relatively low in protein; yields weaker flour better for cake-making).

2.  For human consumption, wheat is usually first converted to flour.

a.  Conventional milling: the format is basically a progressive series of disintegrations followed by sievings.

Upon receipt, wheat is cleaned of foreign seeds and soil; water is added to reach ~17% moisture; wheat kernels run through rollers set progressively closer and closer together.
First rollers break open the bran and free the germ from the endosperm; rolling continues to pulverize the brittle endosperm and flatten the germ; flakes of bran and germ removed through sieves; pulverized endosperm further ground into flour. (Rollers usually grooved with one rotating faster than the other in order to separate germ and bran from the endosperm.)
The functionality of a flour primarily based on its carbohydrate to protein ratio.

b. Finer fractions of flour have lower amounts of contaminating germ and bran; thus these fractions are whiter in color and better in bread-making quality, but lower in vitamin and mineral content.

c.  The protein-to-starch ratio is dependent upon the variety and kind of wheat from which it was ground.

3. Turbomilling

a. Flour from conventional milling further processed to separate flour into higher protein or higher starch fractions by using special high-speed turbo grinders.

b. Endosperm agglomerates (chunks of starch and gluten together) are further broken apart and their densities differ enough to be separated by a stream of turbulent air.

Finer protein particles rise/starch particles settle.
An air classifier separates fractions using centrifugal force on suspended particles.

c. Turbomilling enables separation of flour into fractions that can be blended in any desired ratio allowing the formulation of custom-blend flours for bread-making, cookie-making, etc.
In the endosperm, each cell is tightly packed with starch granules.

4. Uses of wheat flour and granules - breads, sweet doughs, cakes, biscuits, doughnuts, crackers, breakfast cereals, gravies, soups, confections and alimentary pastes (noodles and pasta products).
Alimentary pastes - mostly milled wheat and water in 100:30 ratio; usually hard durum wheat is used which is milled to coarse particles know as semolina, further milling produces fine durham flour; eggs, salt and other minor ingredients may be added; product is not leavened; often extruded and oven-dried to 12% moisture.

1. Consumed as the intact grain minus hull, bran and germ.

2. Therefore milling process designed not to disintegrate the endosperm core of the seed.

3. Milling - To shellers or hullers that are abrasive disks or moving rubber belts; jets of air separate hulls from kernels; inner layers of bran and germ dislodged by rubbing action of a ribbed rotor; the higher the degree of milling or polishing, the lower the remaining vitamin and mineral contents.

4. Constant search for more improved varieties; however, in Asia, wheat is becoming more popular, thus lessening this need.

Figure 17.7. Flow diagram of the wet-milling process, page 393 of textbook.

1. In harvested wet form, consumed as a vegetable.

2. Popcorn variety is dried, moisture in center explodes kernel when heated (the original puffed cereal).

3. Dry milling - corn conditioned to ~21% moisture and passed between rotating cones that loosen the hulls and germ from the endosperm; then dried to ~15% moisture to facilitate roller milling and sieving, hulls removed by jets of air; brittle endosperm flattened and endosperm recovered as coarse grits or corn meals or with further rolling, corn flour.

4. Wet milling (Fig. 17.7, pg. 393 in text) - kernels steeped in warm water containing acid and sulfur dioxide (as a preservative); kernels passed through a mill to become a pasty mass that is pumped to water-filled settling troughs where lighter germ floats to top and slurry passed through screens that remove the hulls; remaining slurry passed through centrifuges to separate heavier starch from lighter protein; fractions dried, starch fraction to corn starch, protein fraction to yield corn gluten (zein) commonly used in animal feeds; corn starch used to make corn syrups.

5.  High fructose corn syrup (HFCS) - currently in U.S., the primary ingredient sweetner.

a. Development of HFCS manufacture a direct result of the political situation of Castro’s revolution in Cuba leading to the loss of the main American source of table sugar (Cuban sugar cane).

b.  The process starts with corn starch (polysaccharide made of glucose), corn starch solution treated with the enzyme, ?-amylase, the amylase removes individual glucose units from the starch (but glucose is not very sweet), the glucose solution is then treated with the enzyme, glucose isomerase (converting glucose to fructose), and fructose is sweeter than sucrose and far more sweet than glucose.

1.  A curiosity in the U.S. until 1900, is now the single largest cash crop bringing more protein and more oil into the economy than any other single source.

2.  A native of northern China (domesticated in ~1000 B.C.), soybeans were spread in part by the vegetarian doctrine of Buddhism.

3.  Soybeans were introduced to the U.S. upon the return of Commodore Matthew Perry’s expedition to the Far East in 1854; today the U.S. produces ~75% of the world’s crop.

4.  Initial commercial interest was focused on the bean’s high oil content (18% oil by weight); the oil was used in soaps, paints and varnishes.

5.  Due to its high degree of unsaturation, there were stability problems (subject to oxidation and off-flavors), but with the discovery of hydrogenation, soy margarine replaced butter for most people in WWII.

6.  Soybean protein has the highest quality of proteins from legumes, but only in the Far East are soybeans a significant human food; the bland flavor of soybeans has encouraged the development of highly flavored fermented products such as soy sauce; tofu (bean curd) is another form of processed soybeans.

7.  A food-grade flour of ~50% protein is available, along with partially defatted flours.

8.  These flours can be further concentrated in protein to make soy protein isolates.

Soy Sauce

I.  By fermentation: Start with roasted soy meal and crushed roasted wheat, moisten and ‘ferment’ 3 days with the mold Aspergillus (this is not the aflatoxigenic varieties of Aspergillus, A. flavus and A. parasiticus); after starch and protein molecules are broken down by mold growth, the meal is brined and lactobacilli and yeast ferment the mixture for 6 months to a year producing ethanol and acids and other by-products; the liquid is then filtered and pasteurized, the solid cake going to cattle feed.

II. The quickie chemical method: Using roasted soy meal, a liquid mixture is hydrolyzed with hydrochloric acid for 8-10 h, this mixture is neutralized with sodium carbonate (to pH 4.7), filtered and bottled.  This product has fewer flavor constituents and is generally regarded as inferior to the fermented soy product.

Tofu/Bean Curd

I.  The Method: Soak the whole soybeans overnight to allow removal of the outer hulls, mash the beans and pressure cook, filter to obtain a solution (soy milk) to which calcium sulfate and calcium chloride are added to precipitate proteins; the curds settle and are drained, then pressed into cakes, washed and packaged = bean curd.

II.  Similar to soft cheese, tofu is very bland, but picks up the flavors of foods it is associated with; can be used to extend animal protein foods; thus adaptable for egg dishes, casseroles, breads, and vegetable and meat dishes.

 III. Textured vegetable protein (TVP) = ragged, porous granules of isolated soy protein tha rehydrate quickly (a ‘more modern’ form of tofu for use by the food industry); used to extend meat it is available commercially with or without flavor; best used with highly flavored dishes such as curries, tomato sauce, taco fillings, hamburger stroganoff, lasagna, chili, etc.; TVP is fat-free but will absorb fats/oils very readily.

IV.  Meat analogs = imitation meat products derived from soy protein into numerous forms resembling meats, such as sausage, bacon, ham slices, chicken and beef chunks; often fortified with vitamins and minerals and methionine; useful for vegetarians, less fat (or none at all - any fat present is less saturated), no cholesterol, but usually quite high in sodium content and cost is more than the meat original.

V.  Figure 17.13, pg. 405 class textbook: Emphasis on different fractions of soybean and basics of their production - protein concentrate (70% protein), simple isolate (90-95% protein), TVP (50-55% protein); use of aqueous extractions using acid, alkali and alcohol; soy protein slurry extruded into acid bath for formation of fibers for compaction into meat tissue-like sections.

Peanuts

1.  Both a legume and an oilseed with ~25% protein and ~50% oil.

2.  Peanut flours, protein concentrates and protein isolates produced, but limited in application to human foods.

3.  Protein of peanut not as high in lysine as that of soybean.

4.  Principal uses are as whole nut, source of peanut oil (with peanut meal going to livestock), and in U.S., as ground nuts in the form of peanut butter.

5.  About 2/3 of world’s peanuts pressed for oil and supply ~1/5 of all edible oil production.

6.  Over half of U.S. crop goes to peanut butter, that is made by

• shelling the nuts,
• roasting,
• removing the skins and hearts with heat followed by rubbing,
• grinding,
• adding salt and sugar for flavor,
• emulsifiers to keep the oil suspended, &
• packaging.

SCP - Spirulina

I.  Single-cell protein: The growth of microorganisms as a food source with primary interest on protein production; types of yeasts have been used for this purpose, i.e. Saccharomyces cerevisiae.

II.  Spirulina is the genus name of a type of blue-green algae that has been used for centuries as human food; now found in many health foods.

A. Grows abundantly in natural alkaline tropical lakes where malnutrition is often endemic; first discovered by Western civilization in Mexico with invasion of Cortez; Aztecs harvested Spirulina from lake surface and dried/ground it for use as a flour in biscuits, soups, etc.; Spirulina also used in East Africa as food source.

B. Very alkaline pH ensures that carbon dioxide is retained in water, thus decreases growth of other microorganisms including pathogens.

C. Spirulina floats, which makes it easy to harvest.

D. One of the richest sources of protein of nonanimal origin; cells of Spirulina contain vitamins and growth factors important in human nutrition, such as ?-linolenic acid and vitamin B12.

E. Nucleic acid concentration of Spirulina is the lowest for microbial cells used as SCP.

F. The cell envelope of Spirulina is more easily digestible than that of yeast or other unicellular algae.

G. The yields per unit area are exceptional in controlled systems: 12.5 acres for meat from cattle on grassland to supply for year protein requirement for one person, 2.5 acres for wheat, and 10 square yards for Spirulina.

H.  Growth requirements minimal: Photosynthetic and water.

I. Nutritional and toxicological tests show Spirulina safe, recorded history shows everyday consumption has no harmful side effects.

[P.S. Psyllium is a plant source of fiber comprises of such compounds as lignin and cellulose.]

1.  Special strains of chickens are bred for large-scale egg production.

2.  An average layer lays >260 eggs/yr.

3.  ~70 billion eggs are produced in the U.S. each year.

4.  ~90% are consumed directly as shell eggs; the remainder broken out of the shell and processed, most going to bakery, confectionery and noodle industries as well as for some nonfood uses.

The Libido Story (Prepared Foods, April 1996, pg. 39)

1. In Norway, Dr. Bjorne Eskeland and colleagues isolated a substance from fertilized hen eggs.

2. Using double-blind studies, consumption of this egg product heightened sexual arousal in >80% of men tested and boosted testosterone levels in some by as much as 35%.

3. It may also foster endurance and muscle development in athletes.

4. Data evaluated at Toronto's Mt. Sinai Hospital; appears real.

5. Initial rights purchased by Miami-based Value Holdings Ltd.

6. The food ingredient is under review by both the FDA and USDA.

7. Now under development, this high-performance egg ingredient has been dubbed "LIBIDO"; a Delaware-based company, Virilité Nutriceuticals Corp. was created to commercialize the technology.

8. First product: An energy bar, is expected to be brought to market within the next 60 days; the 30-gram bar will offer 2 grams of Libido per serving.

9. Second product: An isotonic beverage offering 1 gram of Libido per serving and a host of other nutrients.

10. Other works in progress: Granola and yogurt bars, juice beverages, and beer.

11. Upcoming: A 3-year, 1,000-subject clinical trial under  review by the Canadian Health Protection Branch in Ottawa.  This will include examination of potential benefits for women.

I.  For domestication, the egg of the chicken.

A.  Biology of the egg versus the egg as food.

B.  As a food ingredient, eggs serve several different functions.

Used to make emulsions (yolk contains lecithin).
Contains foaming agents (whites of eggs)
Proteins of egg coagulate upon heating (e.g., baked custards).
Egg yolk provides color; egg white provid