Transcript Slide 1

Unit
Food Science
Problem Area
Handling and Storing Plant
Products
Lesson
Testing for Food Additives
Student Learning Objectives
1. Describe food preservation and its
benefits.
2. Describe the methods used in
controlling food contamination.
3. Explain why food additives are
important to food preservation.
4. Explain a variety of food additives and
their purposes.
Terms
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air-blast freezing
antioxidants
blanching
chemical drying
commercial sterilization
conduction
convection
drying
fermentation
flavor enhancer
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food additives
food preservation
food spoilage
freeze drying
freezing
irradiation
liquid freezing
mechanical drying
pasteurization
pickling
Terms cont.
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plate freezing
radiation
refrigeration
senescence
sequestrants
sterilization
texture enhancer
What is food preservation? How does food preservation
benefit consumers?
 All foods eventually undergo spoilage; some spoil much
faster than others. Foods can undergo natural
deterioration or can become contaminated by
microorganisms causing spoilage to occur at a much
faster rate.
 Senescence is considered to be a terminal, irreversible
deteriorative change in living organisms, leading to
cellular and tissue breakdown and eventually death.
Senescence is the period following ripening, during
which growth ceases and aging processes replace
ripening processes.
 A. Food preservation is the treatment of food to keep it
from spoiling. It also aids in retaining nutrients and
improving taste.
 B. Food spoilage is the condition in which food
becomes unsafe to eat. Food spoilage can be caused by
the invasion of bacteria, fungi, mold, and other foreign
materials.
 1. Bacteria are one-celled microscopic plants. They are the
most difficult of all microbes to control in the prevention of
food spoilage. Microorganisms use the food as a food
source.
 2. Food may be exposed to other foreign materials. These
materials are not intended to be part of the food. Their
introduction leads to spoilage. Examples of foreign
materials that cause food spoilage are rodents, insects,
and chemicals.
 C. Food preservation helps foods retain their nutritional
value. As foods deteriorate, they lose the nutrients that
they naturally contain. Fruit juices that are not
refrigerated typically lose their nutrients. The loss of
nutrients is known as nutrient depletion.
 D. Food preservation aids in helping foods retain their
taste. Palatability means that an item has an agreeable
taste. Various processes are used to improve food
palatability. Care must be taken to not decrease a food’s
nutritional value when increasing its palatability. For
example, sugar is added to foods to improve its
palatability. How-ever, if too much sugar is added, the
nutritional value of the food is decreased.
What are the methods used in food science to control
contamination?
 Environmental controls that are commonly used
in storage of perishable plant products are:
 A. Heat—Most bacteria, molds, and yeasts grow
best at temperatures of 16–38ºC. For sterility, a
temperature of 121º C must be maintained for at
least 15 minutes. Heat is the most effective
means of preserving a food product. It is
commonly used in canning foods.
1. In food processing, heat energy is transferred in one
of three ways to aid in preservation:
a. Conduction is a method of heating in which
energy moves from one particle to another through
direct contact. Conduction may be compared to a
chain reaction. As each particle of food is heated, it
passes energy on to other particles it is touching.
Examples of foods that are preserved through
conduction heating include canned tuna or ham.
b. Convection is a method of heating that involves
the movement of a heated air or liquid through the
food being heated. This is the same type of heat
used in a kitchen oven. In convection heating, the
movement of the heated air or fluid around the food
causes it to be heated. Examples of foods that are
preserved through convection heating are canned
soups.
c. Radiation is a form of conduction in which
heat energy is transferred through the
electromagnetic spectrum. The electromagnetic
spectrum is a linear arrangement of all known
forms of energy. In radiation, energy from the
infrared and ultraviolet range of the spectrum are
used to heat the food. An example is the infrared
radiation lamps used in restaurant buffets to
keep food warm.
2. Heat preservation is the most complete means of
food preservation. When food is heated, it is altered.
The extent to which a food is altered depends on the
amount and duration of heat it is subjected to.
a. Sterilization is the complete destruction of all
microorganisms. Sterilized foods will last a very long
time. Because they have undergone a high level of
heat treatment, sterilized foods go through significant
alterations.
b. Commercial sterilization is the complete
destruction of all microorganisms except some
spores. Commercially sterilized foods will eventually
become unsuitable to eat. They will not cause
sickness. Instead, they become unpalatable.
c. Pasteurization is a heat treatment that
destroys all pathogenic microorganisms, but not
organisms that cause spoilage. A pathogenic
organism inflicts illness in humans.
d. Blanching is a heat treatment used with
vegetables where their temperature is raised to
between 180° and 190° and followed by rapid
cooling. This process does not destroy
microorganisms. It does inactivate enzymes that
might alter the taste or color of the vegetable.
 B. Cold—When water in foods is completely frozen,
there is not multiplication of microorganisms. At a
temperature of below 10º C, growth is slowed and
becomes even slower as the cold increases. Cooler
temperatures slow senescence. Refrigeration and
freezing are not as effective as heating in preserving
foods. Heating destroys all microorganisms. Cold
treatments only slow the metabolisms of the
microorganisms.
1. Refrigeration is the storage of foods at a
temperature below room temperature, but above
freezing. It is used as a transitional environment. A
transitional environment means that the food product will
ultimately be heated or consumed. It will not stay
refrigerated forever.
 2. Freezing is the storage of food products at
temperatures where water contained in the products
becomes ice. When a food is frozen, it is the water in the
food that freezes. The three main methods of freezing
used in commercial food preservation are:
a. Plate freezing uses the surface of metal plates to
sandwich the food product to be frozen. As the food
and plates contact each other, fluid that circulates in
the plate removes heat and freezes the product.
b. Air-blast freezing uses high speed air and cold
temperatures to freeze the product. Air is the freezing
medium in this method.
c. Liquid freezing involves spraying fluid refrigerants
such as liquid nitrogen on individual food products as
they move down a conveyor belt. This method is
commonly used on meat patties.
 C. Drying—Preservation by drying succeeds because
decay-causing organisms usually do not grow at
moisture contents below 10-15%. Microorganisms need
water for growth and survival.
 1. Drying involves removing the moisture from a food
product. When moisture is removed, most of the
substances that lead to spoilage are also removed. Food
is dried in one of three ways:
a. Mechanical drying uses a machine to remove the
moisture in the food product.
b. Freeze drying involves freezing the food product
then placing it in a chamber where all air and
moisture are removed.
c. Chemical drying uses a chemical substance to
remove moisture from the food. Salt is the most
common chemical used in chemical drying.
 D. Acid—Because of their value as preservatives, and in
some instances their effect as flavor enhancers, certain
organic acids, including acetic and ascorbic acid, are
used to preserve plant products. Microorganisms can
only survive at a specific range of pH values. By
increasing the acidity of the food, the environment
becomes unfavorable for microbial growth.
 E. Oxygen and carbon dioxide—Respiration is directly
affected by oxygen and carbon dioxide levels. Since
respiration is an oxidation process, a reduction in the
amount of oxygen reduces the respiration rate. High
concentrations of carbon dioxide may inhibit or prevent
respiration and may inhibit the ethylene production that
stimulates ripening.
 F. Humidity—In general, low humidity favors desiccation
and wilting. Also, high humidity favors the development
of decay, especially if the temperature is too high.
 G. Fermentation and pickling—The action of certain
bacteria and yeasts in decomposing carbohydrates is
known as fermentation.
1. After decomposition by different organisms, the end
products include carbon dioxide and water (complete
oxidation), acids (partial oxidation), alcohols (alcoholic
fermentation), lactic acid (lactic acid fermentation), and
others. These act as preservatives by retarding
enzymatic deterioration, and they impart flavors that are
regarded as desirable.
2. When the fermentation process is combined
with salting, it is called pickling. Pickling may
be accomplished without the direct use of
microorganisms by placing food in organic acids
(vinegar or citric acid).
3. Citric, lactic, maltic, and tartaric are also
added to foods. All of these acids occur
naturally in plant juices.
4. Fermentation can take place under either of
two conditions: aerobic fermentation takes
place with air present and anaerobic
fermentation takes place without the presence
of air.
 H. Sugar and salt—Sugar is metabolized by
microorganisms, but dissolved molecules of sugar
reduce the activity of water and inhibit the growth of
microorganisms just like dissolved salt. Salt is an
efficient preservative because it reduces water
activity. When bacteria, yeasts, or molds are placed
in a heavy salt brine, water in the cells moves out
(diffuses) through the cell membranes and into the
concentrated brine solution (osmosis). Salt can also
raise the boiling point or lower the freezing point of
water.
 I. Air—With this process, a partial or total vacuum can be
created to prevent aerobic microorganisms from
growing. The storage and handling of fresh fruit and
vegetable commodities must slow the reactions that tend
to break down the product. These degradation reactions
are essentially those resulting from respiration, whereby
the carbohydrates synthesized during photosynthesis
are broken down to carbon dioxide and water.
Procedures that slow or stop the rate of respiration
frequently also slow or stop the rate of deterioration.
Respiration of stored crops can be reduced by limiting
the amount of oxygen.
 J. Irradiation is the exposure of food to gamma rays
generated by a radioactive material.
 1. Gamma Rays have no charge. They are used to destroy
enzymes or microorganisms in the food product.
 2. Food that has been irradiated does not mean that it is
radioactive.
 K. Controlling Air Movement—molds, yeasts, and bacteria
travel through the air. If the movement of air is controlled, the
chances for contamination are minimized. This is one reason
why large food processing machines are covered with lids.
 L. Segregation—every component in food preparation is a
source of contamination. When foods are processed, each
step is separated so that the contaminant does not travel from
one step to the other. Segregation is routine in food
processing plants. Most people are not as careful at home.
The same cutting board may be used to cut different foods
without being washed.
Why are food additives important to food preservation?
 It is almost impossible to eat food that does not contain
preservatives of some kind. Unless you cook all of your meals
from scratch and raise your own food, preservatives are being
consumed.
 A. Additives are used to keep food from spoiling. Food
additives are non-nutritive substances that are added to
foods in small quantities to improve flavor, texture,
appearance, or shelf life. Substances which are not
intentionally added to foods are called food contaminants.
 B. Food additives are chemicals added to a food product to
increase its length of usefulness. The chemicals used are not
dangerous. Instead, they prolong the useful life of the food by
slowing the natural deterioration process.
 C. Food additives can be used for a variety of reasons.
1. Improve the quality of the food.
2. Reduce the amount of waste.
3. Maintain or improve the nutritional value of the food.
4. Improve the shelf life.
5. Increase consumer acceptance.
6. Increase the availability of foods.
7. Make food preparation easier.
 D. Food additives are not the sole solution to food
preservation. Additives are used in combination with
physical and non-chemical methods of preservation.
 E. Companies are responsible for meeting the guidelines set
forth by the US Food and Drug Administration. Other countries
have similar agencies and requirements. Food additives must
meet several strict requirements before they are allowed in
foodstuffs.
 1. It must be safe for humans to consume. Extensive
testing must be completed and validated by the FDA.
 2. The additive must work as indicated in the specified
conditions.
 3. The nutritional value of foods may be not reduced by the
additive.
 4. Customers must not be deceived by the additive and it
must not be used to mask unfavorable ingredients.
 5. A specific method for determining the presence and
amount of must be available.
 6. The additive may not be used instead of good
manufacturing practices.
What are some food additives and how do they help to
preserve foods?
 Food additives fall into a variety of substance
categories. The following table outlines the substance
categories:
 A. Food
Additives
Substance
Categories
 B. The following are examples of food additives:
 1. Monosodium glutamate (MSG) is derived from
seaweed. It has very little taste, but can be used quite
effectively as a flavor enhancer. Additives that have either
no flavor or little flavor, but can improve the flavor of a food
are called flavor enhancers.
 2. Natural or synthetic substances that are used to boost a
flavor or regain a flavor that was lost during processing are
called flavoring agents. Oils, oleoresins, and extracts are
examples of flavoring agents.
 3. Polyols are an example of a texture enhancer. Texture
enhancers not only improve the texture of a food, but they
also improve water retention. Glycerine, mannitol,
propylene glycol, and sorbitol are examples of polyols.
These are found in diet drinks, gum, candy, and ice cream.
4. Many foods contain a variety of metals which are
naturally present. Sequestrants are additives that
combine with these metals helping to inactivate the
metal. Sequestrants prevent the metal ions from
oxidizing with fatty acids resulting in off-flavors. Malic
acid, tartaric acid and citric acid are examples of
sequestrants. They are also antioxidants. They can
prevent oxidative rancidity from occurring.
5. When salt is placed in water, it dissociates into
sodium and chlorine ions. It can thus increase the
boiling point or reduce the freezing point of water.
Osmosis can occur as equilibrium is trying to be
reaching. This creates a lower amount of water present
for microbes to use.
6. Mold growth can be inhibited by sodium or calcium
propionate. The shelf life of bakery products is
increased, but the flavor is not affected.
7. Sorbic acid hinders mold and yeast growth in cheese
and fruit drinks.
8. Sodium benzoate and benzoic acid are used in
candied products.
9. Processed meat products can contain butylated
hydroxyl toluene (BHT) or butylated hydroxyl anisole
(BHA). These antioxidants help to prevent oxidation of
the animal fat.
10. The application of sulfur dioxide allows the fruit or
vegetable to dry faster and destroys the enzymes which
are responsible for browning.
Review/Summary
What is food preservation? How does food
preservation benefit consumers?
What are the methods used in food
science to control contamination?
Why are food additives important to food
preservation?
What are some food additives and how do
they help to preserve foods?