Food Science

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Unit

• Food Science

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Problem Area

• Handling and Storing Plant Products

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Lesson

• Controlling Molds with Food Preservatives

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Student Learning Objectives

• 1. Describe how different microbes cause food
  spoilage.
• 2. Describe methods used in controlling food
  contamination.
• 3. Explain the methods used in preventing the
  growth of microbes in food.
• 4. Explain methods for decreasing food
  contamination.

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Terms

• aerobic
• anaerobic
• asexual reproduction
• binary fission
• budding
• food additives
• food contamination
• food microbiology

• heterotrophic
• inhibition
• molds
• mesophiles
• parasite
• psychrophiles
• thermophiles

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How do microbes lead to the spoilage of food?

• Food microbiology is the study of certain
  microbes and how they affect food. Microorganisms
  may synthesize compounds that alter the flavor,
  color, or odor of the food product. Fruits and
  vegetables, when they are harvested, are still
  living entities. They are capable of respiration
  and contain substances acted upon by enzymes.
  This enzymatic activity continues to occur even
  after harvest. Ripening and senescence (natural
  aging of plant products through biological
  processes) may occur after harvest, as well as
  deteriorative processes such as browning,
  softening, and oxidation of lipid material.

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• The natural fate of plant material after it dies
  is degradation by microbial action. Microbes are
  tiny organisms that can only be seen through a
  microscope. They depend on their environment to
  provide food. If the environment is favorable,
  the microbes will thrive and multiply. There are
  four important microbes in food science some
  produce favorable results while others can have a
  very negative impact on foods.

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• A. Molds are a form of fungus which is a plant.
  Fungi are organisms that receive their nutrients
  from decaying organisms and can live almost
  anywhere where air and moisture are present.
• 1. Those commonly found on foods reproduce
  asexually. Asexual reproduction means that the
  offspring are formed by simple cell division or
  mitosis rather than sexual reproduction. The
  offspring are genetically identical to the
  parents. Molds produce spores which can be
  carried through the air. As the spores are
  deposited on substances with favorable
  characteristics for temperature, moisture, and
  nutrients a mold colony can develop.
• 2. Molds can be beneficial to food production
  they are used to add flavor and color to cheese
  and in making soy sauces, citric acid, lactic
  acid, and many enzymes. Penicillin and other
  antibiotics are produced with the help of molds.
  Molds can also produce mycotoxins which are
  poisons and are a by-product of mold growth. They
  can be lethal. One example is aflatoxin, which
  can contaminate corn.

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• 3. Molds can grow at extremely low or high
  temperatures and reproduce in acidic or basic
  solutions.
• a. Mesophiles are those molds that grow at room
  temperature (50 F110 F).
• b. Psychrophiles are molds that grow at
  refrigerated temperatures (less than 50 F).
• c. Thermophiles are molds that grow at high
  temperatures (110 F140 F).
• 4. Molds require oxygen in order to survive they
  must live in an aerobic environment or one in
  which oxygen is present. Thus, one of the most
  effective methods of preventing mold growth is to
  store the food product under anaerobic conditions
  or in the absence of oxygen.

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• B. Yeasts are unicellular plants. This means they
  are single-celled. Yeasts are also members of the
  fungi family. They are a unique plant because
  they do not contain chlorophyll. Yeasts live
  mainly on sugars and starches or in high salt or
  sugar environments.
• Yeasts can be used to aid the fermentation
  process. In the case of making bread, beer, and
  yogurt, this is good. In the case of hot dog
  making, the presence of yeast leads to spoilage.
  Yeasts reproduce by budding. A bud or small knob
  forms on the parent cell. The bud grows and
  finally separates or buds from the parent
  producing an identical offspring.

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• C. Bacteria are the most adaptable of all
  microbes and they also are unicellular. The
  bacteria associated with food spoilage are
  heterotrophic. Heterotrophic or heterotrophs
  obtain their nutrients from other organisms
  versus an autotroph which can produce its own
  nutrients. Plants are autotrophs.
• Bacteria can use almost anything as a food source
  and come in a variety of shapes and sizes and are
  thus hard to control. Bacteria reproduce through
  a process called binary fission where the cells
  DNA is replicated and the cell simply splits into
  two identical cells.

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• Some bacteria under favorable conditions can
  reproduce every 20 minutes. One bacteria cell
  reproducing every 20 minutes would result in 17
  million bacteria in only 8 hours. Bacteria can
  also be classified as psychrophilic, mosphilic or
  thermophilic. Bacteria will readily die at a
  temperature of 180F. However, bacterial spores
  which are dormant can live indefinitely at this
  temper-ature.
• D. Viruses are among the smallest forms of life.
  They must be viewed with an electron microscope.
  All viruses are parasites. A parasite is a type
  of symbiosis or relationship where an organism
  lives off of another organism. In the case of a
  virus, it lives off the genetic material of
  another organism.

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What are the methods used in food science to
control contamination?

• Food contamination is the process of a food item
  becoming unfit for consumption due to contact
  with an unclean organism. Preventing
  contamination involves controlling four
  conditions. These conditions relate to both the
  ingredients in the food product and the
  environment where the product is processed.
• A. Controlling Air Movementmolds, 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.

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• B. Segregationevery 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.
• C. Controlling Temperaturemost food contaminants
  are mesophiles (grow at room temperature). For
  this reason, food is rarely kept at room
  temperature for extended lengths of time. Meat
  should be kept refrigerated before it is cooked.
  After it is cooked, it should not be left at room
  temperature for long. Foods should be kept below
  40F or above 140F to prevent bacterial growth.
• D. Controlling Moisture Levelsmost microbes
  thrive in high-moisture environments. High
  moisture environments are common at room
  temperature. This is why food spoils less quickly
  when heated or cooled.

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How can the growth of microbes in food be
controlled?

• Preventing the growth of microbes is secondary to
  preventing contamination. Effective prevention of
  contaminants makes the prevention of microbe
  growth easier. Microbe growth prevention is
  carried out using one of two methods.
• A. Death can be attained using heat or by
  cooling. Processing operations are carried out to
  halt the physiological deterioration and
  microbial action that occurs in fresh fruits and
  vegetables.
• 1. Heat is the most effective and least expensive
  method of killing the microbes.
• 2. Refrigeration destroys most of the microbes.

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• 3. In freezing, extensive cell damage is created,
  which allows deteriorative enzymes to act rapidly
  upon thawing. Blanching (treating with water at
  140 to 150 F) inactivates these enzymes and
  preserves the quality of the product when thawed.
  Rapid cooling after blanching prevents the loss
  of carbohydrates, vitamins, and minerals during
  the blanching process. Fruit that is frozen may
  also be treated with ascorbic acid to retard
  oxidative processes.

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• B. Inhibition is preventing the growth of the
  microbes. It involves altering the environment of
  the microbes so that they cannot thrive. The
  environment may be altered by reducing moisture,
  adding chemicals or changing the pH level of the
  food.
• 1. Food additives are substances added to foods
  during processing to retain or improve desirable
  qualities or characteristics. Processors can add
  sulfur dioxide, potassium sorbate, sodium
  propionate, sodium benzoate, or other additives
  which will inhibit the growth of unfavorable
  microbes.
• 2. Processing Methods can be used to control
  microbial growth. Foods can be canned (heated to
  high temperatures under pressure), frozen
  (destroying enzymes and microorganisms), or dried
  (to decrease moisture levels). The canning
  process not only inactivates enzymes but also
  kills spoilage bacteria. High acid foods such as
  fruits require less heating during canning, since
  high acidity tends to reduce spores of anaerobic
  bacteria.

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How can consumers keep food safe?

• A. Wash your hands and any surface that food
  comes in contact with regularly.
• B. Cold foods should be kept at temperatures less
  than 40F
• C. Hot foods should be kept above 140F
• D. Cooked and raw food should always be kept
  separate. Keep utensils and dishes separate as
  well.
• E. Meats should never be thawed on the counter.
  Use the refrigerator or microwave to thaw them.
• F. Cooking should not be interrupted.
• G. Vegetables and fruits should be washed before
  consumption.
• H. Discard anything that looks suspicious
• I. As a general rule, foods should not be left
  out for more than 2 hours.
• J. Do not use foods that have passed their
  expiration date.

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Review/Summary

• How do microbes lead to the spoilage of food?
• What are the methods used in food science to
  control contamination?
• How can the growth of microbes in food be
  controlled?
• How can consumers keep food safe?