Food Deterioration and its Causes

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Food Deterioration and its Causes
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Main Idea

• What is food deterioration, and how can food
  science minimize its effects?

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Food deterioration includes

• changes in organoleptic quality (how something is
  perceived by a sensory organ)
• nutritional value
• food safety
• aesthetic appeal
• color

• texture
• flavor

• To some degree, all foods undergo deterioration
  after harvest.
• The role of food science is to minimize negative
  changes as much as possible.

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CATEGORIES OF DETERIORATION

• occurs when a food is consumed that contains a
  chemical toxic to humans. Staphylococcus aureus
  and Clostridium botulinum produce toxins. Molds
  in foods produce mycotoxins like aflatoxin that
  are not destroyed by heat.

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Insects

• Insect damage can be minor, but this wounds the
  tissue for additional damage by microorganisms.
• Controls for insects include pesticides, inert
  atmosphere and cold storage.

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The three general categories of food
deterioration are

• Physical
• Chemical
• Biological
• Factors that cause food deterioration include
  light, cold, heat, oxygen, moisture, dryness,
  other types of radiation, enzymes,
  microorganisms, time, industrial contaminants and
  macroorganisms (insects, mice, and so on).

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Table 1. Useful ShelfLife at 70 F

• Food Days
• Meat 1 to2
• Fish 1 to 2
• Poultry 1 to 2
• Dried, smoked meat 360
• Fruits 1 to 7

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Table 1. Useful ShelfLife at 70 F

• Food Days
• Leafy vegetables 1 to 2
• Root Crops 7 to 20
• Dried seeds 360

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SHELF LIFE AND DATING OF FOODS

• There is a time limit for the usefulness of all
  foods. This time limit depends on the type of
  food, the storage conditions and other factors.
  If food is held at about 70 F (21 C) its useful
  life varies as shown in Table 1.

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SHELF LIFE AND DATING OF FOODS

• Shelf life is the time required for a food
  product to reach an unacceptable quality. This
  length of time depends on the food item (Table
  1), the processing method, packaging and storage
  conditions. Food manufacturers put code dates on
  their products. "Pack date" is the date of
  manufacture. The date of display is called the
  "display date," and the "sell by date" is the
  last day to sell. Some foods have a "best used by
  date," or the last date of maximum quality. The
  "expiration date" indicates when the food is no
  longer acceptable.

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WHAT CAUSES FOOD DETERIORATION?

• Specific causes of food deterioration are listed
  below. Deterioration can be caused by one or more
  of the following
• Microorganisms such as bacteria, yeast and molds
  
• Activity of food enzymes
• Infestations by insects, parasites and rodents
• Inappropriate temperatures during processing and
  storage
• Gain or loss of moisture
• Reaction with oxygen
• Light
• Physical stress or abuse and
• Time.

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Bacteria, yeast, mold

• Thousands of species of microorganisms exist, and
  a few hundred are associated with foods. Not all
  are bad in fact, some are desirable in food
  preservation. Microorganisms are found in the
  soil, water and air on animal skins, plant
  surfaces and digestive tracts but they are
  usually not present in healthy tissue.
• Bacteria are single-celled organisms occurring in
  three shapes round (cocci), rod (bacilli) and
  spiral (spirilla and vibrios). Some produce
  spores which are resistant to heat, chemicals and
  other adverse conditions.

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Bacteria, yeast, mold

• Yeasts are the largest of the microorganisms but
  are still single cells, and some produce spores.
• Molds are larger than bacteria. They are often
  filamentous and they all produce spores.
• In foods, these microorganisms attack basically
  all the food components -- including sugars,
  starches, cellulose, fats and proteins. Depending
  on the food and the microorganism, the action on
  food could be to produce acids, making the food
  sour, or to produce alcohol. Some microorganisms
  produce gas, making the food foamy, while others
  produce unwanted pigments or toxins.

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Bacteria, yeast, mold

• Environmental conditions that affect microbial
  growth include temperature and oxygen. Microbes
  that prefer cold temperatures are said to be
  pyschrophilic. Mesophilic microorganisms prefer
  normal temperatures, while thermophilic
  microorganisms prefer hot temperatures. Bacteria
  or molds that require atmospheric oxygen are said
  to be aerobic, while those yeasts and bacteria
  that do not require atmospheric oxygen are called
  anaerobic. Facultative microorganisms are
  adaptive, and can survive in either aerobic or
  anaerobic conditions. Obligative microorganisms
  are capable of survival in only one or the other
  situation.

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Foodborne disease

• Humans may be infected by eating a food
  containing a microorganism. Infections can be
  caused by Clostridium perfringen, Salmonella sp.,
  Escherichia coli (E. coli 0157) and several
  others. Food intoxication

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Food enzymes

• All foods from living tissues have enzymes. Most
  of these enzymes will survive harvest or
  slaughter. At the time of harvest or slaughter,
  enzymes that control digestion and respiration
  proceed uncontrolled and cause tissue damage.
  Some of the post-harvest enzymatic reactions are
  actually desirable, as in the ripening of
  tomatoes and the aging or tenderizing of beef.
  Enzyme action can be controlled by heat,
  chemicals and radiation.

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Heat and cold

• Normal harvest temperatures range from 50 to 100
  F. The higher the temperature, the faster
  biochemical reactions occur. In fact, the rate of
  chemical reactions doubles with each 10 degree
  rise in temperature. On the other hand,
  sub-freezing temperatures damage tissues. Cold
  temperatures may also cause discoloration, change
  the texture, break an emulsion and denature
  protein. Chilling can injure the tissue of fruits
  as well.

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Oxygen

• Chemical oxidation reactions can destroy vitamins
  (especially A and C), alter food colors, cause
  off-flavors and promote the growth of molds.

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PRINCIPLES OF FOOD PRESERVATION

• Food preservation involves the use of heat, cold,
  drying (water activity or Aw), acid (pH), sugar
  and salt, smoke, atmosphere, chemicals, radiation
  and mechanical methods.

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Heat

• Most bacteria are killed at 180 to 200 F, but
  spores are not. To ensure sterility, you must
  have wet heat at 250 F for 15 minutes. High acid
  foods require the same temperature of heat for
  less time.

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Cold

• Most microbial growth slows at temperatures under
  50 F. Some bacteria, called psychrophiles,
  actually thrive at relatively low temperatures
  and will continue slow growth. Foods frozen at
  less than 14 F usually do not have any free
  water, so these foods also benefit from low water
  activity to help protect against microbial
  growth. Freezing may kill some but not all of the
  microorganisms.

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Drying

• Drying reduces the water activity (Aw) in a food.
  Since microorganisms contain about 80 percent
  moisture, drying or dehydrating the food also
  dehydrates the microorganism. Changing the amount
  of water in a food also alters the rate of enzyme
  activity and other chemical reactions.

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Acid

• As the food becomes more acid (lower pH) the heat
  required for sterilization is reduced. For
  example, the pH of corn is about 6.5. At 226 F,
  15 minutes are required to destroy C. botulinum
  spores. The pH of pears is about 3.8 and only 5
  minutes are necessary to destroy C. botulinum at
  226 F. Acid may occur naturally in foods, be
  produced by fermentation or be added
  artificially.

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Sugar, salt and smoke

• Sugar, salt and smoke are chemical means of
  controlling food deterioration. The addition of
  sugar or salt to a food item increases the
  affinity of the food for water. This removes the
  water from the microorganism through osmosis.
• Smoke contains formaldehyde and other
  preservatives. The heat involved with adding the
  smoke helps reduce the microbial populations and
  it dries the food somewhat.

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Atmosphere

• Changing the storage atmosphere reduces food
  deterioration. The growth of aerobes is slowed by
  removing the oxygen, while providing oxygen
  limits the growth of anaerobes. Adding carbon
  dioxide or nitrogen also slows deterioration.

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Chemicals

• Chemical additives such as sodium benzoate,
  sorbic acid, sodium or calcium propionate and
  sulphur dioxide retard the growth of
  microorganisms, modify enzyme activity, inhibit
  chemical reactions or modify the structure of
  foods

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Radiation

• Radiation includes X-rays, microwave, ultraviolet
  light and gamma rays. Radiation can destroy
  microorganisms and inactivate enzymes.

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Food Sanitation

• Definition
• protection from contamination
• Must include
• all functions
• operations
• Food products
• Ongoing / Dynamic (ever changing)
• Sanitation is a Way of Life

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Temperature Control

• Food Temperatures
• Danger zone (40ºF to 140ºF)
• Thermometers
• Monitor temperatures
• Thawing

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Hygiene and Personnel Practices

• People are the 1 consideration
• Rules
• Setting
• Following
• Breaking

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Hygiene and Personnel Practices

• Sanitation program is an attitude
• Willingness
• Effort
• Ongoing training

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Hygiene and Personnel Practices

• Personnel Training
• Appropriate sanitation principles
• Food handling practices
• Manufacturing controls
• Personal hygiene practices

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Sanitation Principles/Food Handling

• Training
• Should instill understanding of processing steps
• Technology for each product
• Where problems exist
• Desire to satisfy consumers
• Guard consumers interests

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Manufacturing Controls/Essential Operations

• Personnel
• Must be trained in critical elements
• Importance of these operations
• Monitoring these operations
• Action to be taken
• Certification Programs
• Ex. Heat processing equipment
• Develop specific training programs

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Hygienic Practices

• Communicable diseases/ Injuries
• Hand Washing
• Personal Cleanliness/ Conduct

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Communicable Diseases

• Restricted access for
• People known to carry or suffer from transmitted
  diseases through food
• Restricted from any food-handling areas
• Persons afflicted with
• Infected wounds
• Skin infections
• Sores
• Open cuts
• Completely covered
• Secure
• waterproof

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Hand Washing

• Facilities
• Hot water hand washing station
• Convenient to food handling area
• Personnel
• Wash hands with soap
• Warm running, potable water
• Must be washed
• After handling contaminated materials
• Using toilet facilities
• Disinfectant hand dips

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Personal Cleanliness/Conduct

• Must be maintained in food handling operations
• PPE
• Sanitary clothing
• Hair covering
• Footwear
• Properly maintained PPE
• Gloves
• Remove all jewelry
• Tobacco, gum, and food are not permitted

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EXERCISES

• 1. Read the labels on food in your home, in a
  grocery store or on items you buy during the day.
  Make a list of the date codes on five different
  foods. List the "sell by date," the "best used by
  date," and the "expiration date" for as many of
  the foods as you can. Discuss these in class.

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EXERCISES

• 2. Leave a food such as meat, bread, fruit and so
  on at room temperature and describe the changes
  in food quality. Discuss these with the class and
  try to categorize the changes and their causes.

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EXERCISES

• 3. Why is the occurrence of E. coli 0157 in food
  such a worry?

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EXERCISES

• 4. What is the chemical makeup of enzymes and how
  many enzymes exist?