Food Deterioration and Its Control

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Chapter 7

• Food Deterioration and Its Control

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• All foods undergo deterioration after harvest to
  some degree
• Role of food sciences is to minimize negative
  changes to the extent possible

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Deterioration Includes Changes In

• Organoleptic quality
• Nutritional value
• Food safety
• Aesthetic appeal
• Color
• Texture
• Flavor
• Etc.

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Categories of Deterioration

• Physical
• Chemical
• Biological

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Factors Causing Deterioration

• Heat
• Cold
• Light
• Other radiation
• Oxygen Moisture
• Dryness

• Enzymes
• Microorganisms
• Macroorganisms
• Industrial contaminants
• Time

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Useful Life (in days) at 21oC
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Shelf Life

• Time required for a food product to reach
  unacceptable quality
• Depends on
• food item
• processing method
• packaging
• storage conditions

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Food Dating

• Types of Code Dates
• Date of manufacture (pack date)
• Date of display (display date)
• Last date to sell (sell by date)
• Last date of minimum quality (best used by
  date)
• No longer acceptable date (expiration date)

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Major Causes of Food Deterioration

• Growth activity of microorganisms
• bacteria
• yeast
• molds
• Activity of food enzymes
• Infestation by
• insects
• parasites
• rodents

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• Inappropriate temperatures
• during processing
• during storage
• Gain or loss of moisture
• Reaction with oxygen
• Light
• Physical stress or abuse
• Time
• Combinations of any/all of the above

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Bacteria, Yeast, Mold

• There are 1000s of species of microorganisms
• A few hundred are associated with foods
• Some are desirable in food preservation
• Found everywhere
• Soil, water, air
• Animal skin, plant surfaces, digestive tracts
• Usually not inside healthy tissues

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Bacteria

• Bacteria single-celled organisms
• Round (cocci)
• Rod-shaped (bacilli)
• Spiral (spirilla and vibrios)
• Some produce spores
• Spores dormant condition resistant to heat,
  chemicals, and other adverse conditions

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Mold

• Larger than bacteria
• Are often filamentous
• All produce spores

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Yeast

• Largest of the microorganisms
• Single cells
• Some produce spores

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Microorganisms attack

• Basically all food constituents
• sugars
• starches
• cellulose
• fats
• proteins

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Microorganisms produce

• Acids (makes food sour)
• Alcohol (gives you a buzz)
• Gas (foamy)
• Pigments (gives color to foods)
• Toxins (causes food poisoning)

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Environmental Conditions Affecting Microbial
Growth

• Temperature
• psychrophilic lt16oC
• mesophilic 16-38oC
• thermophilic gt38oC
• Oxygen
• Aerobic (some bacteria, all molds)
• Anaerobic (some bacteria, yeast)
• Facultative (both with and without oxygen)
• Obligative (either with or without oxygen)

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Food-Borne Disease

• Food infection
• Microorganism must be present in the food and
  will set up infection in humans
• Food intoxication
• Food contains a chemical which is toxic to humans

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Food Intoxication

• Staphylococcus aureus and Clostridium botulinum
  produce toxins
• Molds produce mycotoxins (ex aflatoxin)
• Toxins often are not destroyed by heat (cooking)

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Food Infection

• Clostridium perfringens, Salmonella sp., and
  several others including Escherichia coli (strain
  0157H7)

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Insects Parasites

• Damage 5-10 of the US grain crop
• Insects can cause minor damage, but wound tissue
  allowing for further microbial damage
• Control
• Pesticides
• Inert atmospheres
• Cold storage

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Acceptable Levels of Fly Eggs Larvae in Tomato
Products
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Food Enzymes

• All foods from living tissues contain enzymes
• Most of these enzymes willsurvive harvest and/or
  slaughter
• At the time of harvest or slaughter, enzymes
  which control digestion/respiration proceed
  uncontrolled and cause tissue damage

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Controlling Enzymes

• Inactivation by heat
• Chemicals
• Radiation
• Some post-harvest enzymatic reactions are
  desirable (i.e. ripening of tomatoes,
  aging/tenderizing of beef)

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Heat Cold

• Normal harvest temperatures range from 10-38oC
• The higher the temperature, the faster the
  biochemical reactions
• Rate of chemical reactions double with each 10oC
  rise in temperature
• Sub-freezing temperatures damage tissues

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Examples of Cold Damage

• Discoloration of tissues when frozen
• Changes in texture when frozen
• Milk emulsion will be broken
• Milk protein will denature and curdle
• Chill injury can occur near freezing, esp. in
  tropical fruit tissues (ex banana)

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Oxygen

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

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Principles of Food Preservation

• Heat
• most bacteria are killed at 82-93oC, but spores
  are not
• 121oC wet heat for 15 minutes is required to
  ensure sterility
• high acid foods require less heat
• in milk, only disease-causing organisms are
  killed to reduce the severity of heat required

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Principles of Food Preservation

• Cold
• under 10oC, microbial growth is slow
• psychrophiles will continue slow growth
• frozen food (lt-10oC) usually does not have any
  free water
• frozen food also benefits from low water activity
  to help protect against microbial growth
• freezing may kill some, but not all
  microorganisms, but growth is slowed or stopped

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Principles of Food Preservation

• Drying
• microorganisms contain approx. 80 moisture
• dehydrating food also dehydrates the
  microorganisms

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Principles of Food Preservation

• Acidification
• acids may be in foods naturally, produced by
  fermentation, or added artificially
• as pH decreases, heat required for sterilization
  is reduced

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Time Required to Destroy C. botulinum Spores
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Sugar Salt

• Addition of either to a food item increases the
  affinity of the food for water, thereby removing
  water from the microorganism through osmosis

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Smoke

• Contains formaldehyde and other preservatives
• Heat will help reduce microbial populations and
  somewhat dries the food

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Atmosphere

• Exclude air (O2) for control of aerobes
• Provide air (O2) for control of anaerobes
• Add CO2
• Add N2

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Chemicals

• Sodium benzoate
• Sorbic acid
• Sodium or calcium propionate
• Sulfur dioxide

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Radiation

• X-Rays
• Microwaves
• Ultraviolet light
• Gamma Rays
• etc.