FOOD SPOILAGE & PRESERVATION
EHVH 441
Food Protection
1. FOOD SPOILAGE
Food must be in the desired state to be considered edible: neither spoiled nor
contaminated; even rats reject bad food! It must have the THREE FREEDOMS from:
1.
Objectionable chemical and physical changes seen and unseen
2.
Contamination and pollution
3.
Biological problems
Therefore, preservation must succeed in:
► Destroying existing pathogens
► Inhibiting growth of surviving microorganisms
► Preventing re-entry of microorganisms and contamination
SPOILED: foods which undergo undesirable change or contain objectionable material.
→Spoiled: organoleptically noticeable damage; compromised quality which
renders food undesirable to eat or inedible: moldy, squishy, discolored, smelly,
obviously rotten. Also under ripe, overripe to point of inedibility
CONTAMINATION / ADULTERATION:
→Contaminated: unsafe, in a potentially dangerous condition due to possibly
invisible bacteria, viruses, parasites, toxins, chemicals, any adulterant, etc.
Chemical
Metals: usually dissolved by the food’s pH
Chemicals, PCBs, PBBs, etc.: accidentally introduced into food
Industrial or cleaning chemicals: usually accidental
Extraneous material
Detritus: miscellaneous things that don’t belong in food e.g., stones
Foreign objects: pieces of machinery/equipment, bolts, wires, glass
Man-made toxicants
Growth enhancers fed to animals or plants to encourage rapid
growth or larger size; diethyl stilbestrol (DES)
Pesticide residues from pest control; Temik (aldicarb) insecticide wrongly used
on watermelons, cucumbers
Antibiotic residues: fed to animals to enhance growth
Additives: approved chemical added to food for a specific purpose, e.g.,
sulfites to extend shelf life
Feeds: prions from sheep parts recycled into cattle feed; cause vCJD
Recycling chicken parts into feed spread salmonella into flocks
Fertilizers: animal waste fertilizers may add fecal bacteria to foods
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BIOLOGICAL PROBLEMS
Biochemical:
Enzymes causing:
Rancidity: breakdown of fat molecules into butyric acid
Autolysis: a food decomposing itself, e.g., shrimp smelling like
ammonia, red meat beginning to rot, smelling, looking slimy
Insect / rodent activity
Gnaw/damage food, packaging
Contaminate with feces, urine, body parts
Consume food needed for humans
Microorganisms & parasites (in relative ascending order of importance in the USA;
variable elsewhere in world)
Microbes:
Yeasts: spoil food; cause off-tastes; a “high” flavor; overt
noticeable colonization of food
Molds: moldy taste, odor, appearance; potentially toxic products
Parasites: capable of infecting humans
Bacteria: rot food; produce infections and toxicants
Viruses: cause human infections
2. SPOILED FOOD IS DETECTED ORGANOLEPTICALLY BY:
A. Sight:
Appearance, color, structure
B. Smell:
Odors
C. Taste:
Flavor changes
D. Texture: Squishy, no longer firm
Laboratory testing may provide objective evidence of spoilage.
3. CAUSES OF FOOD SPOILAGE: OBJECTIONABLE CHEMICAL & PHYSICAL CHANGES
A.
B.
C.
D.
E.
F.
G.
Biological: bacteria, molds, yeast
Enzymes: autolysis (self-digesting e.g., seafood going bad, e.g., crab meat)
Oxidation: produces off-taste, color or odor (cut potatoes, bananas turning brown)
Freezing: turns food either dry or slushy when thawed (crystals break cell walls)
Heating: overcooks and destroys taste and quality
Drying: makes food undesirable
Pressure: crushes, bruises allowing fungi an easy place to colonize
4. FOOD COMPOSITION INFLUENCES THE TYPE OF SPOILAGE AND THE RATE OF CHANGE
A. Carbohydrates: sugars, starches ferment, turn bitter and emit gas, vinegar
B. Proteins: amino acids decay into cadaverine, ptomaines, saurine
C. Fats: complex lipids turn “rancid” but usually very slowly
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5. ENVIRONMENTAL CONDITIONS AFFECTING SPOILAGE
A.
B.
C.
D.
Nutrients
Inoculum and growth curve
Water activity = AW
Oxygen reduction potential
E.
F.
G.
pH
Temperature
Inhibitors
define potentially hazardous foods
affect lag phase length
moisture available for microbes to use
determines whether aerobic or anaerobic growth
is possible
acid, near neutral, or alkaline may control rate
<32oF, <41oF, >140oF
preservatives, e.g., sodium benzoate
6. FOOD SPOILAGE AND FOODBORNE ILLNESS PRINCPLES
A. Environmental conditions affecting spoilage equally affect pathogens.
B. If food is spoiled by microbial action, it is also possible that foodborne
illness-causing bacteria, if present, would grow and multiply.
C. Absence of evidence is not evidence of absence; i.e., absence of obvious spoilage
does not assure that food is free of FBI-causing pathogens or toxins, and safe.
7. Food preservation = prevention of spoilage
Stopping food spoilage by preservation techniques is stopping the action of
biological agents (bacteria, yeast, molds), autolytic enzymes and oxidation without
detracting from foods’:
1. Wholesomeness
2. Acceptability
3. Nutritive value
8. PRESERVATION METHODS
A. Heat:
1.
2.
3.
using high temperatures (adding heat)
Pasteurization -- limited heat treatment: 174°F / 20 seconds; 280°F / 2 sec.
Boiling
Canning -- achieving commercial sterility: the destruction of all pathogens and
spoilage organisms in the food but NOT ALL LIFE, e.g., some spores survive.
PROBLEM: if underprocessed and spoilage organisms (normally spore formers)
are not destroyed in canning, spoilage inside cans may produce:
a. Flat sour = acid formed but no gas (no swelling)
b. Springer = acid formed and minimal gas produced (one end swells)
c. Sweller = acid and gas formed (both ends swell)
PROBLEM: if underprocessed, some canned or otherwise packaged (reduced
oxygen packaged (ROP) foods can support Clostridium botulinum organisms
and cause botulism.
CODE NUMBERS stamped on the lid of canned foods and other packaged
foods allow for fast identification, tracebacks and recalls.
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B. Cold: using low temperatures (removing heat)
1. Refrigeration at 32o - - 38oF
►Does not kill
►Reduces or stops organisms’ multiplication rate
2. Freezing <32oF /0°C
Lethal to some parasites if temperature low enough and if held for long
enough time
C. Fermentation: sugars →acids (pH is the limiting factor)
D. Reduce available moisture (lower the water activity = Aw)
1. Drying
2. Smoking
3. Osmotic pressure: sugar/salt
4. Freeze drying
E. Chemical preservation
1. Smoking
2. Sodium benzoate
3. Nitrites
4. Sulfites
F. Oxygen exclusion
Remove, reduce or simply exclude O2 or replace it with N2
1. Canning in glass, plastic or metal
2. Reduced Oxygen Packaging (ROP)
3. Air-tight shrink wrap plastic
G. Ultra-high pressure
Up to 111,000 psi (16 million lbs/ft2) pressure against microorganisms
H. Irradiation
1. Limited to specific foods: primarily chicken, fruits, vegetables, and spices, ground
beef.
• Level of X-ray or gamma radiation exposure is restricted to useful level.
2. Irradiation is most effective in destruction of insects and their eggs; trichina
worms; stopping potato, onion sprouting, and extending shelf life.
• Ineffective against viruses, prions.
3. CONCERN: chemical changes that occur in some foods from radiation treatment
may result in the production of unique, possibly harmful radiolytic products.
• Public fear #1: some unknown but potentially carcinogenic radiolytic products
may be formed.
4. CONCERN: Quality control: taste and texture problems. High doses ruin
palatability.
5. CONCERN: public acceptance. Fear of the “R” word.
9. PACKAGING
A. Protection of foods from contamination after processing
B. Retain quality and safety produced by processing
C. Concern: migration of chemicals in the packaging materials into the food
D. Concern: creation of hazardous microenvironments for bacterial growth
E. Extend shelf life (maintain freshness)
F. Maintain pleasing appearance and induce customers to buy
3 Food Spoilage and Preservation HO.doc
11/13/09
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