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Food Spoilage. What is Food Spoilage. Spoilage is a natural phenomenon. It occurs at varying rates depending on the storage temperature, kind of food involved, kind of microorga- nisms present, packaging materials used, food additives used and method of preservation. - PowerPoint PPT Presentation
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Food Spoilage
What is Food Spoilage
Spoilage is a natural phenomenon. It occurs at varying rates depending on
the storage temperature, kind of food involved, kind of microorga- nisms present, packaging materials used, food additives used and method of preservation.
Spoiled Food can be defined as any food that is not acceptable to an individual or group because of health hazard or aesthetic appeal.
The period of time between the manufacture
and the retail purchase of food is called the
Shelf Life.
During this time a food product has a
satisfactory quality in terms of nutritional
value, taste, texture and appearance
Food categories
Stable or Nonperishable Foods
Semi-perishable Foods
Perishable Foods
PRE-HARVEST DETERIORATION
10-20% AGRICULTURAL COMMODITIES ARE LOST
•WEEDS•INSECTS•MICROORGANISMS•RODENTS•BIRDS
Conditions Leading to Food Decay
EXTERNAL CONDITIONS PRODUCT CONDITIONS Storage temperature Initial quality Humidity Raw material Gas O2, N2, CO2 Ingredients
Packaging materials Intrinsic factors Light Hygienic Processing
BIOCHEMICAL/CHEMICAL DECAY MICROBIAL DECAY Rancidity Putrid flavor WOF Sour taste Changes in texture Slime, Gas Discoloration Off-flavors Loss od nutrients Formation od toxic substances Changes in texture
Causes of Food Spoilage:
Senescence
Microbial decay
Chemical deterioration (enzymatic &
non-enzymatic)
Physical deterioration; desiccation.
Insects and rodents
SENESCENCE
•FRUITS & VEGETABLES CONTINUE TO RESPIRE AFTER HARVEST LEADING TO DETERIORATION
•CATABOLIC REACTIONS IN MEAT & FISH
Enzymatic spoilage
Enzymes are chemicals produced by all livingthings. They help speed up or slow down chemical reactions, act as transports for foods, and are a normal constituent of foods. For instance, as a banana matures, the color changes from green to yellow to brown to black. The change is caused by the enzymes (chemicals) in the banana. The ripening, then softening, of other fruits such as apples, peaches and tomatoes is another example of enzymatic action.
Enzymatic spoilageEnzymes can be inactivated by heat, which is thereason for blanching vegetables; or they can beinactivated by cold temperatures below 40 degreesF, which is the reason for placing vegetables underrefrigeration. Think of green tomatoes in therefrigerator compared to tomatoes sitting on thewindow sill.
Bacteria also produce enzymes that breakdown food and allow them to obtainnutrients through their cell walls. Therefore,lowering the temperature reduces the rate ofenzyme action as well as the rate at whichbacteria can multiply.
Examples:
In corn and pea: simple sugar starch
In vegetables and fruits phenol + O2 brown products
In butter fat hydrolysed fat
Physical Deterioration & Dessication
• PHYSICAL/MECHANICAL ABUSE CAUSES RELEASE OF ENZYMES INTO TISSUES• CRUSHING, BREAKS IN THE SKIN (FRUIT/ VEGETABLE) LEAD TO MICROBIAL INVASION• WATER/MOISTURE LOSS DURING STORAGE• WATER/MOISTURE UPTAKE • RETROGRADATION OF STARCH• MELTING OF FOOD
Microbial Decay
Bacteria
Yeasts
Molds
Viruses
BACTERIA
• GROW THE FASTEST• REPRODUCE BY CELL DIVISION:• VEGETATIVE CELLS (actively metabolizing cells, consume nutrients and produce waste products)• SPORES (dormant form of the bacterial cell)• BASIC SHAPES: • COCCI (CIRCULAR SHAPE) • RODS (LENGTH IS GREATER THEN WIDTH) • MOTILE RODS (FLAGELLA)
Yeasts ; MoldsYEASTS
• COMMONLY FOUND IN MANY FOODS• GROWTH IS SLOWER• TOLERATE SEVERE ENVIRONMENTAL CONDITIONS (pH, aw)• SOME ARE USED TO PRODUCE FERMENTED FOODS
MOLDS
• FILAMENTOUS FORM• FOUND IN MOST FOODS• TOLERATE HARSH ENVIRONMENTAL CONDITIONS (pH, aw)• SOME USED IN FERMENTED FOODS• AGENTS OF FOOD SPOILAGE• PRODUCE TOXINS (MYCOTOXINS)• PRODUCE SPORES
AEROBES GROW ONLY IN THE PRESENCE OF O2
ANAEROBES GROW ONLY IN THE ABSENCE OFO2
FACULTATIVE ANAEROBE CAN GROW IN THE PRESENCE/ABSENCE OF O2
BACTERIA: Aerobes, anaerobes, facultative anaerobes YEASTS are facultative anaerobes MOLDS are strictly aerobes
MICROORGANISMS CAN BE CHARACTERIZED ON THE BASIS OF OXYGEN REQUIREMENTS
Conditions Necessary for Microbial Decay
Microbial spoilage is the major cause of food spoilage. It occurs as a result of contamination of food by microorganisms, provision of a suitable environment for their growth, and degradation of the foodstuffs.
To control microbial build up, you must control:
• The source of microorganisms - people, raw materials,equipment, air currents, dust and pests.
• Food residues, which are required for bacterial growth
Conditions Necessary for Microbial Decay
• Moisture is required for growth; thus relative humidity should be monitored. • Time during which food product is exposed to a given set of conditions that promote bacterial growth. • Temperature determines the kind of microorganisms.
Microbial Growth Curve
A-B lag phaseB-C phase of positive accelerationC-D exponential phaseD-E phase of negative accelerationE-F stationary phaseF-G accelerated death phaseG-H death phaseH-I survival phase
The best way to prevent microbial food decay is to lengthen:
The lag phase
The phase of positive growth
This can be accomplish by:
Reducing the amount of microbial contamination as much as possible
Avoiding the addition of actively growing organisms
Microbial decay can be prevented by:
Keeping out microorganisms
Removal of microorganisms
Hindering the growth or activity of microorganisms
Killing the microorganisms
Self-decomposition of food can be prevented by:
by destruction or inactivation of food enzymes
by prevention or delay of purely chemical reactions
Classification of food preservation methods based on major controlling factors
high temperature
low temperature
removal or tying up moisture
addition of chemical preservatives
keeping microorganisms out
ionizing radiation (irradiation)
The kinds and numbers of microorganisms present on or in food depends on:
The kind and extent of contamination
Previous opportunities for the growth of certain kinds
Pre-treatments which food has received
Factors affecting microbial growth
Associative Growth: Antibiotic, Symbiotic, Metabiotic
Environmental Conditions:
Physical State of Food
Chemical State of Food
Temperature
Chemical Changes caused by microorganisms:
Changes in nitrogenous organic compounds.
Anaerobic decomposition of proteins, peptides and amino acids that result in production of obnoxious odorous is called Putrefaction.
Changes in carbohydrates:
Alcoholic fermentation
Lactic fermentation
Mixed lactic fermentation
Coliform type fermentation
Propionic fermentation
Butyric-butyl-isopropyl fermentation
Changes in organic acids
Changes in lipids
Other changes
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