Food Spoilage

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