FOOD SPOILAGE & FOOD PRESERVATION

 

Foods undergo deterioration or spoilage from the time they are harvested, slaughtered, or manufactured. Foods undergo physiological, chemical, and biological changes & make them unfit for human consumption.

Numbers of causes are responsible for food deterioration. These include:

• Micro-organisms

• Activities of enzymes present in food

• Insects

• parasites

• rodents

• temperature

• moisture

• Oxygen, light, and time

 

These factors are not isolated in nature. At any one time, many forms of spoilage may take place depending upon the food and environmental conditions.

• Micro-organism: bacteria, yeasts & moulds spoil food after harvesting, during handling, processing & storage. The micro-organisms are found everywhere & are always present to invade the flesh of animas & plants. When there is a cut in their skin or if the skin is weakened by disease or death.

• Food enzymes: enzymes present in plant & animal foods continue to be present and are even intensified after harvest & slaughter. Enzymes are responsible for facilitating many changes during storage such as changes in colour, texture and flavour e.g. ripening of tomatoes, tenderizing of meat on ageing are desirable, but if proceeded too far can result in food spoilage if not halted at the

 

 

•                 appropriate time. The enzymes need to be inactivated by suitable method at appropriate time to prevent food spoilage.

• Insects, parasites & rodents: insects are destructive to cereals grains, fruits & vegetables. The loss of food due to insects’ destruction varies from 5-50% depending upon the care taken in the field & storage. Insects are generally controlled by fumigation with ethylene oxide & propylene oxide. Parasitic food spoilage occurs in some foods. Pigs eat uncooked food waste; the parasitic nematode penetrates the pig’s intestine & finds its way into pork. The live worms can infect man if the pork is not thoroughly cooked. Entamoeba histolytica is responsible for amoebic dysentery. This organization contaminates food when raw human excreta are used as fertilizers for crops. Infected water and poor hygiene also spread the parasites. Cooking kills most of these parasites. Rodents contribute substantially to food spoilage rats cockroaches rodents urine and drippings harbour several kinds of disease producing bacteria and rats spreads such human disease as typhus fever, plague, typhoid fever etc.

• Temperature: - Heat and cold contribute to food spoilage if not controlled. The rate of chemical reaction doubles itself for every 10o C rise in temperature. Excessive heat brings about protein denaturation, destroy vitamins, break emulsions and dries out food by removing moisture. Freezing and thawing of fruits and vegetables destroy their structure.

• Moisture: - Foods with high % water spoil fast. Perishable foods have a high-water content. Control of moisture in foods is thus very important. From the point of view of their preservation.

• Oxygen, Light and Time: - air and oxygen bring about several changes in food components such as destruction of food colour, flavor vitamin A & C and other food constituents. Oxygen is to be excluded from in the course of processing while deareation, vacuum packing or flushing containers with nitrogen or carbon dioxide. Light destroys vitamin B2, A and C. it also deteriorates many food colours. Foods may be protected from light by impervious packing or keeping them in containers that screen out specific wavelengths. Food’s spoilage is time dependent. The larger the time, the greater the destructive influences.

• Food Safety in The Home: - in order to avoid food spoilage in the home, standards of hygiene should be maintained. Personal hygiene & kitchen sanitation practice should be maintained.

 

SPOILAGE OF CEREALS AND CEREAL PRODUCTS

The exterior of harvested grains retains some of the natural flora plus contamination from soil, insects & other sources e.g.

• Of bacteria that infested Pseudomonadaceae, micrococcus, lactobacillus.

• Washing & milling reduces microorganisms.

• Blending & conditioning increases contamination.

 

Cereal products

• Wheat flour – bacteria – bacillus, sarcina, micrococcus, moulds – aspergillus, penicillium.

• Corn meal – moulds – fusarium, penicillium.

• Bread – a freshly baked loaf is practically free of viable microorganisms, but mould spores contaminate during cooking & before wrapping slicing by knives also contaminates.

 

MILK AND MILK PRODUCTS

• Milk contains few bacteria when it leaves the udder of healthy cow.

• Contamination starts from the animal especially the exterior of the adjacent areas. Bacteria found in manure, soil & water may entre from this source.

• Microorganisms from milking machine, when milking by hand.

• Contamination from dairy utensils & milk contact surfaces like milk oil or milking machines, bulk milk cooler.

• Hands & arms of the milker, flies, the air around milk parlour.

• Other sources tanker-truck, transfer pipes, sampling utensils, separators, homogenizers, coolers, glass bottles.

 

MILK PRODUCTS

• BUTTER: - microorganisms from churner, from water used in its washing, old cream & packaging material.

• Dry milk, evaporated milk & sweetened condensed milk may be contaminated from special equipments used in their preparation.

• Cheese – it is contaminated from air, brine, tanks, shelves & packaging material.

• Ice cream – organisms may be added to ice cream in the ingredients.

 

MEAT

The healthy inner flesh meat contains few or no microorganisms although they have been found in lymph nodes, bone marrow & even flesh. Normal slaughtering practices would remove the lymph nodes from edible parts. Contamination comes from external sources during bleeding, handling, and processing. During bleeding, skinning, and cutting the main sources of microbes is the exterior of the animals (hide, hoofs, and hair) and the intestinal tract.

• Knives, clothes, air, hands, and clothing of the workers can serve as intermediate source of containments.

• During handling contamination comes from cart, boxes, and contaminated meat, from air and from personals.

• Grinders, sausages stuffers, slicing, casing and ingredients are the sources.

• In home refrigerators, containers used previously to store meats act as a source.

 

E.G., moulds – Cladosporium,  geotrichum, penicillium. Bacteria – pseudomonas, bacillus, clostridium.

EGGS: - Most freshly laid eggs are sterile but the shells of some become contaminated by faecal material from the hen, by the lining of the nest, by wash water, by handling the materials in which eggs are packed.

FRUITS AND VEGETABLES

• Spoilage occurs during storage, transportation while waiting to be processed, washing, mechanical damage, processes such as trimming, peeling, cutting, coring add to contamination.

 

CANNED PRODUCT

Spoilage occurs by chemical, biological or both.

• CHEMICAL: - by hydrogen swell resulting from the pressure of hydrogen gas released by action of acid of goods on the iron of the cane, time, temperature of storage, tinning imperfection, poor exhaust etc.

• BIOLOGICAL: - by microorganisms, survival of organisms after administration of the heat treatment, leakage of the container after the process permitting the entrance of microorganisms.