UNIT 3 - FOOD SPOILAGE AND FOOD PRESERVATION

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

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

1. Micro-organisms
2. Activities of enzymes present in food
3. Insects
4. parasites
5. rodents
6. temperature
7. moisture
8. 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

TYPES AND CAUSES OF SPOILAGE

1. Micro-organism:

 Bacteria, yeasts & molds spoil food after harvesting, during handling, processing & storage. The micro­ organisms are found everywhere & are always present to invade the flesh of animals & plants, when there is a cut in their skin or if the skin is weakened by disease or death.

2. 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 flavor 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.

3. Insects, parasites & rodents:

Insects are destructive to cereal 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.
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.

5. Temperature

Heat and cold contribute to food spoilage if not controlled. The rate of chemical reaction doubles itself for every 10° 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.

6. 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.

7. Oxygen,  Light and Time

Air and oxygen bring about a number of 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 deareat ion, 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. Foods spoilage is time dependent. The larger the time. the greater the destructive influences .

SOURCES OF CONTAMINATION

1. Contamination from the Source

Meat, raw veggies, eggs and milk can be contaminated with e-coli, salmonella or other food borne pathogens before they even reach the processing plant. These products are exposed while in or on the ground through contact with animal feces, bacterial infection, and contaminated ground water. According to the Center for Disease Control and Prevention, eggs are often contaminated before they are deposited by the hen, through salmonella present in the hen’s ovaries.

2. Contact in Pre-Processing

Slaughterhouses are notorious for co-mingling meats before and after slaughter, thus causing contamination. Contact with pathogens can also occur during transit, when the food is sitting idle in the back of a hot truck. Improperly cooled or heated food only heightens the problem. Food that only contains a few microbes can become a teaming piece of bacterial heaven after sitting in transit for a few hours.

3. Problems During Processing

Contamination during processing involves environmental contaminants like metal shavings, pesticides and chemicals used to operate and maintain the machinery. Contamination can occur from improper maintenance, improper use of the machines and breaches in the ventilation system that leads to the processing area.
Most contaminants can be defeated after processing with high heat or freezing. Other types of contamination's requires immediate disposal of the food.

Spoilage of different food products

Spoilage of Cereals and Cereal Products

The exterior of harvested grains retain some of the natural flora plus contamination from soil, insects & other sources e.g.
Washing & milling reduces microorganisms.
Blending & conditioning increases contamination.
Cereal products
Wheat flour - bacteria
Corn meal - molds
Bread - a freshly baked loaf is practically free of viable microorganisms, but mold 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 enter 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 .
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 stutters, slicing, casing and ingredients are the sources.

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 occur 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 can, 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.

Basic principles of food preservation

In accomplishing the preservation of foods by the various methods the following principles are involved: -
Prevention or delay of microbial decomposition.

• By keeping out microorganisms.
• By removal of microorganisms.
• By hindering growth activities of microorganisms.
• By killing of microorganisms i.e. by heat or radiation.

Prevention or delay of self decomposition of the food:-

• By destruction or inactivation of food enzymes e.g. by blanching
• By prevention or delay of chemical reaction

Prevention of damage because of insects animals and mechanical causes

Methods of food preservation

1. Asepsis or keeping out microorganisms.
2. Removal of microorganisms.
3. Maintenance of anaerobic conditions.
4. Use of high temperature.
5. Use of low temperature.
6. Drying
7. Use of chemical preservatives
8.  Irradiation
9. Mechanical destruction of microorganisms by grinding or high pressure.
10. Combination of two or more of above methods.

1. ASEPSIS:  - keeping out the microorganisms by adopting good hygienic  practices  and sanitized environment.
2. REMOVAL OF MICRO-OGANISMS: - can be done by filtration, centrifugation (sedimentation or clarification) washing or trimming.
3. MAINTENANCE  OF ANAEROBIC CONDITION: - a complete fill, evacuation of unfilled space or replacement of air by carbon dioxide and by inert gas nitrogen.

PRESERVATION BY USE OF HIGH TEMPERATURE

• High temperatures denature proteins and inactivate enzymes required for metabolisms of the microorganisms.
• The treatment varies with microorganisms. Depending on the heat treatment employed some of the vegetative cells, most of the cells are part of bacterial spores, or all of them may be killed.
• Yeast and yeast spores: are killed at 60°C for 10 to 15 minutes
• Mold & mold spores: Are killed at 60°C in 5 to 10 minutes
• Bacteria: salmonella - 60°C for 4 minute
• E.coli - 57.3°C for 20 to 30 minutes, streptococcus thermophiles - 70°C to 75°C for 15 minutes, clostridium botulinium -   100°C for 100 to 330 minutes.

PRESERVATION BY USE OF LOW TEMPERATURE

• Low temperatures are used to retard chemical reactions and action of food enzymes and to slow down or stop the growth and activity of microorganisms in foods.
• The lower the temperature the slower the chemical reaction, enzyme action and microbial growth.
• A low enough temperature will prevent the growth of any microorganisms.
• Commercial refrigeration temperatures i.e. lower than 0°C to 7°C effectively retard growth of many food borne pathogens.
• Cold storage: - most commercial lstorage freezers are at or below - 18°C.
• Common or cellar storage lower than 15°C (for root crops,potatoes. cabbage, apples)
• CHILLING STORAGE: - it involves cooling by ice or by mechanical refrigeration. Most perishable foods including eggs,dairy products, meat, sea food,vegetables & fruits are kept at chilling storage. Temperature varies from – 0.5°C to 10°C.
• FROZEN STORAGE:  -
• Sharp freezing:  -15°C to -29°C & may take 3 - 72 hours.
• Quick freezing:
• Direct immersion of the food or the package food in a refrigerant as in the freezing of fish in brine.
• Indirect contact with the refrigerant at -17.8°C to -45.6°C.
• Air blast freezing where air at - 17 .8°C to -34.4°C is blown across the materials being frozen.

PRESERVATION BY DRYING

• Drying usually is accomplished by the removal of water but any method that reduces the amount of available moisture in a food is a form of drying.
• Method of drying includes
• Solar drying ( raisins, figs, pears, fish, rice)
• Mechanical dryers - it involves passage of heated air with controlled relative humidity over the food to be dried or the passage of the food through such air. E.g. evaporator or kiln, drum dry, spray drying, freeze dryers & vacuum dryers.

PRESERVATION BY FOOD ADDITIVES
A food additive is a substance or mixture of substances, other than the basic food stuff, which is present in food as a result of any aspect of production, processing, storage or packaging.
Those food additives which are specifically added to prevent the deterioration or decomposition of a food are referred as chemical preservatives, their enzymes activity or their genetic mechanisms. E.g. propeonic acid,

PRESERVATION BY RADIATION
Use of UV radiation
Ionizing radiation which include x rays, gamma rays, beta rays and cathode rays and microwave heating which have electromagnetic waves between infrared  and radio waves.