When food is available more than the present use, it is preserved for future consumption. Foods gradually undergo deterioration or spoilage from the time they are harvested, slaughtered, or manufactured.   Some foods spoil rapidly like (leafy vegetables, fruits, milk, meat etc.) and other keep for longer but limited periods. 

• Food preservation techniques have a long history of its use. It was probably first practiced soon after our ancestors developed from hunter-gatherer society to initiate primitive farming producing food surpluses and then necessitating extended storage to avoid wastage.
• Food preservation is the technique to prevent food spoilage, food poisoning, and microbial contamination.
• It is known “as the science which deals with the process of prevention of decay or spoilage of food thus allowing it to be stored in a fit condition for future use”.
•  Any of several methods by which food is kept from spoilage after harvest or slaughter. Such practices date to prehistoric times. The technologies that were used the most were drying, curing, fermentation, and cooking.
• Modern methods include canning, pasteurization, freezing, irradiation, and the addition of chemicals. Advances in packaging materials have played an important role in modern food preservation.

Why Food Preservation?

1. Reduces food waste

2. Ensures food safety

3. Extends shelf life

4. Maintains nutritional value

5. Supports global food security

6. Enhances flavour and texture.

Food Spoilage

Food spoilage means the original nutritional value, texture, and flavour, of the food are damaged, the food becomes harmful/ unfit for human consumption.

 These changes may be caused by various factors, including contamination by microorganisms, infestation by insects, or degradation by endogenous enzymes (those present naturally in the food).

 Types and reasons of food spoilage

1.       Physical Spoilage

Physical damage to the protective outer layer of food during harvesting, processing or distribution increases the chance of chemical or microbial spoilage.

 Examples of physical spoilage include

·         Staling of bakery products and components

·         Moisture migration between different components

·         Physical separation of components or ingredients

·          Moisture loss or gain

2.       Chemical Spoilage

When animal or vegetable material is removed from its natural source of energy and nutrient supply, chemical changes begin to occur which leads to deterioration in its structure.

The two major chemical changes which occur during the processing storage of foods and lead to a deterioration in sensory quality are lipid oxidation (rancidity) and enzymic browning. Chemical reaction also is responsible for changes in the colour or flavour of foods during processing and storage.

3.      Microbial  Spoilage

These microorganisms ( moulds,  yeasts, and  bacteria ) do not cause diseases but they spoil food by growing in the food and producing  substances which alter colour,  texture,  and odour of the food, making it unfit for human consumption.

For example souring of milk, growth of moulds on bread and rotting of fruits and vegetables.

a)      Yeast:  Yeast-growth Causes fermentation which is the result of yeast metabolism.

 There are 2 types of yeasts true yeast and false yeast.

True yeast metabolises sugar producing alcohol and carbon dioxide gas this is know as fermentation.

False yeast:  Yeast grows as a dry film on food surface such as  on pickle brine, False yeast occurs in food that have high sugar and high acid environment.

b)      Moulds

Moulds grow in filaments forming  a tough mass which is visible as  “mould growth”

Moulds form spores which, when dry, float through the air to find suitable conditions when they can start the growth of cycle again.

Moulds  can cause illness, especially if the person is  allergic to molds. Usually though, the main symptoms of eating  mouldy foods will  be nausea or vomiting from the bad taste and smell of the mouldy food.

Both yeasts and moulds can thrive in the high acids food like fruit tomatoes, jams, jellies and pickles. Both are easily destroyed by heat.

 Bacteria  (fungal spoilage):

These are the most harmful of the all microorganisms. These are the microscopic organisms and are found in the large numbers.  Slight acidic and nitrogenous foods are best for the growth and multiplication. The bacteria are too resistant to different operations.

                                                                                                             Bacteria are round, rod or spiral shape microorganisms. Bacteria may grow under a wide variety of conditions. There are many types of bacteria that cause spoilage. They can be divided into spore forming and non spore forming. Bacteria generally prefer low acid foods like vegetables and meats. Eating spoiled food caused by bacteria can cause food poisoning.

Enzyme Spoilage

Enzymes are proteins found in all found in a small in all plants of animals. If uncooked foods are not used while fresh, enzymes cause undesirable changes in colour,  texture and flavour, Enzymes are destroyed easily by heat processing.

These chemical substances play a remarkable role in changing the state of fruits and vegetables. Enzymes are chemicals that make the rapping process of fruits and vegetables complete, but if their activity is not checked properly, they spoil and cause final decay.

 Enzymes change starch into sugar, and protein into amino acids and thus constituents of food are changed. This action can easily be controlled by regulating the temperature exclusion of moisture and air. Some fruits when cut, change the colour of flesh it is due  to the reaction of atmosphere with enzymes.

Millard browning or (Non Enzymic browning)

This is browning reaction which occurs during the roasting, baking, grilling, and frying of many foods. It’s just some chemical reaction between amino acid and (protein) and reducing sugar (carbohydrate), usually requiring heat.

Brown coloured compounds are formed which are responsible for the attractive colours of products such as bread crust, roasted meat, fried potatoes and baked cakes & biscuits.

Enzymic Browning

When the cells of some fruit (like Apple’s Pears, bananas, peaches, avocado)  and vegetablrs (like potatoes) are cut and exposed to the air enzymes present in the cell bring about  an oxidation reaction, colourless compound are converted into brown-coloured compounds.

Rancidity

Most fats and oil do not store very well, they develop off flavours and odours known as rancidity. Rancidity is important when considering the self-life of food products.

It caused by several factor:

·         Absorption rancidity

·         Oxidative rancidity

·         hydronic rancidity

a.       Absorption Rancidity: When oils fats are stored next to strong smelling foods ( e.g. onions and garlic ) or product  (e.g. paints, detergents, and disinfection) the smell is absorbed by a fat or oil making it unpleasant to eat.

b.      Oxidative Rancidity: Oxygen from the air can oxidize unsaturated fats producing objectionable flavours.  This is the most important and common type of Rancidity.

Anti-oxidants used to prevents the development of rancidity agent used as remove the oxygen e.g. BHA is one of thepermitted Anti-oxidants added to fat, vitamin E is antioxidant present naturally in many fats and oils.

c.       Hydrolytic Rancidity:This is the caused by the presence of water, which cause triglycerides to split into glycerol and fatty acids. The rate of hydrolysis in the presence of water along is negligible but hastens if enzymes (lipases) and microorganisms (bacteria moulds, and yeasts) and present. It results in the formation of free fatty acid and Soaps (salt and free fatty acid). The oil/fats develops a soapy taste/texture. This isa less common type of rancidity but is a quite common emulsion such system such as butter, margarin and cream.

                                     High temperatures, the presences of  moisture, oxygen light  are among the factors that speed up rancidity.

Most vegetables  oil deteriorates  slowly, animal fats deteriorates quicker and marine (fish) oils which contain very high proportion of highly unsaturated fatty acid) deteriorate so rapidly that they are useless for edible purposes and unless they are refined hydrogenated.

Other factors

·         Oxidation

Air: Atmospheric oxygen can react with some components which may cause rancidity or color changes.

·         Low Temperature Injury: The internal structure of the food damage very low temperature.

·      Light and Time: Light destroys vitamins A, and C.  It also deteriorates many foods colours. Further all the deteriorative changes time dependent. Larger the time greater will be the destructive effects.

·         Moisture: Presence or absence of excess moisture in food leads to spoilage. Moisture is required for chemical reaction and microbial growth. Foods with high moisture content will deteriorate as faster rate.