◊ Prevention or delay of microbial decomposition

a) By keeping out microorganisms

b) By removal of microorganisms

c) By hindering the growth and activities of microorganisms

d) By killing the microorganisms

◊ Prevention or delay of self decomposition of food

a) By destruction or inactivation of food enzymes

b) By prevention or delay of purely chemical reactions

◊ Prevention of damages because of insects, animals, human beings and mechanical causes

Methods of food preservation

ο Keeping out of microorganisms

ο Removal of microorganisms

ο Maintenance of anaerobic condition

ο Use of high temperature

i) below 100°C

ii) at 100°C

iii) above 100°C

iv) frying

ο Use of low temperature

i) chilling

ii) refrigeration

iii) freezing

ο Drying

ο Use of chemical preservatives

ο Irradiation

ο Mechanical destruction of microorganisms (Mos)

ο Combination of the above methods (usually two or more)

Wet cleaning is effective in removing firmly adherent soils and in allowing the use of detergents and sanitizers

The method has a number of disadvantages:

♦ It uses large amounts of high quality water which is becoming increasingly costly

♦ Wet surfaces spoil more rapidly

Grading separates the raw materials into categories if different quality.

Grading factors

In general terms, the properties of a food which determine its quality. These are properties controlling:

• Process suitability

• Consumer safety

• Conformity with legal requirement

• Consumer acceptance

There are as many grading standards as there are materials to be graded but grading statements commonly specify the following:

♦ Size and shape: As functional and acceptability factors

♦ Maturity: Freshness of eggs, ripeness in fruit, aging in meat

♦ Texture: Crumb structure in bread and cakes, crispness in celery and apple, viscosity of cream

♦ Flavor and aroma

♦ Freedom from blemish: Cloudy yolks, blood spots or shell cracks in eggs, bruises in fruit, insect holes in coffee beans

♦ Color: As affecting process and consumer acceptance

♦ Freedom from contaminants: Rodent hairs and insects parts in flour, soil and spray residues on fruit, microorganisms and their by products in meat, toxic metals in shellfish etc

♦ Freedom from undesired parts of the raw material: Bone fragments in meat products, leaf or pod residues in peas and beans, stalks or stones in fruit

♦ Conformity with legal standards or codes of practice

Grading Methods:

♦ Procedures in which the quality is determined by laboratory test on samples drown statistically from a batch of food

♦ Procedures which result in the physical separation of the total quantity of the food into quality categories

Sorting separates the raw material into categories of different physical characteristics, such as size, shape and color.

Reasons for sorting:

Sorting plays an important part in controlling the effectiveness of many food processes. Sorted foods have the following desirable attributes

• They are better suited to mechanized operations such as peeling, blanching, pitting and coring

• They are necessary in processes in which uniformity of heat transfer is critical

• They give better control over the weights filled into standard sale container

• In consumer use sorted products are more attractive to the eye and allow the serving of uniformity sized portions. This latter point is of particular importance in catering packs

Types of sorting:

• Weight sorting

• Size sorting

• shape sorting

• Photometric sorting

Food processing is facilitated by the followings:

• Cleaning

• Sorting

• Grading

• Washing

Cleaning

Cleaning separates contaminants from the raw materials.

Functions of cleaning:

• The removal of contaminants which constitute a health hazard or which are aesthetically unacceptable.

• The control of microbiological loads and chemical and biochemical reactions which impair subsequent process effectiveness and product quality.

An acceptable cleaning process must satisfy the following requirement:

• The separation efficiency of the process must be as high as possible consistent with minimum wastage of good material.

• The contaminant must be removed completely after separation so as to avoid re-contamination of the cleaned food.

• The process and equipment should be so designed as to limit re-contamination of the cleaned food.

Cleaning Method

• Dry cleaning method: Screening, brushing, aspiration, abrasion, magnetic separation.

• Wet cleaning method: Soaking, spraying, flotation, ultrasonic cleaning, filtration, settling.