Food sterilisation

Sterilisation is a technique to prolong the shelf life of foods.  It is the complete destruction or elimination of all viable organisms in/on a food product being sterilised.

For some canned products they are heated for up to one hour. All micro-organisms are killed during this process. After sterilisation the product is free of germs and, if stored correctly, have a shelf life of several years.

Classical sterilisation treatments are subdivided into two categories: sterilisation by heating (thermal processing) and sterilisation without heating (non-thermal processing).

Thermal processing is widely practiced in spite of some problem such as that the process might reduce nutrition or deterioration the quality of foods.

Non-thermal processes include high pressure processing, pulsed electric fields, ultraviolet radiation, food radiation, chemical treatments, and use of magnetic fields.

Thermal processing is further divided into two categories as in-container sterilisation and aseptic sterilisation.
Food sterilisation

Loss of Quality

Loss of Quality
Just as important as selecting for food quality is the prevention of the loss of quality. The most pervasive problems are probably control of staling and prevention of moisture migration.

Staling as a process is well understood and much progress has been made in understanding how to delay the staling process in wheat flours. However, cooked rice stales and becomes hard within 24 hrs of cooking; arresting the staling process would allow cooked rice of good quality and practicable shelf life to be offered.

Much remains to be understood to control staling so that it can either be stopped when it has reached as desired level or completely inhibited.

Moisture migration limits the shelf life of many products where a high moisture region is in contact with a low moisture region. The manufacturer is unable to give consumer the experience of a fresh baked product.

The pastry is designed to be hard and brittle to contrast with the moist and malleable meat content. Around the meat, a high moisture jelly is injected after baking. Within a few days, moisture migrates from the jelly into the pastry and the case becomes soft, losing flavor and texture contrast with the filling.
Loss of Quality

Factors affecting food shelf-life

The term shelf-life is a finite length of time, after manufacture and packaging, during which the food product retains a required level of quality acceptable for consumption.

In general factors that can affect shelf-life are:
*Product considerations: product description, product packaging, preservatives, shelf-life constraints
*Assembly of product
*Processing
*Hygiene
*Packaging
*Storage and distribution
*Legislative requirement

The factors above will influences the types and levels of microorganisms that will be present and the chemical and biochemical reactions that can occurs, in the final product.

There are several main intrinsic factors that influence most types of spoilage. These factors include raw materials, product formulation and compsoition, temperature, pH, water activity, exposure to oxygen and light, and nutrients or chemicals available in the food product.

Extrinsic factors include:
*Heat treatment
*Headspace gas composition
*Relative humidity (Rh)
*Light (UV and IR)
Factors affecting food shelf-life

Food shelf life

According to one of the most widely accepted definitions, shelf life is a finite length of time, after manufacture and packaging, during which the food product retains a required level of quality acceptable for consumption. 

These expectations are a consequence not only of the primary requirement that the food should remain safe, but also of the need to minimize unwanted changes in sensory quality.

The quality needs are reflected in the labeling requirements to which food manufacturers must conform. 

Quality of foods may be assessed in terms of microbiological numbers, chemical or physical changes in foods, or one of an array of sensory tests of varying complexity.

All foods including raw materials, ingredients and semi manufactured products has its own shelf life and all the subjects involved in the food chain, such as growers, ingredients and packaging suppliers, manufacturers, wholesalers, retailer and consumers have a great impact on it.

Food preservation such as pasteurization and time temperature process extend the shelf life of foods by killing microorganisms or by changing the food and n/or environment conditions to stop or slow their growth. 

The control of water level in foods is an important aspect of food quality as water content affects the shelf life of food.

Freezing and drying are common food preservation processes that are used to extend the shelf life of foods because they render water unavailable for pathogenic or spoilage bacteria.

Shelf life restrictions directly influence scrap rates, out of stock rates in the retail outlets and inventory levels. 

Furthermore, consumers tend to buy the product that has the longest possible shelf life. Being able to offer a longer shelf life than their competitors constitutes a pivotal competitive advantage for food producers.
Food shelf life

Factors influencing the shelf life of food

The most widely accepted definition of shelf life is a finite length, after manufacturing and packaging, during which the food product retains a required level of quality acceptable for consumption.

There are several main factors that influence shelf life and can be divided in two types namely: intrinsic factors and extrinsic factors.

Intrinsic factors are the properties of the final product. They include:
*Raw material
*Water activity
*pH value and acidity
*Redox potential
*Temperature for food
*Available oxygen
*Nutrients
*Physical stress
*Composition of food product
*Product formulation
*Food structure
*Natural microflora and surviving microbiological counts
*Natural biochemistry of the product
*Preservative of the product

While extrinsic factors include:
*Processing
*Raw material preparation
*Relative humidity
*Pressure
*Packaging
*Storage condition and display
*Distribution
*Consumer handling

The shelf life of a food can be altered by changing its composition and formulation, processing parameters, packaging system or environment to which it is exposed.
Factors influencing the shelf life of food

Shelf life of a product

The perception of quality of a product also depends on its form-fresh, frozen, canned or dried. Processing of fruits and vegetables extends the season of a perishable crop. Heat preservation (canning) provides a shelf-stable product, but usually at the cost of color, flavor, and texture. 

Better sensory quality is obtained in frozen foods but at a cost if increased energy requirement to maintain them, in a frozen state. Dried fruit products such as raisins and prunes offer very different attributes than their fresh counterparts. The consumer judges canned products with a different set of criteria than frozen or fresh items of the same commodity. 

Fresh fruits and vegetables are perishable, i.e., they have limited shelf life. They are living, respiring tissue that is also senescing and dying. Certain fruits such as bananas and tomatoes will ripen after harvest, developing desirable color, texture, and flavor during handling and storage. All other fruits and vegetables such as oranges, grapes, cucumbers, and carrots will show little or no improvement in quality within the postharvest system. 

Packing and handling systems have been developed to move the product from farm to consumer expeditiously to minimize quality degradation. Techniques used to extend shelf life of fresh products include 

Lowering the temperature to slow respiration and senescence 

Maintaining an optimal relative humidity to slow water loss without accelerating decay 

Adding chemical preservatives to halt physiological and microbial losses 

Maintaining an optimal gaseous environment to slow respiration and senescence

Longer shelf life can also be obtained by selecting cultivars that are more able to withstand the rigors of the handling system and by harvesting a crop at optimal maturity for storage and handling. 

Shelf life of a product