Food preservation

Food preservation is the process of treating and handling food in such a way as to stop or greatly slow down spoilage to prevent foodborne illness while maintaining nutritional value, density, texture and flavor.

Preservation Processes

Method	Effect on microbial growth or survival
Refrigeration or	Low temperature to retard growth
Freezing	Low temperature and reduction of water activity to prevent growth
Drying, curing and conserving	Reduction in water activity sufficient to delay or prevent growth
Vacuum and oxygen free modified atmosphere packaging	Low oxygen tension inhibits strict aerobes and delay growth of facultative anaerobes
Carbon dioxide enriched modified atmosphere packaging	Specific inhibition of some micro-organisms by carbon dioxide
Addition of weak acids	Reduction of the intracellular pH of micro-organisms
Lactic fermentation	Reduction of pH value in situ by microbial action and sometimes additional inhibition by the lactic and acetic acids formed and by other microbial products. (e.g. ethanol, bacteriocins)
Sugar preservation	Cooking in high sucrose concentration creating too high osmotic pressure for most microbial survival.
Pulsed electric field processing (PEF treatment)	Short bursts of electricity for microbial inactivation
Ethanol preservation	Steeping or cooking in Ethanol produces toxic inhibition of microbes. Can be combined with sugar preservation
Emulsification	Compartmentalisation and nutrient limitation within the aqueous droplets in water-in-oil emulsion foods
Addition of preservatives such as nitrite or sulphite ions	Inhibition of specific groups of micro-organisms
Pasteurization and appertization	Delivery of heat sufficient to inactivate target micro-organisms to the desired extent
Food irradiation (Radurization, radicidation and radappertization)	Delivery of ionising radiation
Application of high hydrostatic pressure (Pascalization)	Pressure-inactivation of vegetative bacteria, yeasts and moulds

Preservation usually involves preventing the growth of bacteria, fungi and other micro-organisms, as well as retarding the oxidation of fats which cause rancidity. It also includes processes to inhibit natural aging and discolouration that can occur during food preparation such as the enzymatic browning reaction in apples which causes browning when apples are cut. Some preservation methods require the food to be sealed after treatment to prevent re-contamination with microbes; others, such as drying, allow food to be stored without any special containment for long periods.

Preservation processes include:

• Heating to kill or denature organisms (e.g. boiling)

• Oxidation (e.g use of sulphur dioxide)

• Toxic inhibition (e.g. smoking, use of carbon dioxide, vinegar, alcohol etc)

• Dehydration (drying)

• Osmotic inhibition ( e.g use of syrups)

• Low temperature inactivation (e.g. freezing)

• Many combinations of these methods

• Chelation

Common methods of applying these processes include drying, spray drying, freeze drying, freezing, vacuum-packing, canning, preserving in syrup, sugar crystallisation, food irradiation, adding preservatives or inert gases such as carbon dioxide.

Other methods that not only help to preserve food, but also add flavor, include pickling, salting, smoking , preserving in syrup or alcohol, sugar crystallisation and curing.

III. Make up different kinds of questions to the text. Ask your partner about the food preservation (Work in pairs or groups)