With the beginning of civilisations and human settlements, the consumption of food by the human population increased and thus, the need to preserve excess foods became essential for survival. Since then, many traditional and household methods of food preservation have evolved to limit food spoilage. Such as cooking, the addition of spices and fermentation.
In modern commercial food production, spoilage and contamination are preserved by a variety of methods.
1. Filtration:
Microorganisms can be removed from the water, wine, beer, juices, soft drinks and other liquids by filtration. Several major brands of beers are filtered rather than pasteurised to preserve the flavour and aroma of the original product.
2. Dehydration and freeze drying:
Dehydration, such as Lyophilisation to produce freezing dried foods, is a common method of eliminating microbial growth. It is especially effective for vegetables and pasta.
3. Refrigeration:
Refrigeration temperatures (typically -2°c to 16°c) slows microbial growth but can’t eliminate microbes completely. Thus, it is only used to preserve food for shorter periods and generally used for household purposes.
4. Vacuum Packing:
Food can be packed under vacuum or under atmosphere with decreased oxygen or increased carbon dioxide level. For example, carbon dioxide storage is particularly effective for extending the shelf life of Apples.
5. Pasteurisation:
Pasteurisation involves heating food to a temperature that kills disease-causing microorganisms and substantially reduces the levels of spoilage organisms with minimal effect on food value and texture. For example, milk is commonly pasteurised at 63°c for 30 minutes followed by quick cooling to 4°c.
6. Canning:
Canning is most widespread and effective means of long-term food storage. In canning, food is cooked under pressure to attain a temperature high enough to destroy endospores (around 121°c). After heat treatment, the cans are cooled as rapidly as possible, usually with cold water. The main drawback of canning is that the quality of food is sometimes compromised, particularly that of liable biochemicals such as vitamins.
7. Microbial Product–Based Inhibition:
Bacteriocins are bactericidal proteins active against closely related bacteria, which bind to specific sites on the cell, and affect cell membrane integrity and function. The only currently approved product is Nisin. It is nontoxic to humans and affects mainly gram-positive bacteria, especially Enterococcus faecalis. Nisin can be used particularly in low-acid foods to improve inactivation of Clostridium botulinum during the canning process or to inhibit germination of any surviving spores.
8. Irradiation:
Exposure to ionising radiation, known as food irradiation, effectively sterilises many kinds of food for long-term storage. The main concerns about food irradiation are its potential for unknown effects on food chemistry and the hazards of irradiation during human involvement in the process.
9. Organic Acids as Preservatives:
Organic acids commonly used to preserve food include benzoic acid, sorbic acid, and propionic acid. The acids are generally added as salts such as sodium benzoate, potassium sorbate, sodium propionate. They work best in foods that already have moderate acidities (pH 5-6), such as dried fruits and processed cheeses.
10. Inorganic Compounds as Preservatives:
Inorganic food preservatives include salts, such as phosphates, nitrites, and sulphites. Nitrites and sulphites in inhibit aerobic respiration of bacteria, and their effectiveness is enhanced at low pH. Current concern about nitrite arises from the observation that it can react with amines to form carcinogenic nitrosamines.
11. Other organic compounds:
Numerous organic compounds, both traditional and synthetic, have antimicrobial properties. For examples, Cinnamon and Cloves contain the benzene derivative eugenol, a potent antimicrobial agent.
References:
Books:
- Prescott, Lansing M, John P Harley, and Donald A Klein. Microbiology. Dubuque, IA: McGraw-Hill Higher Education, 2005. Print.
- Pelczar, Michael J, E. C. S Chan, and Noel R Krieg. Microbiology. New York: McGraw-Hill, 1993. Print.
- Slonczewski, Joan, and John Watkins Foster. Microbiology. New York: W.W. Norton & Co., 2009. Print.