Tuesday, September 8, 2009


Ever since pasteurization came to be established as one of the most widely adopted processing operations known to man for ensuring safety of many liquid foods. It saved millions of lives from dreaded diseases caused by pathogenic microorganisms of high virulence. Even to day billions of liters of fluid milk are being pasteurized for consumption all over the world. Many innovations have taken place to improve the efficiency of the process by cutting down the time and for increasing the shelf life as much as possible. Sterilization which is aimed at complete destruction of all microbes in a system is accomplished by increased exposure to higher temperature to get extended shelf life. Modern process technologies have emerged which can sterilize semisolid foods with assured safety, though canning technology was being used for some semi solid foods which could stand high temperatures. Retort Pouch Technology, so widely used to day for many traditional Indian foods with high viscosity characteristics, is distinguished by specialized equipment system that can ensure faster heat transfer more evenly to achieve commercial sterilization and products can claim shelf lives as much as 12-18 months.

Surgical instruments and medical devices are sterilized using irradiation but this technology is not yet readily accepted by the consumers in many countries. Gamma radiation is still widely used to get rid of pathogens like Salmonella, especially in marine products and meat foods which does not raise the product temperature to any significant extent. For a product like egg which is involved in many food borne illnesses of serious nature, its pasteurization is being insisted on by food safety authorities in many countries. In fact even touching raw eggs is frowned upon because of its potential to spread infection and pasteurized eggs are increasingly becoming standard format for marketing eggs. It is only towards later part of last century that such eggs started appearing in the market. Technologically what are the challenges inherent in pasteurizing a product like egg?

Egg has two distinct components, egg white and egg yolk, both with different physical characteristics and are well separated in distinct compartments in side the shell. Shell has its own physical properties and any system that is intended to impart heat to achieve pasteurization will have to take into consideration this aspect. Egg albumin which makes up the white portion is highly heat susceptible changing its properties due to protein denaturation when heated beyond a certain temperature. Egg melange is a liquid at normal temperature and therefore can be subjected to flash pasteurization under controlled temperature as is being done during spray drying to get egg powder but the dispersibility and foaming properties of egg powder are invariably affected. As for egg in the shell, most of the microorganisms are on the surface and by controlled application of heat most of them can be killed.

Treating with hot water at 56C for 30 minutes followed by drying at controlled hot air can give a relatively safe product with practically no viable cells remaining on the product. How ever a sorting operation is a must to remove those eggs which develop cracks even at this low temperature exposure. Automated plants are now available that can handle as much as one million eggs a day and make them safer for the consumers. Use of Ozone, Hydrogen Peroxide and Microwave heat also are claimed to be effective in achieving pasteurization. While such eggs are accepted without reservation by the consumer for preparing many products at house hold level, processing industry feels that some of the physical properties of the egg are lost which can affect its quality as an ingredient in some formulated products. Almost 4 decades ago Indian food scientists had developed an egg washing powder and an egg coating oil formulation containing permitted bacteriostats and fungistats for sanitizing the egg and extending its shelf life to more than 6 months under low temperature conditions. Probably this development was much ahead of the time with no takers appreciating it. Time has come now to make it mandatory for poultry farms to process the raw eggs before releasing it to the market in the interests of the consumer.


No comments: