Food Safety Focus (40th Issue, November 2009) – Food Safety Platform
Food Processing Technology to Minimise Food Hazards
Reported by Ms. Waiky WONG, Scientific Officer,
Risk Assessment Section, Centre for Food Safety
In ancient days, without knowing the science behind, people tried ways to keep food for a longer period, such as drying of food and use of sugar or salt, which formed the foundation of food processing technology for extending the shelf-life nowadays.
Factors Causing Food Deterioration
Almost all foods would undergo deterioration after harvest, and, as a result, sensory and nutritional quality and food safety would be affected. Many factors, such as temperature, water activity * , oxygen, microorganisms, enzymes, light and time, would affect the rate of food deterioration. Food preservation is an important food processing technology to help minimise such negative changes in order to produce safe and quality food for consumers.
Food Preservation Methods
Food preservation methods include heat treatment, cold storage, drying, the use of acid, sugar and salt, the use of chemicals, controlled- or modified-atmosphere storage, and radiation, and in a large extent, they can be applied in combinations, to control factors causing food deterioration, as well as to minimise food hazards.
Heat treatment is applied to destroy microorganisms in food, under various time and temperature combinations, in which pasteurisation and sterilisation are the two most common ones for destroying the pathogenic microorganisms, and the pathogenic microorganisms and spores, respectively. In addition, food undergone sterilisation can keep for a longer time under ambient condition. For example, some milk and juice products requiring refrigeration are products that have undergone pasteurisation (e.g. milk is heated at least 72 ° C for at least 15 seconds), while canned food and ultra high temperature (UHT) milk or drink products are products that have undergone sterilisation (e.g. milk is heated at least 132 ° C for at least 1 second).
Illustration: Pasteurised milk and UHT milk
Cold storage including refrigeration and freezing is used to retard the growth of microorganisms, rather than destroy them. In some cases, food after pasteurisation (e.g. pasteurised milk) should be kept refrigerated or frozen, in order to maintain the food safety and quality.
Drying is a process for removing water from food and as such it reduces the water activity in food for inhibition of the microbial growth and enzyme activity. The conventional drying process involves the use of heat, however, the sensory and nutritional quality would be affected. To better retain the sensory and nutritional quality, a modern drying process – freeze drying is applied to reduce water activity without heating the food, in which the food is first frozen and then water is evaporated from ice without the ice melting under vacuum condition. It is commonly used in production of dried fruit and vegetables.
The Use of Acid, Sugar and Salt
The heat required for sterilisation is reduced in food with a lower pH (i.e. acidic) (usually pH < 4.6). Acid may be present in food naturally, produced by fermentation or added artificially. The addition of sugar or salt would reduce the water content in food through osmosis.
The Use of Chemicals
Food additives are added in food to maintain or improve quality of food, for example, preservatives (e.g. sodium benzoate, potassium sorbate) are added in food to retard the growth of microorganisms.
Controlled- or Modified-atmosphere Storage
Control or modification of the storage atmosphere surrounding a food could reduce food deterioration and also inhibit microbial growth. It can be done by removing the oxygen or adding carbon dioxide or nitrogen. It is most commonly used for storage of fruits and vegetables after harvest.
Radiation is a relatively new method for food preservation to destroy the microorganisms and inactivate enzymes in food, in which ionising radiation and microwave are forms of radiation being applied in food preservation. To enable readers to have a better understanding on these newer methods, we are going to discuss more about the use of ionising radiation and microwave to reduce food hazards in the coming issues.
* Water activity is a value to describe the availability of water in food for microbial, enzyme or chemical activity.