Food Safety Focus (6th Issue, January 2007) – Food Safety Platform
Preservatives in Food
Reported by Mr. Johnny CHU, Scientific Officer,
Risk Assessment Section, Centre for Food Safety
Food is a perishable commodity. If not kept properly, it may support growth of a variety of microorganisms such as bacteria, yeasts and moulds. The growth of these microorganisms causes spoilage of food. Occasionally, pathogenic microorganisms and/or their toxic secretions may also be present in food, consumption of which may lead to harmful effects on human health.
Preserving techniques to keep food fresh or palatable have a very long history. Since ancient times, it has been necessary to keep supplies of harvested food edible over unfavourable periods such as winter, rainy periods and drought. As such, a number of preserving methods had been invented to cope with the need. These include boiling, drying, smoking, salting and the use of preservatives.
What are Preservatives?
Preservatives serve as antimicrobials which prevent or slow down the growth of moulds, yeasts and bacteria. In Middle Ages, saltpetre was used to preserve meat. Nowadays, nitrite, the active ingredient in saltpetre, is used for curing bacon and ham. Benzoic acid, sulphur dioxide, sorbic acid and propionic acid are other examples of preservatives. Some of these chemicals are natural. For example, benzoic acid is a natural constituent in plums, cranberries and cloves and propionic acid occurs naturally in some cheeses.
Table 1: Some common preservatives, their primary functions and applications
| Preservatives | Target Organism(s) | Examples of Application(s) in Food |
|---|---|---|
| Sulphite | Yeasts and bacteria | Dehydrated fruits and vegetables, sausages |
| Nitrite | Bacteria | Bacon |
| Propionic acid | Moulds | Bread |
| Sorbic acid | Moulds | Cheeses, wines |
| Benzoic acid | Yeasts and moulds | Soft drinks, ketchup |
By preventing the growth of moulds, yeasts and bacteria, preservatives can improve the safety of food as well as prevent the wastage of seasonal surplus by making it last longer on the shelf or in the fridge.
Are Preservatives Safe?
All preservatives must go through rigorous safety assessment and approval procedures. They are permitted for food use only when they are proved to present no hazard to the health at the level of use proposed.
Although many allergic reactions to foods are caused by natural food ingredients such as milk, fish and peanuts, some are caused by food additives such as sulphur dioxide. Sulphur dioxide is used as preservative in a wide range of foods, in particular soft drinks, sausages, dried fruits and vegetables.
Nitrite is mainly used in sausages, ham, bacon and pickled meat to inhibit the growth of Clostridium botulinum. Accidental intake of large amount of nitrite can cause a kind of blood disorder called methaemoglobinaemia. Ingested nitrite, in the presence of protein substances in the stomach, may form N-nitroso compounds, which have been shown to be probable human carcinogen and may increase the risk of stomach cancer. Nitrite also occurs naturally in food like cereals and vegetables.
If consumers have balanced diets, exposure to a specific chemical will be lowered and so is the risk.
Some consumers are still concerned about the safety of some preservatives such as nitrite and sulphur dioxide. To address their concern and enable those who may be allergic to specific preservatives to identify and avoid them, the presence of food additives (i.e. including preservatives) in prepackaged food available in Hong Kong must be identified by their names or identification numbers on the label of the food after July 2007.
How are Preservatives Regulated in Hong Kong ?
The Preservatives in Food Regulations, Cap. 132BD (the Regulations) stipulate which preservatives are permitted for food use and their maximum levels in specified foods . At present, there are a total of 12 permitted preservatives and 91 specified foods in the Regulations.
The Centre for Food Safety (CFS) is currently reviewing the Regulations and has issued a consultation paper on the subject. The consultation paper and details of public consultation forums are available at the CFS website .