USE OF CHEMICALS IN FOOD PROCESSING

Chemicals used in the preservation of foods belong to a larger group of substances known as food additives. Food additives fall into two broad categories:

  1. Those that prevent food spoilage (eg. preservatives)
  2. Those added to enhance the appearance, flavour or texture of food.



PRESERVATIVES
Many chemicals have been used in the preservation of food for many years.

Techniques include:

  • salting of meat, fish and vegetables,
  • curing of bacon and ham,
  • smoking of meat, vegetables and fish,
  • making jellies, jams, pickles etc.

These use traditional chemical preservatives including smoke, salt, sugars, vinegars and spices.

Sulphur dioxide is the commonest preservative in use, and owes its action to yielding sulphurous acid in solution. Thiamine is rapidly destroyed by sulphites and pork sausages which contain sulphites as a preservative contain much less thiamine than the original pork. Sulphites promote the retention of vitamin C, and their presence in fruit juice and pulp may be regarded as advantageous, apart from their preservative qualities.

At the moment there is considerable doubt about using nitrites and even nitrates in food. Nitrites have been found to be toxic and suspicion has also fallen on nitrates.

The use of chemicals to preserve food is controlled by government regulations in most developed countries.

All preservatives mentioned so far prevent food spoilage caused by microorganisms, and do so by destroying or preventing the growth of the microorganisms as well, in some cases, reducing further attack.

Food spoilage however, may also be brought about by chemical action as when fats, and foods containing fats, go rancid. Rancidity is due to the oxidation of the fats, and the addition of antioxidants to the foods can prevent oxidative changes. Some antioxidants are natural substances (eg. Vitamin E in wheat germ and oily seeds; vitamin C). In addition there are synthetic substances used in baked products such as bread and biscuits.


ADDITIVES FOR ENHANCING APPEARANCE, FLAVOUR AND TEXTURE

The appearance, taste and smell of a food (the organoleptic quality), rather than its nutritive value, determine the appeal of food. The appearance and smell stimulate the flow of digestive juices, and so aid digestion.

When natural colouring of a food is lost or altered during processing, "colouring materials" may be added. Such natural substances as cochineal, saffron, annatto or caramel may be used, as well as such things as paprika, turmeric and sandalwood which will also significantly alter flavour. There have been a number of synthetic colourings (eg. coal tar dyes), but these are not likely to be used because of suspected harmful affects.

FLAVOURING AGENTS form the largest group of food additives, and originally dried herbs & spices (sometimes powdered) were used. These increased palatability for a monotonous diet. Later essential oils, which are much stronger in flavouring power than the original, were extracted from the plant material.

Following the essential oils synthetic flavouring agents were developed. These may be in the form of a solution or powder and prove to be more concentrated, cheaper and far more convenient to use than the corresponding natural flavours. Many are blends of synthetic materials used to imitate the natural flavour more closely.

FLAVOUR ENHANCERS are substances which have no (or only a faint) flavour themselves, but which are able to bring out the natural flavour of foods.

Monosodium glutamate (MSG) is the most widely used flavour enhancer, and is particularly useful in bringing out the natural flavour of meat, fish and vegetable foods. It is added to many canned foods, dried soups etc Some people are allergic to MSG so it should be used with caution. MSG also has a tendency to make people very thirsty.

Ribonucleotides have now been isolated from micro organisms, and are added to processed meat and fish products. Only small quantities are required as their flavour enhancing property is very great, about ten times that of monosodium glutamate (MSG).

SWEETENING AGENTS are used in a variety of foods. The principal one is sugar. While sugar may be in many ways the ideal sweetener, it has disadvantages: it is not sweet enough for certain manufactured foods; it has a relatively high energy value, and in the large quantities now consumed in many countries, it contributes significantly to obesity, dental decay, and possibly coronary heart disease.

Saccharin is the main artificial sweetener used. It is 300 to 500 times as sweet as sucrose, and has no energy value, but it leaves an unpleasant bitter "after taste", particularly after heating. It therefore has limited uses in the food industry.

Cyclamates are one tenth as sweet as saccharin, but have no bitter after taste. Experiments have indicated that both saccharin and cyclamates are safe in foods when used in controlled amounts.

Sorbitol is made from glucose, and hence is related to sugars. It is sometimes added to diabetic foods, because it is slowly absorbed. Its energy value however is similar to glucose, and this must be taken into account in a diet.

Other natural sweeteners sometimes used include honey and molasses.

EMULSIFYING AGENTS AND STABILISERS are added to certain food products containing fat, to form a stable emulsion and enable the more economic use of fat.

Apart from certain natural foods, e.g. eggs, starches, which have some emulsifying or stabilising power, all emulsifiers and stabilisers permitted in food are listed in the Regulations.Of these glyceryl monostearate (GMS) is the most important.It is widely used in the food industry, e.g. in the making of margarine, salad dressing, ice cream and cooking fats.The addition of glyceryl monostearate helps produce a smoother, softer texture in bread-making and helps delay the staling process.

In cake-making it also improves the texture by its stabilising effect on the emulsion, and its shortening power is especially of importance in biscuit making.In both bread and cake-making when emulsifying agents are used there will be a decrease in the fat used.

ANTI-CAKING SUBSTANCES, HUMECTANTS, which absorb moisture and so reduce the effect of humidity and inert gas (nitrogen) used in packaging to minimise oxidation, are food additives used to facilitate processing and to confer properties required ofconvenience foods.


Food Enrichment

Foods may be enriched or fortified by the addition of nutrients.These additions may be statutory under the law or made voluntarily by food manufacturers.

The Bread and Flour Regulations 1963 (Amended 1974) require amongst other things the addition of thiamine, niacin, iron and calcium.(Amounts are given in Study 2).

The Margarine Regulations 1967 require that all margarine be fortified with vitamins A and D.

These additions are made to remedy any possible dietary deficiency of the nutrients concerned and careful consideration has to be given to the quantities added.

In addition to these statutory requirements certain foods are enriched voluntarily by the manufacturers:

(a)Iodine may be added to salt.

(b)Fluorine may be added to water.

(c)Vitamins and mineral elements are added to some breakfast cereals.

(d)Vitamins are added to fruit juices.

(e)Vitamins may be added to baby foods.

(f)Amino acids may be added to some foods.

Goods must satisfy Labelling of Food Regulations in many developed countries.