Briefing Paper from the British Nutrition Foundation
Food processing includes any action that changes or converts raw plant or animal materials into safe, edible, and more palatable foodstuffs. Food processing also provides us with the means to extend the shelf life of otherwise perishable foods. Without food processing it would not be possible to sustain the needs of modern urban populations, and the choice of food available would be very limited and largely seasonal. Changing lifestyles and family structures have resulted in a largely consumer-led demand for an ever-growing selection of foods, particularly ready-prepared and partially prepared products.
Virtually all foods undergo some form of processing before they are ready to eat. At its most simple, processing can be peeling a piece of fruit or boiling potatoes. The oldest, traditional methods of food processing include sun-drying, smoking, pickling and salting. These methods utilise the fact that water removal increases shelf life. Fermentation and freezing are also very traditional methods. Canning, pasteurisation and sterilisation are techniques that have been used for many decades but are still important techniques in the modern food processing industry. However, they are now being joined by many new processes, and a number of others are already waiting in the wings.
One of the key factors that has stimulated the availability of a diversity of products is consumer interest in health and related issues, such as ‘naturalness’ and ‘added value’. This interest has led to the development of products that are lower in fat, sugar and/or salt and higher in fibre, and products that have specific vitamins or minerals added to them. The addition of nutrients to foods and drinks is used around the world as a public health measure and as a cost effective means of ensuring the nutritional quality of the food supply. The addition of nutrients requires careful attention to food regulations, a suitable nutritional rationale and that the final product remains acceptable to consumers.
A recent example of this approach, in the UK, is the voluntary addition of folic acid to bread and breakfast cereals as a means of increasing the folate status of women of childbearing age. This has been stimulated by recognition that low folate status is associated with an increased risk of neural tube defects. Vitamin and mineral fortification is common in Britain, and many foods are fortified to some extent. In some cases the addition of micronutrients is mandatory, e.g. fortification of margarine with vitamin A and vitamin D, whereas in the majority of cases it is voluntary, e.g. the addition of a range of vitamins and minerals to breakfast cereals.
Food processing can improve the nutritional value of certain foods. For example, severe heat treatment destroys trypsin inhibitors, which are anti-nutritional factors present in a range of foods. Prolonged boiling also destroys the harmful lectins present in legumes, such as red kidney beans. Food processing can also increase the bioavailability of nutrients in foods and the organoleptic qualities of foods. On the other hand, however, any form of food processing, even slicing, washing and cooking foods in the home, can result in a loss of heat sensitive, oxygen sensitive and light sensitive nutrients, especially certain vitamins. Leaching of vitamins and some minerals into the cooking water can also occur with vegetables.
The main commercial processes that cause nutrient loss are blanching, heat processing, and drying or dehydration. However, in some cases, processed foods actually retain more nutrients than the unprocessed form. The best examples are frozen vegetables, which are picked and frozen within hours of harvest, whereas ‘fresh’ vegetables may have been stored for several days before purchase or use. Even with unprocessed vegetables, however, modern storage and transportation techniques can help retain nutrients.
An example of a potential health concern arising from food processing involves trans fatty acids. Vegetable oils are often hydrogenated to improve their oxidative stability and functional properties, e.g. during the manufacture of margarine, and during this process trans fatty acids (a group of unsaturated fatty acids) can be produced. It is thought that trans fatty acids behave more like saturated fatty acids than unsaturated fatty acids after ingestion. However, the general consensus in the UK is that current intakes of trans fatty acids do not present a problem.
Many new processing techniques have been developed in response to changing nutritional concepts and consumer demand for less processed foods e.g. ohmic heating and high intensity pulsed electric field processing. Such processes are sometimes called non-thermal processes or minimal processing techniques. The objective is to produce high quality, safe foods that are convenient, fresher and considered more natural. The nutritional implications of some of the techniques that are still in development have yet to be established and will almost inevitably determine whether or not these techniques achieve commercial success.
Functional foods are the latest refinement in a continuum of products developed to provide ‘added value’. One commonly used definition of a functional food is: ‘a dietary ingredient that affects its host in a targeted manner so as to exert positive effects that may, in due course, justify certain health claims’. Within this context, there is increasing interest in prebiotics, probiotics and synbiotics. Prebiotics are substances, e.g. oligosaccharides, that are not digested but which beneficially affect the host by selectively stimulating the growth of specific bacteria in the colon. It is now recognised that the composition of the bacterial population of the large bowel is important for human health, and can potentially be manipulated by the type of food eaten. Another approach to influence the gut microflora involves the incorporation of live micro-organisms (probiotics) into foods, such as yogurts. A third approach, the use of synbiotics, is a combination of the above two approaches.
The use of genetic modification in food production is a relatively new process and has many potential applications. For example, a plant can be modified to resist disease, microbial attack or insect infestation, or to produce fruit with a better flavour and improved keeping qualities. Plants can also be developed to resist certain herbicides that are applied to kill weeds. Other possibilities include drought resistance (very important in developing countries) and resistance to fruit damage. The use of genetic modification offers substantial potential benefits to the food industry and consumers, but it is recognised that some consumers may have reservations about this new and unfamiliar technology. To help in the recognition of foods which contain genetically modified material, regulations have recently been published that require all foods containing ingredients produced from genetically modified soya or maize to be labelled, except when neither protein nor DNA resulting from the genetic modification is present in the food itself.
© British Nutrition Foundation