Fibre sources for the food industry.

Few issues in human nutrition have captured popular attention in the way that dietary fibre has in recent years. The hypotheses of Burkitt et al. (1972), coupled with the considerable body of new knowledge which has been accumulated over the last decade or so, have led to a general consensus that the consumption of dietary fibre should rise significantly, and there is a very widespread awareness and acceptance of this view amongst consumers. The recommendations of the National Advisory Committee on Nutrition Education (1983) in this context were that average intakes should rise from 20 g fibre/d to about 30 g fibre/d (with fibre as defined by the Southgate method (Southgate, 1976)), and that this increase should come largely from high-extraction cereals. Similar, though less precise, recommendations have recently been published in the USA as part of The Surgeon General's Report on Nutrition and Health (1988). As Southgate (1988) has pointed out, it is very difficult to obtain this substantial increase in dietary fibre from a Western mixed diet unless it contains significant quantities of high-extraction cereal products. Such foods must through necessity be highly processed before consumption, and this has created important new marketing opportunities for bread and cereals manufacturers, as a glance at the shelves of any supermarket will confirm. The original dietary fibre hypothesis was based on epidemiological evidence, and hence on comparisons of total fibre intake amongst populations. This has led to an over-preoccupation with the absolute content of dietary fibre in foods, together with a heated and as yet unresolved debate as to how this absolute content should be defined and measured. The definition of dietary fibre used in the present paper is that of Trowell et al. (1976): 'the sum of lignin and the plant polysaccharides which are not digested by the endogenous secretions of the human gastro-intestinal tract'. It should never be forgotten that all definitions of fibre encompass a range of polysaccharides with different physico-chemical properties and biological effects. The major components of dietary fibre and their principal sources are cell wall components (cellulose, hemicellulose, lignin and pectic substances), non-structural components (gums and mucilages) and industrial additives (modified cellulose, modified pectin, commercial gums and algal poly-saccharides). Space does not permit a comprehensive discussion of the chemical and physical properties of the various materials but excellent reviews are available (for example, Selvendran er d. 1987). It is a fundamental error to assume that …