Starch Analysis in Food

Abstract

AbstractStarch is quantitatively an important component of the human diet, being present in grains, tubers and legumes. Starch has for a long time been considered by many as being slowly but completely digested in the small intestine, resulting in modest glycemic responses and with no physiological role other than as an energy source. It is now understood that in fact the metabolic fate and physiological properties of starch can vary considerably, and both the botanical source and the effects of food processing are major determinants of starch digestibility. In addition to the nature of the starch itself, the site, rate and extent of digestion of starch in the human small intestine are influenced by a number of host factors. The rate at which starch is digested in the human small intestine results in a wide range of glycemic responses, and this physiological measurement has been used to rank foods by their glycemic index. In vitro studies have indicated that glycemic response and the rate of starch digestion are closely correlated. Rapidly digestible starch (RDS) and slowly digestible starch (SDS) fractions together represent the starch that is likely to be digested completely in the human small intestine, with any remaining starch defined as the resistant starch (RS) fraction that is available for fermentation in the large bowel. Measurements of RDS, SDS and RS can be obtained by one simple procedure. Values for the different starch fractions obtained by the in vitro method described here represent reproducible measurements that can be used to classify dietary starch according to its potential digestibility. In addition to these starch fractions, two terms, rapidly available glucose (RAG) and slowly available glucose (SAG), are introduced to reflect the rate at which glucose (from both sugars and starch) is likely to be absorbed in the small intestine.The proportions of RAG, SAG, RDS, SDS and RS in foods can be controlled by food processing. The implications of altering the rate and extent of starch digestion are potentially of great importance to public health. A full understanding of the links between dietary carbohydrates and health and the underlying mechanisms will come only from the specific measurement of individual types of dietary carbohydrates.