TECHNOLOGICAL TREATMENTS OF CEREALS - REPERCUSSIONS ON THE PHYSIOLOGICAL-PROPERTIES OF STARCH

The structural and physicochemical properties of starches in cereal food vary continuously according to the starch characteristics (botanical origin, amylopectin/amylose ratio, etc.), the food water content, the temperature and the other food components (fibres, proteins, lipids, etc.). The starch characteristics, digestibility (rate of available starch fraction) and thus nutritional properties (transit time, food glycaemic and insulinaemic indexes) can be modified by industrial hydrothermic processing (i.e. panification, pastification. extrusion cooking etc.). In cereal products, one fraction - the 'resistant starch' (RS) fraction - is not digestible, whether in vitro or in vivo. Four different RS fractions have been identified in the cereal products, they are the native starch, the retrograded amylose, the amylo-lipid complex and the encapsulated gelatinized starch. The amount and quality of the RS fractions in cereal food can be modulated by industrial processing. After reaching the large intestine, the RS fractions are fermented by the colonic flora, resulting in short chain fatty acids (SCFA). In SCFA, the RS profiles, compared to that of the conventional fibres, are lower in acetate and higher in butyrate. The SCFAs are an energetic fuel to the colonic cells (butyrate) and to the body as a whole (acetate and propionate). Further studies on human nutrition are needed to appreciate the nutritional consequences (insulin sensitivity and glucose tolerance, lipid metabolisms and impact of colonic,cell) of industrial processing and its impact on starch availability.