Effects of processing on availability of starch for digestion in vitro and in vivo; I Extrusion cooking of wheat flours and starch

Abstract

The effect of extrusion cooking on availability of starch for digestion in wheat products was tested in vitro and in vivo . Hydrolysis in vitro was measured using salivary amylase and the in vivo availability was evaluated by measuring the plasma levels of glucose and insulin after a gastric load in conscious rats. Ther fermentability of starch in human dental plaque in situ was also studied. Extrusion cooking of white flour and whole-grain wheat flour rendered the starch more susceptible to salivary α-amylase than did boiling for 20 min in water. Consequently, the pH drop in dental plaque was more pronounced with extruded materials. The rate of starch absorption in vivo , as judged from the plasma glucose pattern, was similar for boiled samples and for samples extruded under mild conditions. However, under more severe extrusion conditions, there was a significant increase in plasma glucose response. In the case of white flour, this enhanced glucose response was accompanied by an increased insulin response. Thus, processing conditions can influence both the glycaemic response to starch and its cariogenic properties.