Effect Of Extrusion Cooking Research Articles

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

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.

Protein nutritional value of extrusion-cooked wheat flours

The effect of extrusion cooking on the protein nutritional value of wheat flour and whole-grain wheat flour was studied. Amino acid analysis showed lysine retention between 63 and 100%. The retention was positively affected by an increase in feed rate, and negatively by an increase in screw speed. The prominent lysine damage under severe conditions was probably due to formation of reducing carbohydrates through hydrolysis of starch. The loss of other amino acids was small. The BV of extruded wheat flours was significantly reduced in the products showing the most prominent lysine loss. However, no effect was seen in TD. In contrast, a decrease in BV of extruded whole-grain flour was accompanied by a significant reduction in TD. Extrusion cooking of wheat starch did not affect the nitrogen balance in rats given casein/starch diets containing raw or extruded starch.