Effect of High Amylose Corn Starch on the Structure, Cooking Quality and Starch Digestibility of Extruded Buckwheat Noodles

The effects of addition of different amounts (10%, 20%, 25% and 30%) of high amylose corn starch (m/m, based on buckwheat flour) on the structure, cooking quality and digestive characteristics of extruded buckwheat noodles were explored. The results showed that the diameter and gelatinization degree of extruded noodles decreased with increasing addition of high amylose corn starch. The X-ray diffraction results showed that noodles with added high amylose corn starch exhibited the typical B-type peaks of amylose not completely gelatinized in addition to V-type crystallization peaks. Thermodynamic properties also indicated partial gelatinization of amylose. After addition of high amylose corn starch, the color of noodles became lighter and brighter, the optimal cooking time was shortened, and the cooking loss percentage increased from 9.90% to 12.43%. When the addition of high amylose corn starch was 25%, the noodles began to break. The hardness of noodles increased from 2105.709 to 3680.401 g, and the elasticity decreased from 0.961 to 0.866. The results of scanning electron microscopy (SEM) showed that with increasing amount of added high amylose corn starch, cracks appeared in the dense structure of noodles gradually, and more starch grains were not completely gelatinized in the crosssection of noodles. In vitro starch digestion experiments showed that with increasing addition of high amylose corn starch, the rate of starch hydrolysis and predicted glycemic index (pGI) decreased, and resistant starch (RS) content increased. The pGI of extruded buckwheat noodles decreased from 74.28 to 66.31 and RS content increased from 34.43% to 47.86% after addition of 30% high amylose corn starch.