Effects of soy protein isolate hydrolysate on the structural and functional properties of yam starch during extrusion

This study investigated the interaction between yam starch (YS) and soy protein isolate hydrolysate (SPH), and their effects on in vitro digestibility of starch through extrusion treatment. Results indicated that SPH with 6 % hydrolysis degree had the lowest relative molecular mass. X-ray diffraction and Raman spectroscopy revealed an increase in the relative crystallinity of extruded yam starch (EYS) from 17.45 % to 22.45 % and a decrease in the half-peak width at 480 cm^-1. Its short-range ordering improved with increased SPH addition. Differential scanning calorimetry results demonstrated that SPH enhanced the thermal properties of EYS. Additionally, the solubility, peak viscosity, and setback viscosity of EYS decreased with an increase in the SPH content. Particle size analysis revealed that SPH addition decreased the particle size of EYS. Scanning electron microscopy and confocal laser scanning microscopy showed that the surface of EYS roughened and SPH molecules attached to the surface. In vitro digestion results indicated that SPH hindered the contact between EYS molecules and digestive enzymes and increased the resistant starch content of EYS from 8.31 % to 23.39 %. This study presents a new method for modification of starch using protein hydrolysates during extrusion.