Physical properties and chemical forces of extruded corn starch fortified with soy protein isolate

Abstract

SummaryThe effect of soy protein addition on physical properties of extruded corn starch was studied. The correlations between the chemical bonds in proteins and the physical properties of extrudates were analysed. Increasing soy protein isolate content resulted in higher expansion ratio (ER) but lower bulk density (BD), hardness, water solubility index (WSI), degree of starch gelatinisation (DSG), content of sulphydryl (SH) groups and protein solubility in phosphate buffer. In the other hand, increasing the processing temperature resulted in higher ER, water absorption index, DSG, contents of the SH group and disulphide (SS) bond but in lower specific mechanical energy, BD, hardness and WSI. The results indicated that changes in the chemical bonds in proteins had a significant effect on the apparent physical properties of extrudates. More protein–protein and protein–starch cross‐linking reactions occurred through new chemical linkages, such as the nondisulphide covalent bonds and hydrogen bonds, which are beneficial to the expansion of starch‐based products.