Conformational changes and product quality of high-moisture extrudates produced from soy, rice, and pea proteins

This study aimed to investigate the performance of soy, pea, and rice proteins during high-moisture extrusion (HME) to understand better how the plant proteins transform into a fibrous structure. It found that rice protein isolate formed weak structures with the fewest layers and fibrous structures. Extruded pea protein concentrate produced more obviously layered structures than extruded soy and rice samples. Extruded soy protein isolate showed a compact gel structure, whereas extruded soy protein concentrate showed a thin fibrous structure. Meanwhile, the chewiness of soy and pea protein extrudates surpassed that of rice protein extrudates by approximately 10 N. After undergoing HME processing, there was a marked 5-10% decrease in extracted proteins (p < 0.05) in solvents with urea, dithiothreitol, and sodium dodecyl sulphate, when comparing the soy and pea extrudates with their raw materials, except for the extruded rice protein isolate (ERPI) with rice protein isolate. It could be deduced that HME processing promoted the formation of aggregates in soy and pea proteins that the extracted solvents could not dissolve. It also revealed that HME induced an increase in the content of S-S bonds in extruded soy and pea protein but a decrease in ERPI. The percentage of random coils in commercial pea protein, initially at 14.04%, saw a significant increase to 19.36% after extrusion (p < 0.05), indicating that pea protein is more likely to form intermolecular hydrogen bonds. In this study, the secondary structures of rice and soy protein did not show significant changes after extrusion.