Study on the mechanism of change in fracture strength of high moisture plant textured protein fibers

In order to investigate the mechanism of changes in the breaking strength of high-moisture textured vegetable protein (HMTVP) fibers, HMTVP was prepared in this study by a twin-screw extruder using different starch additions and screw speeds. The key factors affecting the fiber strength were revealed by analyzing the changes in the microstructure, chemical bonding, intermolecular forces, and the secondary structure of proteins in HMTVP. The results showed that the fiber strength of HMTVP showed a tendency of decreasing and then increasing with the increase of starch addition and screw speed, with the minimum values of 0.70 N (7.5%) and 0.73 N (280 r·min^-1), respectively. The changes of free sulfhydryl and disulfide bond contents were closely related to the fiber strength. With the increase of screw speed and starch content, the percentage of β-folding of HMTVP increased by more than 12%, while the percentage of β-turning angle decreased by about 19%, indicating that the molecular structure of the protein was transformed from disorder to order. The relationship model between intermolecular forces or chemical bonds and the fiber strength of HMTVP was established by logistic function fitting. It provides theoretical support for the precise regulation of the process of starch addition and screw speed, and provides a theoretical basis for the development of HMTVP products with meat-like fiber strength.