Diverse mechanical properties and microstructures of sorghum bran arabinoxylans/soy protein isolate mixed gels by duo-induction of peroxidase and calcium ions

Abstract

This study investigated the molecular characteristics and rheological properties of arabinoxylans (AX) extracted from three different red sorghum brans from Shandong, Shanxi and Hebei Province in China. It was found that only the Shandong sorghum bran AX, with its high ferulic acid content and low Ara/Xyl ratio, could form a gel induced via peroxidase. Subsequently, this AX and soy protein isolate (SPI) were used to prepare the mixed gels using two crosslinking agents, namely peroxidase and calcium ions, which induced AX and SPI to form the gel networks, respectively. Dynamic rheological tests showed that the doubly induced AX-SPI mixed gel had higher storage modulus (G′) and loss modulus (G″) than mixed gel by only peroxidase or AX gel induced by one or two crosslinking agents. Moreover, Texture Profile Analysis (TPA) confirmed that the doubly induced mixed gel was harder and more elastic than the other gels. Fourier-Transform Infrared Spectroscopy (FT-IR) further confirmed that, in addition to the presence of AX intermolecular covalent cross-linked gel network by peroxidase and the connection of SPI intermolecular gel network via salt bridge (Ca2+), a partial covalent crosslinking network between AX and SPI existed in the doubly induced mixed gel. Microstructure observation of the gels revealed that the doubly induced AX-SPI mixed gel had a more regular, uniform and dense inner structure than the AX single network gel. Gels with different mechanical properties and network structures could be prepared by adjusting the order of addition of the crosslinking agents.