Effect of calcium ions concentration on the properties and microstructures of doubly induced sorghum arabinoxylan/soy protein isolate mixed gels

Sorghum bran arabinoxylan (AX) - soy protein isolate (SPI) mixed gel with multiple network structures and greater mechanical property was previously fabricated by duo-induction of peroxidase and calcium ions. The aim of current study was to achieve continuous improvement of the properties and microstructures of this dual-induced mixed gel by regulating the calcium ion concentrations, and to clarify the influence mechanism of calcium ions. The results showed that the addition of calcium ions (≤20 mM) caused the mixed gel network to regular and smooth, and effectively enhanced the mechanical strength. With the increase of calcium ion concentration (>20 mM), the gel network structure became disordered and rough, and the springiness, adhesiveness as well as chewiness decreased significantly. Fluorescence spectra, circular dichroism (CD) and chemical interaction forces analysis indicated that for the mixed gels formed by duo-induction, the low calcium ions concentration did not only change the secondary structure and molecular conformation of the protein, but also enhance its hydrophobic interactions, hydrogen bonds and disulfide bonds, leading to the formation of filamentous protein network. However, excessive calcium ions decreased the electrostatic interactions between polysaccharide and protein networks, weakened the cross-links between the networks, resulting in the formation of granular coarse gel network and the loss of gel springiness. Overall, appropriate calcium ion concentration had a positive effect on the microstructures and texture properties of the AX-SPI mixed gels. • Calcium ions had a significant effect on the gel properties of sorghum AX-SPI mixed gel. • Appropriate Ca 2+ concentration (≤20 mM) improved the hardness and springiness of AX-SPI mixed gel. • The addition of Ca 2+ enhanced hydrophobic interactions, hydrogen bonds and disulfide bonds except electrostatic interactions. • The SPI in mixed gel formed filamentous network at low Ca 2+ ,while formed granular network at high Ca 2+ . • Low Ca 2+ could promote the improvement of strength and microstructures of mixed gel.