Effects and action mechanisms of polygonatum sibiricum polysaccharide on gel properties of soybean protein isolate

In this study, the polygonatum sibiricum polysaccharide (PSP) was extracted using the deep eutectic solvent (DES) and added into soybean protein isolate (SPI) to prepare the SPI - PSP gel. Afterwards, the SPI - PSP gel properties were analyzed to explore how the PSP affected the gel properties and the gelation mechanism. When the PSP addition was from 0% to 2.5% (w/v, g/100 mL), the gel hardness increased from (18.70 ± 2.10) g to (36.10 ± 3.22) g. The gel consistency was enhanced, but the gel flow behavior was inhibited. Besides, the gel water-holding capacity rose from (83.56 ± 1.13) % to (89.80 ± 1.28) %, and the gel thermal stability was enhanced due to the PSP addition. The free sulfhydryl group, the protein structure changes and the intermolecular forces in the SPI - PSP gels were evaluated for exploring the gel formation mechanisms. It was found that the free sulfhydryl group content increased from (2.77 ± 0.01) to (3.40 ± 0.00) μmol/100 mg. The PSP significantly diminished α-helix and β-turn contents and elevated β-sheet content of the SPI secondary structure. So, more hydrogen bonding was formed to improve the SPI - PSP gel formation due to the changes of the SPI secondary structure. It was provided a basic to adjusting the gel properties according the polysaccharide addition.