A study on the structure and gel properties: construction of co-assembed structures of rice globulin and soybean protein based on pH cycling technology

Abstract

Soybean protein natural gel products present certain challenges, including poor stability and inadequate mechanical strength, which constrain their application and advancement in the field of gel products. Rice globulin can compensate for these limitations. Three co-assembled structures were constructed by pH cycling: rice globulin-soybean 11S protein (RG-11S), rice globulin-soybean 7S protein (RG-7S) and rice globulin-soybean protein (RG-SP). Both fluorescence and ultraviolet-visible absorption spectroscopy confirmed that the microenvironment of aromatic amino acid residues was changed, and the polarity was enhanced after adding rice globulin. When the ratio of compound proteins was 1:10, the β-turns content in RG-11S increased by 18.3 %. The α-helixes content in RG-7S and RG-SP increased by 10.45 % and 11.51 %, respectively, the particle size was also at its minimum. Scanning electron microscopy revealed that RG-11S forms irregular, smooth lamellar structures, RG-7S forms a porous, mesh-like structure, and RG-SP forms a stacked, layered structure. Meanwhile, an analysis of the texture properties of the gel samples was conducted. The results indicated that the RG-7S composite protein gel exhibited the highest springiness (0.76 mm) and chewiness (47.67 g), while the RG-SP composite protein gel demonstrated the highest gumminess (46.33 g) at this ratio. Furthermore, rheological experiments confirmed that the gel quality was optimal when the ratio of compound protein was 1:10. This research has deepened our understanding of how plant protein molecules interact. Key practical issues relating to the use of soybean protein have been resolved, paving the way for the rational design of composite protein gels.