Thermal-induced tapioca starch/yeast protein composite gels for texture-modified food design: effect of component ratio on gel strength, viscoelasticity and microstructure of protein-filled starch network.

To develop soft gel matrices for texture-modified food applications, this study examined how varying the tapioca starch/yeast protein (TS/YP) mass ratio (100:0 to 70:30) influences the texture of composite gels and the underlying mechanisms. Results showed that as the YP proportion increased, water retention decreased, as reflected by a reduction in water-holding capacity from 99.22% to 89.33%, which was attributed to the weaker water-binding capacity of YP relative to TS. Gel strength and breaking force peaked in the 95%TS/5%YP gel, beyond which they decreased due to an impaired gel network integrity. Rheological analysis revealed that all systems presented shear-thinning behavior, with 95%TS/5%YP showing the highest G' and G″, while excessive YP (10%-30%) reduced both moduli. Multi-level analyses revealed that YP regulates gel texture through a balance between its filling effect and steric hindrance, coupled with competitive water absorption. SEM imaging indicated a denser microstructure in the 95%TS/5%YP gel, suggesting that moderate YP incorporation contributed to gel network reinforcement. In contrast, higher YP levels promoted phase separation, enlarged pores, and weakened the gel network by disrupting cross-linking between starch chains. These structural changes aligned with altered starch behavior: increasing YP lowered pasting viscosity and gelatinization enthalpy, indicating suppressed starch hydration and granule swelling. FTIR analysis suggested changes in hydrogen bonding and structural order, possibly associated with inhibited amylose leaching caused by water competition between YP and TS. These findings provide a physicochemical basis for the development of texture-modified foods while promoting the valorization of yeast protein by-products.