A practical approach to tailoring the texture of soy-meat hybrid batters through penetration force-guided hydration of soy protein isolates

Replicating the meat-like texture remains a major obstacle in developing next-generation meat products such as plant-meat hybrids. This study evaluated a penetration-force (PF)-guided hydration approach for four commercial soy protein isolates (SPIs; ~ 86% protein) with unique functionalities: SA (strong gel), SB (easily dispersible), SC (strong emulsification), SD (high viscosity & solubility). The PF of a lean poultry meat model formulation (control; CL) was used as a mechanical target to guide hydration optimization, under the hypothesis that optimally hydrated SPIs could replace meat at levels from 25 to 100% without compromising texture, water-binding, and structural integrity. A central composite design was employed to optimize water:soy ratios (3:1 to 5:1) and sodium chloride concentrations (0 to 3%). Stepwise (forward selection) regression modeling allowed identifying optimal conditions, which were subsequently validated. Although 100% SA and SD gels matched CL's hardness (texture profile analysis), they co-gelled synergistically with meat proteins in hybrids, resulting in significantly harder gels than the CL. In contrast, 100% SC was softer than the CL, yet SC hybrids mimicked CL's hardness at 25% and 50% replacement and consistently showed the highest final G′ (dynamic rheology), indicating superior compatibility with myofibrillar proteins. Regarding water retention, SD treatments showed the lowest cooking loss and PT₂₂ (T₂ NMR), whereas SC treatments exhibited higher loss (although closest to the CL) and larger PT₂₂ than the other SPIs. Micrographs suggested that SC formed intermediate-sized aggregates with moderate connectivity, contrasting with the larger and more highly interconnected matrices of SA and SD. Overall, the present optimization method was found to be effective for incorporating intermediate-gelling SPIs like SC into a lean model meat formulation without requiring additional structuring (e.g., extrusion). Future work should aim to refine this method for high-gelling SPIs and evaluate SC in commercial restructured products.