pH and temperature-dependent gelation of Torreya grandis nut protein: Molecular interactions and gel network...

Understanding the gelation behavior of novel plant protein under varying pH and temperature conditions is crucial for designing food systems with tailored texture, stability, and functional properties. In this study, we investigated the effects of pH and temperature on the aggregation behavior and heat-induced gelation of TGNP. The results showed that TGNP gelation was strongly influenced by both pH and heating temperature. Near the isoelectric point (pH 4), the protein exhibited minimal solubility (8%) and large particle size (>3000 nm) due to extensive aggregation, conditions that were unfavorable for the formation of a well-developed gel network. In contrast, strongly acidic (pH 2), neutral (pH 7), and alkaline (pH 10) conditions improved protein solubility (62%, 81% and 89%, respectively) and reduced particle sizes (400-900 nm), promoting better molecular dispersion and facilitating heat-induced gelation. Alkaline conditions particularly enhanced protein unfolding, exposing buried hydrophobic residues and sulfhydryl groups, which promoted hydrophobic interactions and disulfide cross-linking. These interactions resulted in the formation of the strongest and most stable heat-induced gels. Rheological analysis further revealed that stable elastic gels with higher viscosity, gel strength, and water-holding capacity were predominantly formed at neutral and alkaline pH, especially after heating at 95 °C. Disulfide bonds and hydrophobic interactions were identified as the primary forces governing TGNP gel network formation, although their relative contributions varied with pH and temperature. Overall, these findings provide new insights into the gelation mechanism of TGNP and highlight its potential as a novel functional protein ingredient for food systems requiring low gelation concentrations.