Effect of milk pH during heating on gelation and textural properties of heat and acid-induced milk gels

The aggregation of whey proteins and their interaction with casein micelles during milk heat treatment is influenced by the pH of milk during heating. These interactions are expected to influnce the textural properties of acid and heat-induced gels, even though all gels are formed at pH of 5.2. In this study, the influence of pre-heating milk at pH between 6.1 and 6.9 on composition, structure and texture of acid and heat–induced gels was studied. Gels produced from milk at higher pH (6.7 and 6.9) retained more moisture, had lower calcium content, and yielded higher recovery, while gels produced from milk at lower pH (6.1 and 6.35) exhibited significantly higher Young's modulus and hardness. Conversely, gels at pH 6.9 were more springy, brittle, and cohesive despite their lower firmness. Gel network formation was mainly governed by electrostatic interactions, hydrogen bridges and calcium bridges. As pH increased, enhanced electrostatic interactions and hydrogen bonding were accompanied by notable secondary structural transitions marked by decreases in α-helix and β-sheet content, increases in β-turns, and stable random coil levels—resulting in weaker protein networks. Minor pH adjustments prior to heating can profoundly affect protein aggregation, network assembly, and textural properties.