Acid-induced Gels from Mixtures of Micellar Casein and Pea Protein: Effect of Protein Ratio and Preheating Route

Enhancing the sustainability of dairy products through the partial substitution of dairy proteins with plant proteins requires exploring formulation and processing strategies. This study investigates the gluconic-δ-lactone (GDL)-induced hybrid gels from commercial micellar casein isolate (M) and pea protein isolate (P) dispersions (5% w/w protein content). Variations in the M/P ratios (3:1, 2:2, and 1:3) and preheating routes (Route 1: preheating M and P dispersions together; Route 2: preheating them separately) impacted the physical/conformational properties of protein dispersions as well as the rheological/structural features of resulting gels. Small and large amplitude oscillatory shear (SAOS and LAOS) tests revealed that lower M/P ratio led to earlier gelling points and increased the stiffness and elasticity of hybrid gels in the linear viscoelastic (LVE) region. All gels transitioned from elastic to plastic behavior in the non-linear viscoelastic (NLVE) region, with lower M/P ratio showing reduced stretchability and faster structural breakdown. Regardless of routes, the preheating step (95 °C, 30 min) disintegrated inherent aggregates/agglomerates in these commercial protein ingredients, leading to smaller particle size, but higher protein solubility, surface hydrophobicity, and |ζ-potential|. Pea proteins formed soluble aggregates during preheating, but the presence of micellar caseins (Route 1) hindered this process. Consequently, mixtures with lower M/P ratio and from preheating route 2, possessed higher quantities of pea protein soluble aggregates, forming a compact gel network with low water mobility, as observed by CLSM, STED, and LF-NMR. These findings show the potential for using pea proteins in acid-induced gel foods like yogurt and paneer-type cheeses.