Calcium-mediated percolation and droplet-reinforced composite structuring of yeast protein isolate in acid-stable...

Yeast protein isolate (YPI) is a promising sustainable protein source. However, its structural functionality is limited under acidic conditions, restricting its application in semi-solid emulsion systems. In this study, we engineered an acid-stable YPI-based network by integrating with low-methoxyl pectin (LMP) with calcium-mediated ionic crosslinking. A critical gelation threshold was identified at 60 mM Ca²⁺, above which calcium-induced junction zones established a continuous load-bearing scaffold at pH 3.0, consistent with a percolation-type transition. Incorporation of dispersed oil droplets (10-40%, w/w) transformed the system into a reinforced composite gel in which YPI-coated droplets functioned as mechanically integrated domains. Increasing oil fraction enhanced storage modulus and yield stress, revealing a transition from matrix-dominant elasticity to filler-reinforced mechanical behavior. At intermediate oil fractions (20-25%), cooperative interactions between ionic crosslinks and droplet-mediated stress transfer produced acid-stable emulsion gels with viscoelastic and textural properties comparable to conventional high-fat mayonnaise despite reduced oil content. Dynamic rheological and creep-recovery analyses indicated that network mechanics were governed predominantly by reversible ionic interactions, enabling structural attenuation under shear and rapid reconstruction upon rest. Freeze-thaw evaluation further demonstrated effective water confinement and droplet immobilization within the crosslinked scaffold. These findings establish a calcium-driven composite structuring strategy for enhancing the functional performance of yeast-derived proteins in acid-stable emulsion gel systems.