Application of bromelain-hydrolyzed Protaetia brevitarsis larvae proteins in sponge cake systems: A sustainable approach to structural and functional egg substitution

This study aimed to utilize enzymatically hydrolyzed edible insect protein as a functional egg replacer in sponge cake. Protaetia brevitarsis larvae proteins were hydrolyzed using bromelain (0–4 %) to generate samples (PBSC0–PBSC4) with tailored structural characteristics. Structural and physicochemical analyses, including SDS-PAGE, free sulfhydryl content, and surface hydrophobicity, revealed that enzymatic treatment induced protein unfolding and exposure of reactive groups. These changes enhanced foaming and emulsifying properties, as well as viscosity, contributing to improved functional performance. Degree of hydrolysis increased from 2.76 % (PBSC0) to 19.28 % (PBSC3), before declining slightly at PBSC4 (15.50 %), indicating a supra-optimal effect at high enzyme levels. When applied to sponge cake batter, the hydrolysates affected foam microstructure, flow behavior, and cohesiveness. Notably, PBSC3 demonstrated superior gas-holding capacity and batter matrix integrity during mixing and molding. The resulting cakes showed moderate physical and textural performance, with PBSC3 cakes achieving 46.50 % volume compared with 79.00 % for the egg control, and hardness values of 472.52 gf/cm² versus 210.76 gf/cm² for the control. Sensory evaluation confirmed that PBSC3 reached an overall acceptability score of 4.83/7, compared with 5.92/7 for the egg control. Although some physical attributes were inferior to the control, overall quality remained within an acceptable range for egg-free products. By linking structural modifications—such as increased sulfhydryl content and surface hydrophobicity—to functional and product-level outcomes, this study provides a structure–function framework for insect protein applications and highlights their potential in sustainable bakery systems.