Acid-Induced Gelation of European Eel Protein Isolate Fortified with Fish Oil: Enhancement of Physicochemical, Microstructural and Thermal Properties

Aims: This study aimed to explore the gelling capacity of European eel protein isolate (EPI) through the formulation of novel emulsion protein isolate-based gel (EPIGs) and to evaluate how fortification with bioactive European eel oil (EO) could influence the structural and functional properties of acid-induced gels.

Methods: EPIGs were prepared by heat treatment (90°C/60 min) of EPI dissolved in acetic acid (20%, v/v). followed by emulsification with EO at two distinct ratios: 1:2 and 1:4 (EO: EPI, w/w). The resulting gels were characterized using Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), texture analysis, and scanning electron microscopy (SEM).

Results: A 4% EPI solution in acetic acid formed a gel at 54°C, indicating superior thermal stability and approving strong gelling potential. FTIR analysis confirmed the successful incorporation of EO into the gel matrix, while TGA revealed a slight increase in thermal degradation onset temperatures with higher EO content (from 375°C for EPIG1:4 to 382°C for EPIG1:2). Texture analysis showed that EO incorporation slightly enhanced gel elasticity (from 12.93 mm to 13.19 mm), attributed to interactions between oil droplets and the protein matrix. SEM microstructural evaluation indicated that higher EO amount (EPIG1:2) resulted in larger pore formation, whereas EPIG1:4 exhibited a more compact, less porous structure.