Design and characterization of soy protein isolate‐chitosan‐dietary fiber ternary composite gels: effects on water holding capacity, texture and structure

Abstract BACKGROUND Rational design of composite gels demands innovative strategies to enhance structural and functional properties. Dietary fibers (DFs) offer promising potential for reinforcing protein–polysaccharide networks, but their role in soy protein isolate (SPI)‐chitosan (CS) binary systems is underexplored. RESULTS A novel ternary composite gel from SPI, CS and DF was developed to investigate DF‐mediated reinforcement mechanisms. The synergistic combination of microbial transglutaminase (MTGase) cross‐linking and heat treatment significantly enhanced the water holding capacity (WHC) of SPI‐CS‐DF, achieving the highest 30.32% increase compared to single treatments. SPI‐CS with 1 mg mL −1 citrus dietary fiber (CDF) under the combined treatment exhibited the highest WHC (40.82% increase versus SPI‐CS). Furthermore, texture analysis revealed that the addition of 5 mg mL −1 apple dietary fiber (ADF) and 5 mg mL −1 CDF increased gel strength by 37.31% and 36.27%, respectively. However, the addition of oat dietary fiber (ODF) simultaneously reduced the gel strength and hardness. Fourier transform infrared spectroscopy, scanning electron microscopy and confocal laser scanning microscopy demonstrated that ADF and CDF promoted uniform protein networks with porous structures, whereas ODF disrupted matrix continuity. MTGase‐treated gels showed higher amide I peak intensity, which exhibited stronger covalent cross‐linking. CONCLUSION Overall, DF type and concentration are critical to tailoring SPI‐CS gel structure and performance. MTGase‐heat treatment combined with appropriate DF addition offers an effective strategy to improve WHC and mechanical properties in composite gels. These results provide a theoretical foundation for designing high‐performance gel systems with potential applications. © 2026 Society of Chemical Industry.