Freeze-thaw stability of oat protein isolate gels: Effect of pH and gelation methods

To elucidate the relationships among pH, gelation mechanisms, and freeze-thaw stability, a comparative study was conducted on heat- and transglutaminase (TGase)-induced oat protein isolate gels over a pH range of 5.0–9.0. Freeze-thaw cycles induced structural deterioration, evidenced by enlarged pores and increased hardness. The results demonstrated that pH strongly affects protein structural organization. As pH increased, gels visually transitioned from opaque, white, granular forms to more translucent, brown, chain-like structures. SEM and CLSM observations revealed progressive microstructural changes, with network density increasing substantially at higher pH values. Comparative analysis indicated that gels formed at pH 8.0–9.0 exhibited superior molecular characteristics, including increased surface hydrophobicity (H₀), enhanced disulfide bond formation, more ordered secondary structures, and more stable tertiary conformations, relative to gels formed at pH 5.0–7.0. Heat-induced gels displayed maximal freeze-thaw stability at pH 8.0, whereas TGase-induced gels remained stable at both pH 8.0 and 9.0. These findings underscore the superior freeze-thaw resistance of TGase-induced gels and highlight the synergistic effects of pH regulation and gelation methods on improving oat protein isolate gel stability, providing a scientific basis for optimizing the freeze-thaw performance of oat protein isolate -based functional foods.