Acid-induced structural reorganization of fish myofibrillar protein gels: trade-off between elasticity and stability

Gel-like emulsions (GEs) stabilized by fish myofibrillar protein (FMP) were prepared, followed by post-emulsification acid treatment. Confocal laser scanning microscopy showed that free FMP aggregated and the particle size of GEs increased after acid modification. Cryo-scanning electron microscopy revealed that as pH decreased, the aggregation of FMP gradually intensified, and the structure of free FMP changed from initial regular honeycomb structure to a random lamellar structure. Rheological properties and large amplitude oscillatory shear test showed that storage modulus of acid-modified GEs significantly increased by almost 10 times (from 94 Pa to 1121 Pa), and its resistance under large strains was enhanced. Modification by pH 6 had no effect on the stability of O/W interface while pH 4 and 2 disrupted the balance of O/W interface. Acid modification inhibited the phase separation of FMP-GEs. GEs modified at pH 6 exhibited low TBARS value (0.32 ± 0.01 mg/mL) while GEs modified at pH 4 and 2 showed high TBARS value (0.58 ± 0.04 and 0.81 ± 0.03 mg/mL). Thus, acid modification may enhance the solid-like properties but compromise the stability of FMP-based GEs.