Effect of pH on the structural properties and emulsification of myofibrillar proteins of large yellow croaker (Larimichthys crocea)

Properties of myofibrillar proteins (MPs) in Larimichthys crocea remain to be further studied to meet the high-value development and utilization of MPs. The purpose of this study is to investigate the effect of different pH on the structural and emulsifying properties of myofibrillar protein in L. crocea. MP from L. crocea was treated with low-salt phosphate buffer at pH 2, 4, 6, 8, 10 and 12, and MP degradation was analyzed by SDS-PAGE. Moreover, the hydrophilicity of MP was investigated by contact angle and fluorescence spectrophotometry. Emulsions were prepared with MP solution at different pH and soybean oil at ratio of 1∶1 (V/V) by high-speed homogenization. The stability of emulsions was determined by analyzing the droplet potential, particle size and the emulsion index of emulsions. At pH 4, the band color of MP in SDS-PAGE was light. At pH 6-12, the myosin heavy chain band largely disappeared; however, the actin band gradually deepened in color and macromolecular aggregates appeared at the top of band. The comprehensive analysis of contact angle and fluorescence spectrum showed that the hydrophobicity of MP increased with pH. Meanwhile, the MP emulsions were negatively charged with the Zeta potential absolute value of (49.63±1.52) mV and small emulsion droplets at pH 8, exhibiting better stability than MP emulsions at other pH values. However, the MP emulsions showed poor emulsion stability and even demulsification occurred at pH 12. The change of MP structure was beneficial to improve the stability of MP emulsions at pH 8. These results can provide a theoretical basis for the development and application of MP from L. crocea in the food industry.