Modification of functional, rheological and structural characteristics of myofibrillar proteins by high-intensity ultrasonic and papain treatment

The effects of sonication duration (15 and 30 min) and papain enzyme treatments on the conformational, physicochemical and functional traits of myofibrillar proteins (MPs) were addressed in this study. As the ultrasound duration was increased, the water holding capacity (WHC), solubility, foaming and emulsifying properties were improved as a result of the changes in the particles size distribution and zeta potential. Our results indicated that the turbulence force caused increments in the surface hydrophobicity and significant changes in the secondary structure. Also, the rheological properties were influenced by both cavitation force and papain treatment. According to the observations, the samples treated with sonication (for 15 and 30 min) and enzyme were more elastic with higher viscosity, as compared to the control. Compared with the control, enzymolyzed samples indicated better functionality. Moreover, papain treatment led to the increase of the hydrophobicity groups on the surface of proteins and the decrease of the amount of alpha-helix and beta-sheet structures. It was noteworthy that the most changes in the structure and techno-functionality of myofibrillar proteins were observed for the sample affected by the simultaneous application of papain treatment and 15 min sonication. The highest values in the surface hydrophobicity, specific surface area, net charge, storage modulus, solubility and WHC belonged to this sample. However, enzyme-modified samples exposed to the longer sonication time (30 min) demonstrated reductions in solubility, WHC and surface hydrophobicity, as well as increases in the particle size distribution and protein turbidity.