The effects of ultrasonic treatment on the freezing rate, physicochemical quality, and microstructure of the back muscle of grass carp (Ctenopharyngodon idella)

The application and research of power ultrasound (PU) have rarely been reported in aquatic products processing. This study evaluates the effects of PU on the freezing rate, physicochemical properties, and microstructure of the back muscle of grass carp (Ctenopharyngodon idella) at various power densities and time intervals during both marination and immersion freezing (IF). The results show that the application of PU at 0.38 W/cm2 and above during IF can significantly shorten the length of precooling stage, phase transition and, total freezing time (P < 0.05), protect muscle fiber structure, resulting in decreased thawing loss, but it exhibited no significant effect on the protein carbonyl content, total sulfhydryl content and disulfide bond content. Ultrasonic marination (UM) with a maximum power density of 0.60 W/cm2 slightly increases the protein carbonyl content and decreases the total thiols without significant effect (P > 0.05). However, the disulfide bond content increases significantly (P < 0.05) after UM at 0.48 W/cm2 and above. PU treatment at 0.38 W/cm2 and above during marination and 0.48 W/cm2 and above during IF significantly promotes lipid oxidation. UM at 0.60 W/cm2 for up to 90 min and above results in visible damage to the muscle fiber membrane of grass carp (Ctenopharyngodon idella).