Effects of ultrasound-assisted tumbling on physicochemical properties, myofibrillar protein structure, and protein...

The aim of this study was to investigate the effects of ultrasound-assisted tumbling (100, 300, 500, and 700 W) with different treatment times (30, 60, 90, 120, 150, and 180 min) on the quality, myofibrillar protein structure, and protein oxidation of beef (knuckles, 48 h postmortem). Differences in physicochemical properties were assessed, including tumbling yield, protein content in the brine, cooking loss, color, texture, and moisture distribution. Additionally, protein structural and oxidative characteristics were analyzed by measuring carbonyl groups, sulfhydryl groups, and secondary structural conformations. Results indicated that ultrasound-assisted treatment increased both tumbling yield and brine protein content (P < 0.05). Compared with single tumbling (conventional tumbling without ultrasound treatment), ultrasound-assisted tumbling increased the L* value and myofibrillar fragmentation index, while reducing the a* value, hardness, and shear force (P < 0.05). Magnetic resonance imaging, low-field nuclear magnetic resonance, and cooking loss results confirmed that the ultrasound process raised the bound water content and enhanced water-holding capacity of beef (P < 0.05). Moreover, increased ultrasonic power elevated protein carbonyl content and reduced total sulfhydryl content, thus promoting protein oxidation. Conformational analyses revealed that ultrasound treatment reduced protein α-helix content while elevating β-sheet content. In summary, ultrasound-assisted tumbling improved cured beef quality by regulating water migration and modifying protein and myofibrillar structures.