Abstract: The objective of the present study was to explore the relationship of protein oxidation, muscle structural changes and jumbo squid mantle quality during ultrasound-assisted thawing. Frozen jumbo squid mantles were thawed by ultrasonic treatment using different power gradients (100, 300, and 500 W) at different temperatures (5 and 10 ℃). The U5-5 treatment (5 ℃, 500 W) caused the smallest thawing and cooking loss. Low-field nuclear magnetic resonance (LF-NMR) suggested that U5-5 could reduce juice loss. The seven different thawing methods showed significant differences in carbonyl content, total sulfhydryl content, dityrosine content and surface hydrophobicity (P < 0.05). U5-3 (5 ℃, 300 W) and U5-5 had little effect on the carbonyl content of myofibrillar protein. U5-3 caused the highest total sulfhydryl content and the smallest dityrosine content, while refrigerator thawing and U5-1 (5 ℃, 100 W) caused the least exposure of hydrophobic groups on the protein surface. Raman spectroscopy showed that ultrasonic-assisted thawing could retard the conversion of α-helices to β-sheets, β-turns and random coils. These results demonstrate that ultrasonic-assisted thawing at 5 ℃ (U5-3 and U5-5) can improve product quality and defer protein oxidation.

Key words: ultrasonic-assisted thawing; jumbo squid; protein oxidation; quality; structural transformation