Effects of initial freezing rate on the changes in quality, myofibrillar protein characteristics and myowater status of beef steak during subsequent frozen storage

This study aimed to address the effects of initial freezing rate on quality change, myofibrillar protein denaturation and water status evolution of beef muscles during subsequent frozen storage (0, 7, 30, 60, 90 and 180 d). Beef steaks were allocated to different freezing methods, including -80/-18 °C (frozen at -80 °C for 7 d and then stored at -18 °C until the end of duration), -80/-12 °C (frozen at -80 °C and then stored at -12 °C), -18 °C (frozen and stored at -18 °C) and -12 °C (frozen and stored at -12 °C). Results showed a rising degree of quality deterioration, myofibrillar protein denaturation and water migration with extended storage duration, wherein significant impacts were observed by the initial freezing rate. Samples subjected to -80/-12 °C treatment exhibited significantly lower (P < 0.05) thaw loss, cook loss, shear force value and colour difference coefficient ΔE than those in samples of group -12 °C. Similar results were observed between -80/-18 °C and -18 °C groups. Besides, initial quick freezing samples exhibited less severe protein denaturation (higher solubility, total sulfhydryl content and lower surface hydrophobicity), reduced water mobility (lower T2 relaxation times) as well as relatively compact ultrastructure of muscle. Noteworthily, no tangible differences were found in the quality attributes between beef samples subjected to -18 °C and -80/-12 °C throughout frozen storage (P > 0.05).