Effect of Frozen Storage Time on the Color and Oxidative Stability of Lamb Rolls

Fresh lamb rolls were selected for frozen storage for up to 6 months, with regular sampling at 1-month intervals. The trend in the color of lamb rolls during the storage period was systematically analyzed, and their changing patterns were comprehensively evaluated by measuring the degree of fat oxidation and the oxidative degradation of proteins. The results showed that as the storage time increased, the color of lamb rolls changed significantly, mainly manifested by a decrease in the brightness and redness values, and an increase in the yellowness value. This change began to appear in the second month of storage and leveled off in the fifth month. During frozen storage, the relative content of oxymyoglobin declined markedly (P < 0.05), whereas the relative content of metmyoglobin showed an opposite trend (P < 0.05), which was closely related to the color change of lamb rolls from bright red to dark brown. After 6 months, the total sulfhydryl content decreased by 65.9%, the relative content of metmyoglobin increased to 27.1%, and the carbonyl content and thiobarbituric acid reactive substances (TBARS) value increased by 2.15 times and 30.6%, respectively. In addition, fluorescence and ultraviolet spectroscopy showed that myoglobin heme iron porphyrin structure was damaged, and hemoprotein was oxidized and degraded. The secondary structure of myoglobin changed with frozen storage time, the relative content of α-helix decreased, while the relative contents of β-sheet and β-turn increased. This further confirmed that myoglobin was oxidized and degraded, which in turn affected the color stability of lamb rolls during storage.