This study investigated the effects of different combinations of sous-vide cooking temperature (11, 14 and 17 h) and time (57, 60 and 63 ℃ ) on the eating quality of beef Semimembranous muscle in terms of pH value, internal color of cooked meat, cooking loss, tenderness, and sensory scores. The results showed that as cooking time and cooking temperature increased, the pH value, shear force, cooking loss, L* value, and H* value of bovine Semimembranous muscle all showed an increasing trend, while the a*, b*, C*, and overall sensory score significantly decreased. The cooking loss increased from 28.98% to 33.06% over 11 to 17 hours, and from 27.2% to 36.5% over 57 to 63 ℃ ; the shear force increased from 40.14 to 61.08 N over 57 to 63 ℃ , indicating that as the cooking strength increased, both the water-holding capacity and tenderness decreased. At 57 ℃ and 11 hours, cooked beef had the lowest shear force of 42.58 N, which meets the demand of Chinese consumers for “tender meat”, and the highest scores for overall acceptability and internal color. Therefore, cooking at 57 ℃ for 11 hours can effectively improve the tenderness and water-holding capacity of beef Semimembranous muscles while avoiding some problems such as the reddish color and bland flavor of cooked meat and imparting it with better sensory quality and higher yield.

The quality differences and Raman spectroscopic features of beef, which was frozen for 0–11 months followed by being thawed and displayed for 0–21 days were investigated. Frozen storage did not significantly affect the color blooming ability, in which minimal change in the color parameter redness and yellowness values of thawed beef in the later stage of frozen storage occurred. As such, it was not able to distinguish between frozen-thawed and non-frozen-thawed meat directly in terms of color changes. The total viable count and the total volatile basic nitrogen content increased sharply in the frozen-thawed meat subjected to 11-month frozen storage. The thiobarbituric acid reactive substances value increased dramatically from 0.18 to 0.29 mg/kg during 11-month frozen storage. Raman spectroscopy data showed that the stability of the protein secondary structure of thawed beef became worse after 3 months of frozen storage, of which the relative content of α-helix and β-sheet decreased significantly to 21.46% and 28.94% during 11-month frozen storage, respectively. The findings suggest that quality deterioration occurred for the frozen-thawed beef, and Raman spectroscopy could be a potential method to distinguish unfrozen meat from frozen-thawed meat.

To explore the oxidation mechanism of wooden breast myofibrillar protein (WBMP), oxidative breast MP (OBMP) was obtained from different doses (3, 10, and 20 mmol/L) of H₂O₂ oxidized normal breast MP (NBMP). The results showed that the Zeta-potential, particle size, solubility, sulfhydryl, and carbonyl contents of OBMP-3 (3 mmol/L, low-dose free radicals) and WBMP were similar. Fluorescence spectrum analysis showed that the oxidation of low-dose free radicals led to a significant increase in the surface hydrophobicity (from 214.03 ± 10.03 to 393.50 ± 10.33) and tryptophan fluorescence intensity (from 185.71 to 568.32). In addition, the α-helix content of WBMP decreased significantly from (37.46 ± 1.15)% (NBMP) to (34.70 ± 2.04)%, while β-sheet and random coil contents increased significantly (P < 0.05) from (14.37 ± 0.69)% and (22.24 ± 0.78)% (NBMP) to (17.70 ± 0.87)% and (25.20 ± 1.47)% (WBMP). In summary, low-dose free radical oxidation attacks protein groups, inducing secondary and tertiary structural changes, leading to the formation of WBMP. This work will provide a theoretical basis at the molecular level for exploring the mechanism of functional degradation of WBMP.

In order to explore the effect of pH on the structure and thermal stability of myoglobin, the molecular structure and surface hydrophobicity of myoglobin at normal pH (5.6) and high pH (6.4) under refrigerated (4 ℃) and heating (72 ℃) conditions as well as its thermal denaturation degree were characterized by various spectroscopic techniques. The results showed that pH had no significant effect on the conformation of myoglobin at 4 ℃. However, the endogenous fluorescence intensity, protein surface hydrophobicity and thermal denaturation of myoglobin at 72 ℃ were significantly higher at pH 5.6 than at pH 6.4. The tertiary structure of myoglobin was more severely destroyed at pH 5.6 than pH 6.4, resulting in reduced thermal stability. Therefore, environmental pH can affect the thermal stability of myoglobin by altering its structural stability. High pH can increase the thermal stability of myoglobin, which is an important cause for the persistent pink color of dark, firm, dry (DFD) beef during cooking.