Abstract: The present study aimed to investigate the effect of fat contents on myofibrillar protein (MP) oxidation, physicochemical characteristics and sensory properties of beef patties during repeated freeze-thaw cycles, and to elucidate the correlation of freeze-thaw treatment and lipid content with protein oxidation. Round beef patties ((100 ± 2) g per piece) with different fat contents were manufactured by adding 0% (F0), 10% (F10), and 20% (F20) beef tallow and the same proportions of salt and other accessory materials to ground beef loin and then stored at -18 ℃ and one-week frozen storage followed by thawing under running water to a core temperature of 0–2 ℃ were carried out five times during the process. The color parameters (a*, b* and L*) and thawing loss rate were determined and MP was extracted from the patties for the measurement of carbonyl content, total sulfhydryl content and protein solubility after each freeze-thaw cycle. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to evaluate MP aggregation and degradation. The results indicated that a* value, total sulfhydryl content and protein solubility decreased significantly, while b* and L* values, thawing loss and carbonyl content increased with increasing number of freeze-thaw cycles and increasing fat addition. SDS-PAGE analysis showed that myosin heavy chains (MHC) were aggregated and paramyosin and actin were degraded with increasing number of freeze-thaw cycles and increasing fat addition. The sensory quality of beef patties increased with the increase in fat content, but decreased with increasing number of freeze-thaw cycles, especially after three freeze-thawing cycles. In addition, harder texture and increased juice loss were observed. Correlation analysis showed that color parameters (L*, a* and b*), thawing loss and protein oxidation indexes (carbonyl content, total sulfhydryl content, protein solubility) were significantly correlated with freeze-thaw cycles and fat content (P < 0.05 or P < 0.01). The results proved that freeze-thaw cycles could induce protein oxidation in beef patties and quality deterioration. Increased fat content enhanced sensory scores, but accelerated protein oxidation and affected physicochemical properties of beef patties. In practice, proper fat content and constant low temperature are necessary for better quality of beef products.

Key words: beef patty, freeze-thaw cycle, fat content, myofibrillar protein, oxidation, quality