Abstract: In order to understand the effect of repeated freezing-thawing on beef quality properties and structure, vacuum packaged bovine longissimus dorsi (LD) muscle was subjected to 5 cycles of repeated freezing-thawing (one cycle was freezing －20 ℃ for 24 h and subsequent thawing under running water until the central temperature reached 0－2 ℃), and the thawing loss (TL), cooking loss (CL), water loss (WL), shear force (SF),  pH and microstructure of beef were measured after each repeated cycle. The results indicated that as the number of repeated cycle increased, beef TL and CL were significantly increased, a significant increase in beef WL was observed only after the first repeated cycle, beef SF showed a trend to significantly increase first and then decrease, pH was significantly lowered, a confused structure of muscle fiber bundles with markedly widened gaps and vacuolated structure formation in the mitochondria were observed, and the Z-disc was found to be deranged, dissolved or even diminished. In summary, repeated freezing-thawing can result in seriously damaged beef structure and obviously reduced meat quality.

Key words: repeated freezing-thawing, beef, quality properties, structure