The influence of refrigeration, freezing, repetitive freezing-thawing, and irradiation on meat quality were evaluated by detecting DNA damage to beef muscle tissues using the single cell gel electrophoresis assay (Comet assay). Comet tail lengths indicating DNA damage levels increased with refrigeration time up to 10 days. In the case of frozen storage, the damage was increased only for the first 15 days of storage, but after that, decreased slightly and the tail lengths at 15 days were similar to those of 3,5 days refrigerated storage. Tail lengths resulting from repetitive freezing-thawing were increased after two cycles of treatment and three cycles produced longer tails than those that had been refrigerated for10 days or kept in frozen storage for 60 days. Irradiation from 1 to 10 kGy caused the most serious DNA damage among the treatments compared in this study. The two kinds of muscle tissue were similar in the pattern of results obtained from the Comet assay.The mean tail length of the comets reflected approximately the increasing patterns of DNA damage, but the differences of values between the extents of treatment were somewhat insignificant and anomalous. Therefore, we used the concept of relative damage index (RDI) calculated from per cent cells data for each tail length range and representing a state of DNA damage. Significantly different values in RDI's made it possible to discriminate samples according to the treatment levels within each treatment.

The influence of refrigeration, freezing, repetitive freezing-thawing, and irradiation on meat quality were evaluated by detecting DNA damage to beef muscle tissues using the single cell gel electrophoresis assay (Comet assay). Comet tail lengths indicating DNA damage levels increased with refrigeration time up to 10 days. In the case of frozen storage, the damage was increased only for the first 15 days of storage, but after that, decreased slightly and the tail lengths at 15 days were similar to those of 3,5 days refrigerated storage. Tail lengths resulting from repetitive freezing-thawing were increased after two cycles of treatment and three cycles produced longer tails than those that had been refrigerated for10 days or kept in frozen storage for 60 days. Irradiation from 1 to 10 kGy caused the most serious DNA damage among the treatments compared in this study. The two kinds of muscle tissue were similar in the pattern of results obtained from the Comet assay.The mean tail length of the comets reflected approximately the increasing patterns of DNA damage, but the differences of values between the extents of treatment were somewhat insignificant and anomalous. Therefore, we used the concept of relative damage index (RDI) calculated from per cent cells data for each tail length range and representing a state of DNA damage. Significantly different values in RDI's made it possible to discriminate samples according to the treatment levels within each treatment.