BACKGROUND AND ABJECTIVEThe aims of our research were to evaluate the effects of low doses of gamma irradiation (۳-۷ kGy) and chitosan coating on microbial quality including total bacterial populations and pathogens in ground beef.MATERIALS AND METHODSFresh raw ground beef samples included non-irradiated, coated with ۲% chitosan (Ch-coated), irradiated (Cobalt-۶۰ gamma-ray source), and finally ch-coated and irradiated samples (Ch-۳-۷ kGy). All samples were analyzed periodically.RESULTS AND DISCUSSIONThe initial TVC (Day ۰) of controls (non-irradiated) was ۵.۹ log cfu/g which reduced to ۴.۲, ۵.۱ and ۳ respectively at the dose of ۳ kGy, ch-coated and Ch-۳ kGy samples. After ۹ days of storage at ۴ºC, TVC was ۷.۳, ۶, ۵ and ۳.۸ log cfu/g respectively. There was a significant difference between the bioburden of control and irradiated samples with doses of ۳ kGy, ۵ kGy and ۷ kGy in Ch-coated and Ch- non coated samples. But there was no a significant difference between ۵ kGy and Ch-۳ kGy, and between ۷ kGy and Ch-۵ kGy samples. In control, ch-coated and ۳ kGy samples, initial S. aureus counts were ۳.۱, ۱.۹ and ۱.۶ log cfu/g which increased to ۴, ۲.۵ and ۲.۶ respectively. S. aureus was not detected in other samples. In control and ch-coated samples, initial E. coli counts were ۲.۴ and ۱.۵ cfu/g which increased to ۱۱ and ۱.۹ respectively. Salmonella spp. were only found in non-irradiated and ch-coated samples. It has been suggested that the mechanism of antibacterial activity of chitosan in Gram negative bacteria is disruption of the LPS layer of the outer membrane, and its action against S. aureus is due to increasing in membrane permeability, which leads to the leakage of cell inclusions.CONCLUSIONThe results showed gamma radiation and chitosan had a great effect on reducing the initial bioburden of samples below the standard limit up to ۷ days. Moreover, chitosan decreased the required absorbed dose to reach specific bioburden level. Therefore, gamma irradiation can be a valuable tool to reduce the economic losses related to the microbial spoilage. Since gamma radiation also affects biochemical and appearance characteristics, the optimal dose should be selected based on the results of a comprehensive investigation of the effect of gamma radiation on meat.