# Effects of Chitosan Coatings on Controlling
## 4 Discussion
In fact, the aerobically stored chitosan-coated meat pieces had lower _L. monocytogenes_ counts by 1 log\({}_{10}\) CFU/g on the last day of storage, compared to the vacuum-packaged pieces. The antimicrobial activity of chitosan against _L. monocytogenes_ is possibly due to the electrostatic interaction between the NH\({}^{3+}\) groups of chitosan and the negatively charged phosphonyl groups of the phospholipid components of the _Listeria_ cell membrane [47]. Apart from beef and mutton, many researchers have demonstrated the antimicrobial activity of chitosan against _S. aureus_ and _L. monocytogenes_ in other types of meat. [PERSON] et al. [48] reported a 1-log\({}_{10}\) decrease in the counts of _L. monocytogenes_ in chicken pieces coated with 2% chitosan and stored under refrigeration. [PERSON] et al. [33] also observed that chitosan-coated (2%) chicken seekkhab had 2-3-log\({}_{10}\) CFU/g lower staphylococcal counts compared to the controls. Regarding pork, [PERSON] et al. [42] reported a 3-log\({}_{10}\) and a 2-log\({}_{10}\) reduction in the counts of _L. monocytogenes_ in chitosan-coated (1%) smoked pork neck and ham, respectively. Similarly, [PERSON] et al. [49] concluded that chitosan solution (0.5%) lowered the staphylococcal counts of fresh chilled pork by 1 log\({}_{10}\) CFU/g, and that the combination of chitosan with nisin and tea polyphenols extended the shelf life of fresh chilled pork by up to 11 days. Regarding the different meat types (beef or mutton), statistically significant differences were observed only in _Staphylococcus aureus_-spiked meat pieces, with the difference being statistically significant after the 14 th day of storage. Beef pieces had lower _S. aureus_ counts than mutton pieces. In contrast, _L. monocytogenes_-spiked meat pieces did not show any differences between meat types. _S. aureus_ can readily colonize both beef and mutton meat, as shown by [PERSON] et al. [50], who reported that the prevalence of _Staphylococcus aureus_ in beef and sheep carcasses was comparable. Still, small differences in meat composition have been reported to alter the growth potential in these two meat types. It is possible that differences in the meats' pH may be the cause, as evidenced by [PERSON] et al. [51], who reported that a rather consistent 0.41 pH difference between beef and lamb had an effect on bacterial growth rates. This difference is expected to be more profound in _S. aureus_- than in _L. monocytogenes_-spiked meat pieces, since _S. aureus_ is rather sensitive at low pH values [52], whereas _L. monocytogenes_ exhibits greater tolerance at pH levels lower than 4.5 during cold storage [53]. Nevertheless, this hypothesis needs to be further explored. Regarding the choice of aerobic storage or vacuum-packaging, little-to-no synergistic effect was observed on either beef or mutton meat pieces. A similar observation was reported by [PERSON] et al. [54], who found no significant difference between vacuum-packed and chitosan-coated vacuum-packed chicken burgers, stating that the effect of chitosan surpassed the effect of vacuum-packaging. Similarly, [PERSON] and [PERSON] [35] reported that the combination of chitosan coating and vacuum-packaging was more effective than vacuum-packaging alone. In contrast, [PERSON] et al. [55] reported a synergistic effect of vacuum-packaging and chitosan in minced trout fillets against the microbial indicators examined. As already mentioned, the main antimicrobial mechanisms of chitosan on _S. aureus_ and _L. monocytogenes_ are probably different, with chitosan restricting membrane diffusion in _S. aureus_[23], whereas it forms electrostatic interactions in _L. monocytogenes_[47]. The observed lack of differences in _S. aureus_ counts between aerobic and vacuum-packed meat pieces may justify the proposed mechanism of chitosan's antimicrobial activity.