Antimicrobial and antioxidant properties of chitosan
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The effect of chitosan as coatings for evaluating the antimicrobial and antioxidant effects on raw oysters was evaluated over a 12 to 15-day storage at 4 ºC. Four chitosan concentrations were prepared: 0.0, 0.5, 1.0 and 2.0%.Uncoated samples served as the control. Samples were then subjected to microbial and chemical examination. The growth of Staphylococcus aureus cells was inhibited by all treatments on day 15, After pre-enrichment. Thus, the effectiveness of chitosan against S. aureus was not very clear when the pre-enrichment step was included. Similarly, the growth inhibition of S. aureus by chitosan was studied without pre-enrichment of samples with the storage time reduced to 12 days. Cells were most sensitive to chitosan at 2.0% concentration, followed by 0.5% and 1.0%. Hence, 2.0% chitosan emerged as the best treatment for the inhibition and inactivation of S. aureus in raw oysters. Raw oysters coated with different levels of chitosan showed no increase in the 2 – thiobarbituric acid reactive substances (TBARS) throughout the entire period of storage. Also, no significant differences were found among the various treatments. Thus, chitosan can be used as an antimicrobial agent but the antioxidant effect of chitosan should be measured by some other method than the TBARS test.