Abstract: The bacteriostatic effects of kojic acid against the dominant spoilage bacteria Pseudomonas sp., Aeromonas sp. and Brochothrix thermosphacta and the pathogenic bacterium Salmonella sp. in chilled duck meat were studied by determining the diameter of inhibition zone, growth curves in LB liquid medium and minimal inhibitory concentration (MIC). The underlying mechanism was explored by analyzing the effect of kojic acid on the cell membrane and intracellular substances. The results showed that kojic acid had good bacteriostatic properties against all four strains. Brochothrix thermosphacta was sensitive to kojic acid treatment with an MIC of 0.5 mg/mL, and its growth in the liquid medium was completely low concentration of kojic acid. The diameter of zone of inhibition of Salmonella, Pseudomonas, and Aeromonas increased significantly with the increase of kojic acid concentration, with an over 2-fold increase being observed for Pseudomonas and Aeromonas. Kojic acid treatment at 2.0 mg/mL could completely inhibit the growth of all above 3 strains in the liquid medium. Kojic acid treatment could increase cell surface hydrophobicity by two to three folds, reduce the selective permeability of the cell membrane, and destroy the structure of the cell membrane, thereby leading to increased levels of extracellular Ca2+, K+ and Mg2+. Kojic acid treatment could also destroy respiratory chain dehydrogenase activity, and result in the leakage of intracellular β-galactosidase and alkaline phosphatase and cell membrane rupture to form pores. Besides, kojic acid treatment caused a significant increase in extracellular protein content, with a simultaneous decrease in intracellular proteins with molecular mass more than 66.4 kDa and less than 20 kDa. Overall, kojic acid inhibited the four strains via the same mechanism, namely, by promoting hydrophobic substance exposure, destroying related enzyme activities and changing cell membrane permeability, as well as disturbing protein metabolism.

Key words: chilled duck meat, kojic acid, spoilage bacteria, bacteriostatic characteristics, antibacterial mechanism