Abstract: This work was undertaken in order to study the antibacterial activity and underlying mechanism of eugenol-containing composite preservatives on Shewanella putrefaciens as the dominant spoilage bacterium in aquatic products. The composite preservatives tested included binary mixtures of eugenol with thymol, lactic acid, lysozyme (food-grade, 18 U/mg) and eugenol/lysozyme (biological-grade, 20 000 U/mg), while these compounds were used individually as controls. The morphological changes of bacterial cells before and after treatment with single and composite preservatives were observed by field emission scanning electron microscope (SEM) and transmission electron microscope (TEM). The cell membrane integrity and permeability, the degree of cell membrane damage and the activities of Na+, K+-ATPase and AKPase in the cell membrane of S. putrefaciens were determined. The results showed that eugenol had good antibacterial properties against S. putrefaciens, and could cause distortion, shrinkage, collapse or even significant dissolution of the cell membrane. The cell membrane structure was damaged to a certain extent, resulting in poor membrane integrity, increased membrane permeability and decreased Na+, K+-ATPase/AKPase activities. In combination with thymol, lactic acid, food-grade lysozyme and biological-grade lysozyme, eugenol showed a synergistic antibacterial effect, causing more serious damage to bacterial cell structure and consequently leading to poorer membrane integrity, a greater increase in membrane permeability and a significant decrease in Na+, K+-ATPase/AKPase activities (P < 0.05). The knowledge obtained in this study can provide a reference for the research and development of new preservatives for aquatic products.

Key words: Shewanella putrefaciens; eugenol; composite preservatives; antibacterial mechanism