Evaluation of bio-guided fraction from Laminaria japonica as a natural food preservative based on antimicrobial activity

Abstract

Foodborne pathogens cause foodborne diseases and pose a major food safety challenge to the food industry. The aim of this study was to evaluate the antimicrobial activity of Laminaria japonica extract against foodborne pathogens, to optimize the extraction of antimicrobial substance, and to investigate the antimicrobial mechanism. L. japonica ethanol extract exhibited significant (P < 0.05) antimicrobial activities against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Proteus vulgaris, Enterobacter aerogenes and Candida tropicalis. The minimum inhibitory concentration (MIC) values ranged from 0.26 ± 0.10 to 1.67 ± 0.72 mg/mL. Based on the results of antimicrobial activity assay and MIC test, E. coli was used as the represented pathogen to optimize extraction conditions, and to perform the bio-guided assay and investigate the antimicrobial mechanism. An L27(313) orthogonal array design was employed to obtain high levels of antimicrobial substance production. The optimum conditions were extraction temperature 80 °C, extraction time 4 h, and ratio of solid to liquid 1:10 (g/mL). The bio-guided assay showed that dichloromethane fraction from L. japonica ethanol extract (DFL) exhibited the strongest (P < 0.05) antimicrobial activity. The major compounds of DFL were palmitic acid (42.55%), oleic acid (17.40%), and myristic acid (17.31%). Treatment with DFL caused obvious morphological and ultrastructural changes, cytomembrane disruption, membrane depolarization, accumulation of reactive oxygen species (ROS), inhibition of ATPase activity, reduction of DNA content, and subsequently destruction of the cell cycle. Our findings demonstrate that the cell membrane is a primary target of DFL action on E. coli and L. japonica ethanol extract has promising potential as a natural food preservative.