Analysis of Three Plant Extracts Components and Their Antibacterial Mechanisms Against Spoilage Bacteria in Sea Bass

To address the issue of microbial contamination and spoilage in sea bass, this study selected three plant extracts—oregano, citronella, and moringa. Their chemical compositions were analyzed by GC-MS, and active components were quantified. Antibacterial activities against Escherichia coli, Staphylococcus aureus, and Shewanella putrefaciens were evaluated by measuring inhibition zone diameters, growth curves, and MIC/MBC. Crystal violet staining, electrical conductivity measurement, and scanning electron microscopy were used to reveal the underlying mechanism. GC-MS analysis showed that oregano extract mainly contained phenols and quinones, citronella extract was dominated by aldehydes and terpenes, and moringa extract was mainly composed of esters and aldehydes, with a relatively diverse composition. Determination of active components showed that the total phenolic and total flavonoid contents of oregano extract were significantly higher than those of citronella and moringa extracts; Moringa extract was richest in total triterpenoids (3.05 mg/g); Total polysaccharide contents of citronella and moringa extracts were higher than that of oregano extract. Antibacterial activity evaluation showed that all three extracts could disrupt cell membrane integrity, increase electrical conductivity, and inhibit biofilm formation, but their antibacterial intensities differed significantly. Oregano extract had the broadest antibacterial spectrum and the strongest activity, with inhibition zone diameters greater than 12 mm against all three strains, and it showed the most significant inhibitory effects against E.coli and S.putrefaciens. Citronella extract exhibited the strongest inhibition against S. aureus, with an inhibition zone diameter of 14.05 mm. In contrast, moringa extract showed relatively mild antibacterial activity, with inhibition zone diameters not exceeding 10 mm and biofilm clearance rates below 50%. Correlation analysis indicated that the total phenolic content was significantly positively correlated with the total flavonoid content (r=0.82, P<0.05), and the two had a synergistic enhancing effect on antibacterial activity. The total phenolic content was positively correlated with the inhibition zone diameters against E.coli (r=0.50) and S.putrefaciens (r=0.43). The total triterpenoid content was positively correlated with the inhibition zone diameter against S.aureus (r=0.29). The antibacterial activities of the three plant extracts resulted from the synergistic effects of multiple active components, and their unique chemical compositions formed the basis of these activities. This study provides a theoretical basis for the development of natural plant-derived antibacterial agents for sea bass preservation.