Identification of Antibacterial Compounds From Yeast-Fermented Green Tea Leaf Extract via Bioautography and GC-MS

초록

Green tea polyphenols exhibit a range of biological activities, including antimicrobial effects, which can be further enhanced through microbial fermentation. To investigate this enhancement, this study examined the antibacterial activity of green tea leaf extract fermented with Saccharomyces cerevisiae and identified its major active compounds. Green tea leaf powder was fermented with S. cerevisiae KFRI 122 at 35 degrees C for 5 days in water without additives. The antibacterial activity of the yeast-fermented extract was compared with that of a nonfermented ethanol extract against nine food-borne pathogenic bacteria, based on determinations of minimum inhibitory concentration and minimum bactericidal concentration values. Yeast fermentation increased total phenolic and flavonoid contents and improved antibacterial activity relative to the heat-treated (nonfermented) extract, particularly against Bacillus licheniformis, Staphylococcus aureus, and Vibrio parahaemolyticus. The active antibacterial fraction was confirmed by TLC-based bioautography and subsequently analyzed by GC-MS. Caffeine, catechin, gallic acid, epigallocatechin, and epicatechin were identified in the active antibacterial fractions from both ethanol and fermented extracts. Yeast fermentation altered the composition of the extract, as revealed by GC-MS analysis, by reducing saccharide content and increasing the relative proportion of phenolic compounds. Notably, the active fractions from both extracts showed stronger inhibitory activity against V. parahaemolyticus than grapefruit seed extract. These findings demonstrate that yeast fermentation is an effective strategy for improving the antibacterial potential of green tea extracts and support the development of natural antibacterial agents.

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