Microbial and enzymatic transformation of some polyphenolic compounds

The main goal of the thesis is the transformation of hesperidin and quercetin compounds by using microorganisms and enzymes. Based on these compounds, it aims to convert compounds difficult or impossible to synthesize by classical chemical methods into value-added metabolites by biotransformation. Within the scope of the thesis, hesperidin and quercetin are subject to microbial and enzymatic transformation studies using 25 different microorganisms and a laccase enzyme, respectively. As a result of biotransformation studies, six metabolites were found in quercetin and eight metabolites in hesperidin. The microbial transformation of quercetin and the structure of three metabolites, resveratrol, isorhamnetin and protocatechuic acid, were elucidated by LC/MS-MS. Enzymatic transformation of quercetin via laccase was obtained to 2-(3,4-dimethoxyphenyl)-3,5-dihydroxy-7-methoxy-chroman-4-one (M5) and 3-hydroxy-2-(4-hydroxyphenyl)-7-methoxy-5-methyl-chroman-4-one (M6). Resveratrol, isorhamnetin, M5 and M6 metabolites were obtained for the first time by quercetin's microbial and enzymatic transformation. The structure of pinocembrin and naringenin in the microbial transformation of hesperidin was elucidated by LC/MS-MS. Eriodictyol and hesperetin were isolated, and molecular structure was defined by NMR and mass spectrum. Pinocembrin, eriodictyol and naringenin were obtained for the first time by microbial transformation of hesperidin. The metabolite obtained from the enzymatic transformation of hesperidin with laccase was identified as naringinin due to LC/MS-MS analysis. The biological activities of the substrates, the biotransformation extracts and the metabolites were examined in the in vitro 5-lipoxygenase (LOX) enzyme inhibition, antioxidant, antimicrobial, and acute toxicity activities. The antimicrobial activity of both hesperetin and naringenin against S. aureus is higher than hesperidin. Resveratrol, one of the quercetin metabolites, was found to be more effective than quercetin against Salmonella typhimurium (62.5 µg/mL) and Bacillus licheniformis (62.5 µg/mL) strains. The antimicrobial activity of hesperetin and naringenin against Staphylococcus aureus was higher than hesperidin. According to this result, biofilm and synergy-biofilm of hesperetin and naringenin were carried out against S. aureus. The checkerboard method in biofilm was done for the first time, and the technique was developed. These two compounds showed synergistic activity (FIKI value 1.063). In the acute toxicity study with the Brine Shrimp method, the highest effect was found in resveratrol.