Food Sci. Biotechnol. 24(5): 1817-1821 (2015) DOI 10.1007/s10068-015-0237-2 Research Note Lactobacillus plantarum-mediated Conversion of Flavonoid Glycosides into Flavonols, Quercetin, and Kaempferol in Cudrania tricuspidata Leaves Yuri Lee 1 , Jisun Oh 1,2, *, and Yong-Seob Jeong 1 1 Department of Food Science and Technology, Chonbuk National University, Jeonju, Jeonbuk 54896, Korea 2 Present address: School of Food Science and Biotechnology (BK21 plus), Kyungpook National University, Daegu 41566, Korea Introduction Cudrania tricuspidata (Carr.) Bureau, commonly called silkworm thorn, is a deciduous tree belonging to the Moraceae family. It is widely distributed in East Asia and has been used medicinally due to beneficial effects that are mainly attributed to biologically active compounds possessing strong antioxidant activities (1). Multiple studies have reported that silkworm thorn leaves and roots containing xanthones (2), glycoproteins (3), prenylated flavonoids (4), or flavonol glycosides (5) exhibited high levels of radical scavenging activity. Isoflavones and flavonoids were identified as the major components in Silkworm thorn fruit extracts (6,7). Thus, it is evident that almost all parts of silkworm thorn contain a variety of phenolic compounds that contribute to unique plant-based medicinal effects. In particular, silkworm thorn leaf ethanol or methanol extracts contain high levels of phenolic components (8), including kaempferol, kaempferol-7-O-β-D-glucopyranoside, and dihydroquercetin 7-O-β-D- glucopyranoside (9-11). Leaf extracts with strong antioxidant activities have shown inhibition of microbial growth and suppression of lipase activity (12,13). Dietary phenolic compounds and flavonoids are known to be bioactive with anti-oxidative activities, suggesting development of functional foods beneficial to human health (14-16). Flavonols are the dominant glycoside form in plants, usually as quercetin and kaempferol. These are versatile components due to biological activities (17-19). Flavonols are generally absorbed in the gastrointestinal tract as aglycones via passive diffusion (15). However, they may exist as aglycones in natural plants and food materials. Thus, numerous studies have investigated augmentation of aglycone levels based on removal of sugar groups from glycosides for the purpose of improving the bioavailability and/or functionality of plant flavonols (20,21). In this study, enhancement of quercetin and kaempferol aglycone contents in silkworm thorn leaves using Lactobacillus-mediated fermentation was studied. The antioxidant activities, and flavonoid and glycoside contents, of silkworm thorn leaves fermented using Lactobacillus plantarum were examined. Materials and Methods Plant materials, microorganisms, and fermentation of silkworm thorn leaves Dried silkworm thorn leaves (C. tricuspidata leaves, CTL) were purchased from a farm in Gimje, Jeollabuk-do, Korea in April of 2013. After grinding using a commercially available blender (Shinil Industrial Co., Ltd., Seoul, Korea), 100 g of CTL powder was suspended in 1 L of distilled water and sterilized using an autoclave at Received February 9 2015 Revised May 14 2015 Accepted June 2 2015 Published online October 31 2015 *Corresponding Author Tel: +82-53-950-5752 Fax: +82-53-950-6750 E-mail: j.oh@knu.ac.kr pISSN 1226-7708 eISSN 2092-6456 © KoSFoST and Springer 2015 Abstract High value-added food materials were developed based on enhancement of phenolic contents in Cudrania tricuspidata leaves using fermentation of silkworm thorn leaves with Lactobacillus derived from Korean soybean paste. Ethanol extracts from fermentates were examined for antioxidant activities and flavonoid and corresponding glycoside contents. Radical scavenging activities were increased by approximately 20% after fermentation. Two prominent spectral peaks in fermentates that increased in size, compared with non-fermentates, were identified as quercetin (m/z 301.1) and kaempferol (m/z 285.3). Three peaks that decreased in size in fermentates were identified as quercetin-7-O-beta-glucopyranoside (m/z 463.1), kaempferol-3- O-beta-glucopyranoside (m/z 447.1), and kaempferol-7- O-beta-glucopyranoside ( m/z 447.2). Conversion of flavonoid glycosides to flavonols, quercetin and kaempferol, occurred in silkworm thorn leaves due to fermentation with Lactobacillus. Keywords: Cudrania tricuspidata, Lactobacillus plantarum, fermentation, bioconversion, flavonoid glycoside