H OH metabolites OH Article Flavan-3-ols Content in Red Raspberry Leaves Increases under Blue Led-Light Irradiation Ryo Kobori 1, Seiya Hashimoto 2, Hayato Koshimizu 2, Shuich Yakami 1, Mizuki Hirai 1, Kenta Noro 1, Takashi Kawasaki 3 and Akiko Saito 1,2,* 1 Graduate School of Engineering, Osaka Electro-Communication University (OECU), 18-8 Hatsu-cho, Neyagawa-shi, Osaka 572-8530, Japan; [email protected] (R.K.); [email protected] (S.Y.); [email protected] (M.H.); [email protected] (K.N.) 2 Faculty of Engineering, Osaka Electro-Communication University (OECU), 18-8 Hatsu-cho, Neyagawa-shi, Osaka 572-8530, Japan; [email protected] (S.H.); [email protected] (H.K.) 3 Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Kyoto 611-0011, Japan; [email protected] * Correspondence: [email protected]; Tel.: +81-72-824-1131 Received: 22 February 2019; Accepted: 20 March 2019; Published: 21 March 2019 Abstract: Berry fruits are well known to contain large amounts of polyphenol compounds. Among them, flavan-3-ol derivatives are a group of secondary metabolism compounds currently attracting a great deal of attention owing to their health benefits. Not only the fruits, but also the leaves of raspberry plants, are highly esteemed for tea making around the world and are largely used for food. In this report, we discuss the results of our study on the effect of light and temperature on polyphenol accumulation in raspberry leaves. When raspberry was cultivated in a plant factory unit and light intensity, wavelength, and temperature were varied, the amount of total polyphenol increased under blue light. Quantitative determination of (+)-catechin, (–)-epicatechin, procyanidin B4, flavan-3-ol trimer, which are flavan-3-ol derivatives, was carried out using HPLC, whereby we confirmed their increase under blue light. Semi-quantitative RT-PCR showed correlation between chalcone synthase (CHS) gene expression and the amounts of the compounds measured in the leaves. Keywords: polyphenols; light; temperature; controlled environment; biosynthesis; leaf extracts; HPLC; structure-function relations 1. Introduction There is currently great interest in the investigation of compounds from food sources with biological activities, as they are generally considered highly safe because they are consumed as part of the general daily diet. In particular, polyphenols contained in many health foods, as well as in vegetables and fruits, are thought to have various health benefits [1,2]. Among them, flavan-3-ol derivatives are general plant-derived physiologically active compounds known to be highly functional. In particular, the main ingredient of green tea-polyphenols shows various moderate bioactivities without severe toxicity and its health promoting effects have been extensively studied. Although various biologically active flavan-3-ol derivatives are present as minor constituents in plants as well as in green tea, their biological activities have yet to be revealed, mainly owing to their relative unavailability. Therefore, the development of new methods to elucidate the biosynthesis pathway, polymerization mechanisms, and transport of flavan-3-ol derivatives has become an important and active field of research [3,4]. Especially, developing a method to control the biosynthesis of flavan-3-ol derivatives with strong biological activities in plants would be a tool of great value to produce highly functional plants and foods. Metabolites 2019, 9, 56; doi:10.3390/metabo9030056 www.mdpi.com/journal/metabolites Metabolites 2019, 9, x 2 of 14 Metabolites 2019, 9, 56 2 of 14 The production of polyphenolic compounds is affected by light irradiation, and it is thought that this can be used to increase the amount of polyphenol secondary metabolites, including flavanThe-3-ol production derivatives of. polyphenolicFor example, compounds short-term isultraviolet affected by C light irradiation irradiation, was andshown it is thoughtto stimulate that biosyntheticthis can be used pathways, to increase leading the amountto enhancement of polyphenol of the secondaryaccumulation metabolites, of polyphenol including compounds flavan-3-ol [5]. 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