Characterization of phenolic compounds biosynthesized in pink-colored skin of Japanese indigenous Vitisvinifera cv. Koshu grape

Vitis vinifera cv. Koshu is a traditional grape cultivar that has been grown for centuries in Japan. The Koshu grape has pink-colored skin and Koshu wines have slight astringency. We demonstrated for the first time the characterization of hydroxycinnamic acids, flavan-3-ols, and flavonoids in Koshu grape using high-performance liquid chromatography and liquid chromatography–mass spectrometry. The gross weight of phenolic compounds excluding anthocyanins and proanthocyanidins in Koshu grape at harvest was higher than those in Sauvignon Blanc, Chardonnay, and Merlot grapes. In addition, hydroxycinnamic acid and monomeric flavonol contents in Koshu grape were also higher than those in the other grape cultivars. Transcription analysis of cinnamic acid 4-hydroxylase, p-coumarate 3-hydroxylase, caffeate methyltransferase, and flavonol synthase genes indicated high accumulation of hydroxycinnamic acids and flavonols in Koshu grape skin compared with the other cultivars. These findings obtained by chemical and molecular approaches partially explained the phenolic characteristics and the peculiar astringency of Koshu grape.