Taste-guided isolation of sweet-tasting compounds from grape seeds, structural elucidation and identification in wines

This work aimed at improving knowledge about sweetness in dry wines. Following on from the empirical observations of winegrowers, we assessed the contribution of grape seeds to wine sensory properties. An inductive fractionation method guided by gustatometry was used to isolate and characterize sweet-tasting compounds from grapes. Fractionation of grape seed macerates was achieved by liquid-liquid extraction, centrifugal partition chromatography (CPC) and preparative HPLC. Then, the structures of the purified compounds were elucidated by use of FTMS and NMR. Five compounds were identified: two new compounds, 2-hydroxy-3-methylpentanoic-2-O-β-glucopyranoside (H3MP-G) and 2-hydroxy-4-methylpentanoic-2-O-β-glucopyranoside acids (H4MP-G), along with gallic-4-O-β-glucopyranoside acid (AG-G), 3-indolyl-(2R)-O-β-d-glycoside lactic acid (ILA-G) and epi-DPA-3′-O-β-glucopyranoside acid (epi-DPA-G). These compounds exhibited various levels of sweetness in a hydro-ethanolic solution and in white and red wines. Additionally, H3MP-G, H4MP-G and epi-DPA-G were identified for the first time in grapes and wines, whereas AG-G has already been reported in white grapes but never in wine.