Isolation and Structural Characterization of New Anthocyanin-Derived Yellow Pigments in Aged Red Wines

TLDR

Two novel yellow pigments were isolated from aged Port wine using TSK Toyopearl HW‑40(s) gel chromatography and characterized by UV‑vis, 1H/13C NMR, and LC‑ESI/MS. The pigments exhibit a 478‑nm absorption peak, a hypsochromic shift giving a yellow hue, and are identified as methyl‑linked pyranomalvidin 3‑glucoside and its coumaroyl glucoside derivative formed by acetoacetic acid reacting with grape anthocyanins, marking the first isolation and NMR characterization of this new yellow pigment family in red wine. Keywords: red wine, aging, yellow color, anthocyanins, acetoacetic acid, methyl pyranoanthocyanins, isolation, NMR.

Abstract

Two newly formed yellow pigments that revealed unique spectral features were detected and isolated from an aged Port red wine by TSK Toyopearl HW-40(s) gel chromatography and characterized by UV−visible spectrophotometry, 1H NMR and 13C NMR, and mass spectrometry (LC-ESI/MS). The UV−vis spectra of these pigments showed maximum absorption at 478 nm that is significantly hypsochromically shifted from those of original grape anthocyanins and other pyranoanthocyanins, exhibiting a more yellow hue in acidic solution. The structures of these pigments correspond to methyl-linked pyranomalvidin 3-glucoside and its respective coumaroyl glucoside derivative. They were shown to arise from the reaction between acetoacetic acid and genuine grape anthocyanins. Isolation and NMR identification using 1D and 2D NMR techniques are reported for the first time for this new family of anthocyanin-derived yellow pigments occurring in red wines. Keywords: Red wine; aging; yellow color; anthocyanins; acetoacetic acid; methyl pyranoanthocyanins; isolation; NMR