Polyphenol targeted and untargeted metabolomics on rosé wines : impact of protein fining on polyphenolic composition and color

Abstract

Color is one of the key elements in the marketing of rosé wines[1]. Their broad range of color is due to the presence of red pigments (i.e. anthocyanins and their derivatives) and yellow pigments, likely including polyphenol oxidation products. Clarifying agents are widely used in the winemaking industry to enhance wine stability and to modulate wine color by binding and precipitating polyphenols[2]. During this study, the impact of four different fining agents (i.e. two vegetal proteins, potatoe and pea proteins, an animal protein, casein, and a synthetic polymer, polyvinylpolypyrrolidone, PVPP) on Syrah Rose wine color and phenolic composition (especially pigments) was investigated. Color was characterized by spectrophotometry analysis using the CIELab system in addition to absorbance data. Fining using PVPP had the highest impact on redness (a*) and lightness (L*) parameters, whereas patatin strongly reduced the yellow component (b*) of the wine color. In parallel, the concentration of 125 phenolic compounds including 85 anthocyanins and derived pigments was determined by Ultra High Performance Liquid Chromatography coupled to elestrospray ionisaion triple-quadrupole Mass Spectrometry (UHPLC-QqQ-ESI-MS) in the Multiple Reaction Monitoring mode[3] . Results confirmed the affinity of PVPP towards flavan-3-ols and anthocyanins, especially coumaroylated anthocyanins demonstrated earlier[4]. Chemometrics analysis of the color and composition data revealed a link between redness (a*) and lightness (L*) related to native anthocyanin and flavan-3-ol concentrations. However, no specific marker was associated to patatin fining, suggesting the involvement of other pigments in the yellow component (b*). Additional data was acquired on the same set of samples by untargeted metabolomics using Ultra High Performance Liquid Chromatography coupled to an High Resolution Mass Spectrometer (UHPLC-HR-MS). Our results corroborate those of targeted analysis, demonstrating particular affinity of PVPP for native anthocyanins and flavan-3-ol but also flavonols and stilbenes. Markers of each fining treatment were also identified. PVPP fining treatment revealed a sharp decrease in the rose wine color, especially on the redness (a*) component linked to losses of phenolic compounds such as native anthocyanin. Further investigations aiming at revealing markers of the yellow component (b*) from untargeted analysis data are under way.