Development of a LC-FTMS method to quantify natural sweeteners in red wines

Abstract

The quality of a wine is largely related to the balance between its sourness, bitterness and sweetness. Recently, molecules coming from grapes have been showed to notably contribute to sweet taste of dry wines. To study the viticultural and oenological parameters likely to affect their concentration, their quantification appears of high interest and subsequently requires powerful analytical techniques. 

Therefore, a new method using liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS) was developed and validated to quantify epi-DPA-3′-O-β-glucopyranoside acid (epi-DPA-G) and astilbin, sweet molecules identified in wine. Three gradients were tested on five different C18 columns (Hypersil Gold, HSS T3, BEH, Syncronis and Kinetex). 

The finest results were obtained upon using Hypersil Gold C18 and a gradient elution composed of 0.1 % formic acid in water and 0.1 % formic acid in acetonitrile. Satisfactory linearity with correlative coefficient (r2) higher than 0.995 was achieved for both compounds with recoveries higher than 89 %. Good sensitivity (LOD ≤ 7 μg L-1) and repeatability (RSD ≤ 3 %) were obtained. 

The developed method was applied to screen epi-DPA-G and astilbin in red wines coming from several vintages over one century. Both compounds have been detected in all wines, at concentrations varying from 1.4 to 14.7 mg L-1 for epi-DPA-G and from 0.5 to 32.2 mg L-1 for astilbin. These results demonstrate the reliability of the developed method to quantifiy epi-DPA-G and astilbin in wine and suggest their oenological interest. Moreover, the method was used to study the influence of various winemaking parameters on epi-DPA-G and astilbin concentrations. The results opened promising perspectives for a better monitoring of extraction during vatting.