Analysis of peptide fraction from white wines

Abstract

Among nitrogen compounds included in white wines, the peptide fraction is certainly the least studied, however this fraction is quantitatively the most important (Feuillat, 1974). Existing studies concern the fraction below 1 kDa and only for white and sparkling wines (Bartolomé et al, 1997, Desportes et al 2000). In this report, we have developed methods to isolate peptides from reference white wines. Then, we have applied this methodology with bitter wine to answer a research question: is there a relation between peptides and the bitterness of white wine as for some cheese for example (Furtado, 1984)? First, after splitting reference wines by means of tangential ultrafiltration we got 3 different fractions: proteins above 10 kDa, peptides between 3 and 10 kDa and small peptides and free amino acids below 3 kDa. The amount of total nitrogen for each fraction was quantified by method of Kjedhal. We confirm that peptides represent the largest fraction of the nitrogen compounds in white wine. We expanded the range of molecular weight and studied the peptide fraction between 1 kDa and 10 kDa. This fraction of interest obtained by tangential ultrafiltration was diafiltrated against water and was concentrated by lyophilization. After, extracts from this fraction was separated by gel exclusion chromatography with the superdex 30 specific for peptides. Each fraction was read by absorbance at the 275 nm and then specifically detected by fluorescence with o-phtalaldehyde (OPA) to differentiate peptides from other molecules like polyphenols which are also detected at this wavelength. This isolation strategy was subsequently applied to white wines more or less bitter to investigate a potential relation between the peptides and the bitter taste. We obtained different peptide profiles between the most and least bitter wine for peptides corresponding to a high molecular weight. Every white wines studied here have similar peptide profiles made of two pools of different peptides. For the bitterest wine, the first pool corresponding to the higher molecular weight is greater. Thus, we may have revealed a relation between a class of peptides and the bitterness of these white wines.

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