Effect of mannoproteins extracted from Torulaspora delbrueckii on wine flavanol composition and on flavanol-salivary protein interactions

Abstract

Global climate change is exerting an influence on vine phenology, leading to a decoupling of technological and phenolic maturity of grapes. This results in the modification of berry chemical composition, which can translate into wines with excessive astringency. The addition of mannoproteins (MP) to wine has been proposed as a way of mitigating this problem, since some studies have shown that MPs can modulate wine astringency. However, the mechanism underlying the astringency modulation effect of MPs is not well known and it seems to be dependent on the compositional and structural characteristics of the MP.

MPs are highly glycosylated proteins located in the outermost layer of the yeast cell wall. They are naturally released to the wine by actively growing yeast during alcoholic fermentation and by yeast autolysis during aging on lees. The commercial MP preparations, often used in an empirical way, are obtained from the cell wall of Saccharomyces cerevisiae, the main oenological yeast, to improve wine technological and sensory properties.

In wine, non-Saccharomyces yeasts, such as Torulaspora genre, predominate over S. cerevisiae during the initial phases of spontaneous alcoholic fermentations. However, little is known about the MPs of non-Saccharomyces yeasts and, unlike S. cerevisiae, they have never been considered as a possible source of MPs of oenological interest.

Thus, the objective of this work was to isolate and characterize MPs from the cell wall of Torulaspora delbrueckii and evaluate their effect on red wine astringency. The MPs were obtained from a commercial strain of T. delbrueckii (Lallemand, Inc.) by means of different treatments: induced autolysis and enzymatic and chemical hydrolysis. The MP extracts were characterized as follows. The protein content was determined by Lowry method and the (glycol)protein profile was analyzed by SDS-PAGE. The molecular weight of the MPs was determined by HRSEC-RID and its monosaccharide composition was analyzed after MP hydrolysis and derivatization followed by HPLC-DAD-MS analysis. To evaluate the possible effect of the obtained MPs on astringency, they were added to a red wine and changes in flavanol composition were assessed by HPLC-DAD-MS. In addition, the molecular basis of the MPs effect was also evaluated by studying the interactions between MPs, flavanols and salivary proteins by ITC.

The results showed differences in the structure and composition of the MPs extracted by the application of different treatments. Likewise, the study of the wine flavanol profile and of the MP-flavanol-salivary protein interactions suggested that T. delbrueckii can be a good source of mannoproteins with technological properties to modulate the wine flavanolic composition and the organoleptic properties related to these compounds.