Influence of mannoproteins on the volatility of fruity esters in Italian white wine

Mannoproteins (MPs) are yeast derived polysaccharides released in wine from yeast autolysis during alcoholic fermentation and wine ageing. They play important roles in wine quality and stability. In recent decades, there are theoretical speculations stating that added MPs could decrease the volatility and prolong the persistence of aroma active compounds (ACs) in wine, a desirable occurrence since aroma is a driver for wine quality. However, the MPs-ACs relationship is not yet fully understood as the conditions for its occurrence in real wines remain an unexplored field of research. Therefore, the aim of this thesis was to study the impact of added yeast’s MPs on the concentration of volatile fruity esters, compounds largely responsible for wine aroma profile, in white wine systems. To this end, an Italian still white wine from the Veneto region was used. Yeast MPs, produced by fermenting a model grape juice in a previous project, were characterised quantitatively (to determine protein concentration) using the BCA protein assay, qualitatively using the SDS-PAGE technique (to determine protein band mobility and sugar content) and analysed using HPSEC (to determine molecular weight distribution and concentration of polysaccharides) before being added, in a concentration of 400 mg/L, to the white wine from which macromolecules were preventively removed by ultra-filtration (MWCO 10 kDa). GC-MS was used to compare the concentration of the volatile fruity esters in the ultra-filtered (UF) wine with and without the addition of MPs. The results over a one month period of accelerated ageing showed that the addition of purified MPs at 400 mg/L did not cause significant effects (p < 0.05) in the different concentrations of fruity esters (ethyl isobutyrate, isoamyl acetate, ethyl octanoate, ethyl decanoate and phenylethyl acetate) except for ethyl hexanoate and ethyl butyrate in the treated wine samples when compared with control samples. Purified MPs had no effect in retarding hydrolysis of fruity esters in an UF Italian white wine system. This work was unable to determine whether these interactions will remain unchanged over time or their effect on the wine’s sensory profile. For this, further studies are recommended.