Preliminary characterisation of mannoproteins from different wine yeast strains and impact on wine properties

Mannoproteins (MPs) are released from the yeast cell wall during alcoholic fermentation and aging on the lees, and influence aspects of wine quality such as haze formation and colour stability. Yet, as this is a slow process with microbiological and sensory risks, the exogenous addition of extracted MPs poses an efficient alternative. While Saccharomyces cerevisiae has long been studied as a prominent source for MPs extraction, their structure and composition greatly differ between yeast species. This may influence their behaviour in the wine matrix and subsequent impact on wine properties. However, although wine yeast species other than S. cerevisiae possibly present an untapped source of MPs, they are still ill-characterised in terms of chemical composition and influence on wine. This study aimed to characterise the composition of MPs extracted from different wine yeast strains, and to investigate the impact of their addition on wine properties of organoleptic significance. MPs extracted and purified from four strains belonging to four different species (Saccharomyces cerevisiae, Saccharomyces boulardii, Metschnikowia fructicola and Torulaspora delbrueckii) were subjected to HR-SEC and GC-MS analyses to determine polysaccharide size distribution and monosaccharide composition, respectively. After addition of these MPs to Cabernet Sauvignon and Chardonnay wines, samples taken over the course of 6 months were analysed for protein stability, colour stability, browning potential and astringency. HR-SEC analyses of the MPs revealed differences in size distribution patterns between species both in terms of the maximum and the medium molecular weight observed. MPs impact on the four different wine parameters tested were dependent on several factors, including time since MPs addition, and the yeast strain of origin. For example, whereas the addition of MPs from S. cerevisiae and S. boulardii showed increased white wine protein stability after 3 months, M. fructicola and T. delbrueckii did not. The results obtained in this study form an important step towards further characterisation of mannoproteins derived from non-Saccharomyces yeast species. While the variable impact of MPs from different species on wine properties is an important aspect to consider in winemaking applications, further information regarding the influence of variations in MPs structure and composition could be used to better understand this effect.