Yeasts, mannoproteins and wine quality

Mannoproteins represent one of the main components of the yeast cell wall and they can be released in the media during alcoholic fermentation and wine aging on lees. Numerous scientific works have shown that mannoproteins have many positive effects on wine quality, as they contribute to reduce protein and tartrate instability, to improve the mouthfeel and fullness, to decrease the perception of astringency, to increase sweetness and roundness and to retain aromatic compounds. Moreover, mannoproteins can adsorb toxic compounds such as ochratoxin A, improve the foam quality of sparkling wines and stimulate malolactic fermentation by lactic acid bacteria. While Saccharomyces cerevisiae generally releases low amounts of mannoproteins, normally ranging from 50 to 150 mg/L, non-Saccharomyces wine yeasts, such as those ascribed to the genera Candida, Hanseniaspora, Lachancea thermotolerans, Metschnikowia, Pichia, Saccharomycodes, Torulaspora, and Zygosaccharomyces, may release up to 600 mg/L of mannoproteins during the alcoholic fermentation, and even higher amounts (approximately 3-7 times more than S. cerevisiae) for the yeasts belonging to the genus Schizosaccharomyces. In any case, wide biodiversity for this characteristic is observed within each genera. Indeed, many non-Saccharomyces yeasts have been proposed to be used in combination with Saccharomyces yeasts in winemaking to obtain wines with a more complex aroma and the possibility to increase the content of mannoproteins by the use of non-Saccharomyces yeasts could represent an added value to the interest towards these wine yeasts.