Enological functions of the parietal yeast mannoproteins (intervento orale)

Mannoproteins, that constitute 25-50% of the cell wall of Saccharomyces cerevisiae, are located in the outermost layer of yeast cell wall, where they are connected with a matrix of amorphous β-1,3 glucan. Mannoproteins determine the wall's porosity and regulate leakage of proteins from the periplasmic space and entrance of macromolecules from the environment.Parietal yeast mannoproteins carry out various enological functions:- They are partially released during alcoholic fermentation and, especially, during on-lees ageing. Contact time, temperature, and agitation of the yeast biomass promote their release, due to an enzymatic autolysis of the lees: β-glucanases present in the cell-wall hydrolyze the parietal glucans-anchor points [1].- They are capable of combining with phenolics, thus diminishing the total polyphenol index [2]; this mechanism can be exclusively physical, involving the establishment of weak and reversible interactions mainly between anthocyanins and yeast walls by absorption [3]. A recent paper has showed remarkable correlations between yeast strain used for winemaking and phenolic composition of wine, elucidating that strain behaviour can somewhat modify chromatic properties, phenolics profile and antioxidant power of wine [4].- They could play a role in the ochratoxin A adsorption from contaminated musts, due to the mycotoxin-binding capacity reported for modified mannanoligosaccharide derived from the cell wall of S. cerevisiae [5]. Regarding ochratoxin A removal, different decontamination procedures based on Saccharomyces strains were recently proposed [6-8].- They can exhibit a net negative charge when they are composed also of acidic oligosaccharides containing mannosylphosphate; this modification depends on the strain background and can change the properties and environment of the cell surface [9].Further developments of studies on enological function of mannoproteins are foreseeable.References[1] R.M. Llaubères, D. Dubourdieu and J.C. Villetaz. J. Sci. Food Agric. 41 (1987), p. 277[2] P. Chatonnet, D. Dubourdieu and J.N. Boidron. Sci. Aliments 12 (1992), p. 666.[3] Y. Vasserot, S. Caillet and A. Maujean. Am. J. Enol. Vitic. 48 (1997), p. 433.[4] A. Caridi, A. Cufari, R. Lovino, R. Palumbo, I. Tedesco. Food Technol. Biotechnol. 42 (2004), p. 37.[5] G. Devegowda, M.V.L.N. Raju and H.V.L.N. Swamy. Feedstuffs 70 (1998), p. 12.[6] M. Piotrowska and Z. Zakowska. Food Biotechnol. 17 (2000), p. 307[7] H. Bejaoui, F. Mathieu, P. Taillandier and A. Lebrihi. J. Appl. Microbiol. 97 (2004), p. 1038[8] A. Caridi, A. Cufari, F. Galvano, M. Geria, S. Postorino, A. Tafuri and A. Ritieni. 19th International ICFMH Symposium, Portorož , Slovenia (2004), p.264[9] Y. Jigami and T. Odani. Biochim. Biophys. Acta 1426 (1999), p. 335