Protein Haze Formation in White Wines: Effect ofSaccharomyces cerevisiaeCell Wall Components Prepared with Different Procedures

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Cell wall material was extracted by five different methods from an oenological strain of Saccharomyces cerevisiae. Enzyme preparations containing beta-glucanase activity (Zymolyase, Glucanex, and Finizym 250L) allowed a better extraction yield compared to that of dithiothreitol (DTT) and EDTA. The yeast extracts were only soluble in part in wine. The wine-soluble fraction (WSF) of the five extracts, differing in both protein and sugar contents, when added in increasing amounts to white wine differently affected protein haze formation, as determined by the heat test, giving dose/response curves of different shapes. The curves obtained with the WSF derived from DDT and Zymolyase extracts showed a plateau value corresponding to 90% and 80% of wine haze reduction, respectively. In contrast, addition of the WSF derived from the other extracts resulted in increased turbidity with respect to the original wine. The mannoproteins (MP), isolated from each yeast extract by Concanavalin-A chromatography, gave dose/response curves showing shapes more similar among them than those obtained with the whole WSFs. The best wine stabilization was obtained with the MP of the DTT and Zymolyase extracts. The supernatants obtained after heating the MP of the different extracts were also tested. The stabilizing effect of the heat-stable MP (HSMP) was always larger than that of the corresponding total (un-heated) MP. The HSMP obtained starting from the DTT and Zymolyase extracts showed the best haze-protecting effect, which was, however, lower than that obtained with their corresponding WSF. This result suggests that wine protein stabilization by compounds of the yeast cell wall could be related, in addition to the action of the MP, also to the presence of other substances of different nature.