A microbiological solution to visible wine defects : pinking and protein haze formation

[摘要] ENGLISH ABSTRACT: The wine industry is challenged with visible and nonvisible wine defects, which result in profit lossesas consumers reject such wines. The clarity and color of the wine are essential to white wine consumers,as it is a measure of quality. Pinking of white wine and the formation of protein haze are some of themost frequent visual defects encountered in the industry. Pinking is a non-scientific term that describesthe change in the natural white wine colour to a pink colour. Many speculations have been madeconcerning the causes of white wine pinking, but there is no conclusive explanation for the phenomenonyet. Protein haze in white wine is caused by the precipitation of pathogenesis-related proteins, namelythaumatin-like proteins, and chitinase.While bentonite is commonly used as a fining agent to avoid protein haze, it has an adverse effect onwine quality. There is, therefore, a need for cost-effective alternatives aimed at preventing wines fromboth pinking and protein haze formation. Previous studies have reported that some yeast strains have thecapability of reducing protein haze formation while no studies to date have reported the impact of yeaststrains on wine pinking. In this study, a microbiological based solution was explored and the use ofSaccharomyces cerevisiae and other wine-related yeast species as alternatives to chemically based finingagents was investigated. Monocultured and sequentially inoculated fermentations were carried out inboth Sauvignon blanc must and synthetic grape must, and yeast cell wall chitin and mannoproteins levelswere monitored during fermentation.Interestingly, yeast cell wall chitin and mannoproteins levels decreased by more than half at the endof alcoholic fermentations from the initial day 1 level. A very promising correlation was obtainedbetween chitin in the yeast cell wall and the binding of GFP-tagged chitinase to the cells. Different stainsshowed different binding affinities, which could be used to predict the haze protection of a particularstrain. Some impact of yeast strains on pinking was also observed.In conclusion, the data suggest that yeast strain selection may help reduce, if not in some caseseliminate the need for the use of bentonite as a fining agent for protein haze protection. The data alsosuggest that pinking can be somewhat reduced in similar ways.

[发布机构] Stellenbosch University