Browsing by Author "Kufa, Amanda"

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    A microbiological solution to visible wine defects : pinking and protein haze formation
    (Stellenbosch : Stellenbosch University, 2019-04) Kufa, Amanda; Bauer, Florian; Ndlovu, Thulile; Van Jaarsveld, Francois; Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.
    ENGLISH ABSTRACT: The wine industry is challenged with visible and nonvisible wine defects, which result in profit losses as 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 the most frequent visual defects encountered in the industry. Pinking is a non-scientific term that describes the change in the natural white wine colour to a pink colour. Many speculations have been made concerning the causes of white wine pinking, but there is no conclusive explanation for the phenomenon yet. Protein haze in white wine is caused by the precipitation of pathogenesis-related proteins, namely thaumatin-like proteins, and chitinase. While bentonite is commonly used as a fining agent to avoid protein haze, it has an adverse effect on wine quality. There is, therefore, a need for cost-effective alternatives aimed at preventing wines from both pinking and protein haze formation. Previous studies have reported that some yeast strains have the capability of reducing protein haze formation while no studies to date have reported the impact of yeast strains on wine pinking. In this study, a microbiological based solution was explored and the use of Saccharomyces cerevisiae and other wine-related yeast species as alternatives to chemically based fining agents was investigated. Monocultured and sequentially inoculated fermentations were carried out in both Sauvignon blanc must and synthetic grape must, and yeast cell wall chitin and mannoproteins levels were monitored during fermentation. Interestingly, yeast cell wall chitin and mannoproteins levels decreased by more than half at the end of alcoholic fermentations from the initial day 1 level. A very promising correlation was obtained between chitin in the yeast cell wall and the binding of GFP-tagged chitinase to the cells. Different stains showed different binding affinities, which could be used to predict the haze protection of a particular strain. 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 cases eliminate the need for the use of bentonite as a fining agent for protein haze protection. The data also suggest that pinking can be somewhat reduced in similar ways.