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

Kufa, Amanda (2019-04)

Thesis (MScAgric)--Stellenbosch University, 2019.

Thesis

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.

AFRIKAANSE OPSOMMING: Die wynbedryf word uitgedaag met sigbare en nie-sigbare wynafwykings, wat lei tot winsverliese as verbruikers sulke wyne verwerp. Die duidelikheid en kleur van wyn is noodsaaklik vir witwynverbruikers, aangesien dit 'n maatstaf van gehalte is. Die verpienking van witwyn en die vorming van proteïenwaas is van die mees algemene visuele defekte wat in die bedryf voorkom. Verpienking is 'n nie-wetenskaplike term wat die verandering in die natuurlike witwynkleur na 'n pienk kleur beskryf. Daar is baie spekulasies gemaak oor die oorsake van witwynpienk, maar daar is nog geen duidelike verklaring vir die verskynsel nie. Proteïenwaas in witwyn word veroorsaak deur die presipitasie van patogenese-verwante proteïene, naamlik thaumatien-agtige proteïene en chitinases. Terwyl bentoniet algemeen gebruik word as 'n beboetmiddel om proteïenheur te vermy, het dit 'n negatiewe effek op wynkwaliteit. Daar is dus 'n behoefte aan koste-effektiewe alternatiewe wat daarop gemik is om wyne van beide pienk- en proteïen-waasvorming te voorkom. Vorige studies het gerapporteer dat sommige gisstamme die vermoë het om proteïenhaarvorming te verminder, terwyl geen studies tot dusver die impak van gisstamme op wynpynering aangemeld het nie. In hierdie studie is 'n mikrobiologiese gebaseerde oplossing ondersoek deur die gebruik van Saccharomyces cerevisiae en ander wynverwante gisspesies as alternatiewe vir chemies gebaseerde boete-middel. Monokultureerde en opeenvolgende geinokkuleerde fermentasies is uitgevoer in beide Sauvignon blanc-moes en sintetiese druiwe moes, en gisselmuurkitien- en mannoproteïenvlakke is tydens fermentasie gemonitor. Interessant genoeg het gisselmuurkitien- en mannoproteïenvlakke met meer as die helfte aan die einde van alkoholiese fermentasies vanaf die aanvanklike dag 1-vlakke afgeneem. 'n Baie belowende korrelasie is verkry tussen chitien in die gisselwand en die binding van GFP-getikte chitinases aan die selle. Verskillende gisstamme het verskillende bindingsaffiniteite vertoon, wat gebruik kan word om die waasbeskerming van 'n bepaalde stam te voorspel. Daar is ook 'n paar impak van gisstamme op pienking waargeneem. Ten slotte dui die data daarop dat die keuse van gisstamme kan help verminder, indien nie in sommige gevalle die behoefte aan die gebruik van bentoniet as 'n boete-agent vir proteïen-waasbeskerming uitskakel nie. Die data dui ook daarop dat pienking op soortgelyke maniere ietwat verminder kan word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105903
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