Sensory, chemical and consumer analysis of Brettanomyces spoilage in South African wines

[摘要] ENGLISH ABSTRACT: This study focussed on the sensory effects of the main volatile compounds produced byBrettanomyces yeast causing spoilage in wine. This research firstly aimed to determine thedetection thresholds of eight Brett-related spoilage compounds in wine. The second aim was todetermine the sensory effect of the four most important Brett-related compounds when presentindividually in wine. The third aim was to determine the sensory effects of these four compoundswhen present in wine in a range of combinations, and to further investigate their effect onconsumer liking. Finally, this project aimed to investigate the incidence of these compounds in asmall range of South African wines.The sensory detection thresholds of 4-ethylphenol, 4-ethylguaiacol, 4-ethylcatechol, 4-vinylphenol, 4-vinylguaiacol, isovaleric acid, isobutyric acid and acetic acid were determined.Apart from 4-ethylcatechol, these values generally agreed well with recent literature wherevalues determined in wine are available. However, the discrepancies highlighted the importanceof the effect of the medium (wine) when determining sensory detection thresholds. The use ofthe median as alternative calculation method was also investigated, and it was found that thismethod gives more insightful results than the standard American Society of Testing Materials(ASTM E679-04) method.Four compounds, namely 4-ethylphenol, 4-ethylguaiacol, 4-ethylcatechol and isovaleric acidwere profiled individually in wine using a trained sensory panel. It was found that all fourcompounds caused a suppression of the natural berry-like character in the wine, which induceda sick-sweet character. 4-ethylphenol contributed Elastoplast™ and leather aromas in the wine,both of which are commonly associated with Brettanomyces taint. 4-ethylguaiacol added amedicinal aroma to the wine, and 4-ethylcatechol and isovaleric acid were responsible forsavoury and pungent aromas, respectively.4-ethylphenol, 4-ethylguaiacol, 4-ethylcatechol and isovaleric acid were also profiled incombination according to the central composite design. Several univariate and multivariatemethods were applied to the dataset obtained. PARAFAC, a multiway method not widelyutilized regarding sensory data, was applied to the data, the results of which werecomplementary to those obtained during univariate and multivariate analyses. It was found thatthere is a great deal of interaction between the four compounds profiled in terms of sensoryeffects. The most notable was the Elastoplast™ attribute, the intensity of which was affected byall four compounds. The pungent attribute was also affected by the 4-ethylphenol concentration. Consumer analysis revealed that some of the samples spiked with Brettanomyces-spoilagecompounds were preferred to the unspiked (control sample). However, no further relationshipcould be found between consumer liking and either chemical composition or sensory profile. It istherefore speculated that consumer liking of Brettanomyces infected wine is driven by morecomplex sensory or socio-demographic factors.Finally, the concentration of 4-ethylphenol, 4-ethylguaiacol, 4-ethylcatechol, 4-vinylphenol, 4-vinylguaiacol, isovaleric acid, isobutyric acid and acetic acid was determined in a small set ofSouth African wines, selected to contain a high proportion of wines spoiled by Brettanomyces.Significant correlations were found between 4-ethylphenol and 4-ethylguaiacol, as well as 4-ethylphenol and isovaleric acid. However, no correlation could be found between 4-ethylphenoland 4-ethylcatechol. It is speculated that this lack of relationship is due to the different precursorprofiles present in the analysed wines. This study paved the way for future investigations on thesensory effects of Brettanomyces spoilage in Pinotage red wine.

[发布机构] Stellenbosch University