Characterisation, evaluation and use of non-Saccharomyces yeast strains isolated from vineyards and must

[摘要] ENGLISH ABSTRACT:Wine is the product of a complex biological and biochemical interaction betweengrapes and different microorganisms (fungi, yeasts, lactic acid bacteria and aceticacid bacteria, as well as the mycoviruses and bacteriophages affecting them) inwhich yeasts play the most important role regarding the alcoholic (primary)fermentation. These wine-associated yeasts can be divided into Saccharomyces andnon-Saccharomyces yeasts. During fermentation, there is a sequence of dominanceby the various non-Saccharomyces yeasts, followed by Saccharomyces cerevisiae,which then completes the fermentation. This is especially evident in spontaneouslyfermenting must, which has a low initial S. cerevisiae concentration. Some non-Saccharomyces yeasts can also be found throughout the fermentation. The non-Saccharomyces presence in the fermentation can affect wine quality, either positivelyor negatively. A positive contribution could be especially useful to improve winesproduced from grape varieties with a neutral flavour profile due to non-optimalclimatic conditions and/or soil types. As part of a comprehensive South Africanresearch programme, the specific objectives of this study were: the isolation ofindigenous non-Saccharomyces yeasts from vineyards and musts; the identificationof these isolates; the characterisation and evaluation of predominant species underwinemaking conditions; and the development of a protocol for their use in enhancingwine quality.Initially, 720 isolates representing 24 different species, were isolated from grape(vineyard) and must samples taken over three vintages from four distinctly differentwine producing regions. The isolates were characterised and grouped utilisingbiochemical profiles and DNA karyotyping, whereupon representative isolates wereidentified. The yeast species that had the highest incidence of predominance in thevineyard was Kloeckera apiculafa. However, some vineyard samples werecharacterised by low numbers or absence of this yeast, which is not according togenerally accepted norms. Other species that also predominated in a few of thevineyard samples were Candida pulcherrima, Kluyveromyces thermofolerans,Rhodotorula sp. and Zygosaccharomyces bailii. Generally, there was a greaterdiversity of yeasts in the processed must than from the vineyard samples.Furthermore, while each sample showed a different yeast population, no patternlinking species to climatic zone was observed.Four species i.e. Candida collieulosa, Candida pulcherrima, Candida stel/ata andKloeckera apiculata, were found to predominate in grape must samples.Representative strains consequently received further attention during laboratory andsmall-scale winemaking trials. A protocol was developed whereby individual speciescould be used in co-inoculated fermentations with S. cerevisiae in the small-scaleproduction of wine. An improvement in wine quality was achieved and it was foundthat there was a link between specific species and grape cultivar. The ability ofC. pulcherrima to improve Chenin blanc wine quality was investigated further. Resultsover three vintages showed that the wine produced by the co-inoculated fermentationwas superior to that of a reference wine (produced by S. cerevisiae only). Theimprovement in wine quality was not linked to increased ester content nor were thestandard chemical analyses adversely affected. The effects of pH and wineproduction parameters i.e. 802, fermentation temperature and use of di-ammoniumphosphate (DAP), on this yeast followed the same pattern as that known forS. cerevisiae. This study was successfully completed and the developed protocol canbe used for the improvement of Chenin blanc wine where additional aroma andquality is needed.

[发布机构] Stellenbosch University