Using quantitative real-time PCR, the suitability of the HSP30 pr

Using quantitative real-time PCR, the suitability of the HSP30 promoter to specifically drive stationary-phase expression of the native FLO5 and FLO11 ORFs in BM45 and VIN13 transgenic strains under synthetic MS300 wine fermentation conditions has been demonstrated in our recent research study (Govender et al.,

2010). In this study, transgenic yeast strains (BM45-F5H, BM45-F11H, VIN13-F5H and VIN13-F11H) in which an ORF of a dominant chromosomal flocculation gene (FLO5 or FLO11) was placed under the transcriptional control of the stationary-phase inducible HSP30 promoter displayed metabolic fermentation profiles in natural Merlot must that were almost indistinguishable from their parental host wine yeast strains. Considering that wines are regarded selleck screening library as dry if their residual sugar content is <5 g L−1, it is clearly evident that Merlot wines (≤1.95 g L−1 residual

sugars) produced by both parental host wine yeast strains and their HSP30p transgenic descendants were fermented almost equally well to dryness. Moreover, HSP30p transgenic wine yeast strains produced Merlot wines that displayed almost identical volatile and aroma compound profiles. Thus, it can be suggested that introduction of promoter replacement cassettes designed for induction of late fermentation flocculation does not compromise the desirable oenological properties of original nonflocculent host wine yeast strains under authentic red wine-making conditions. Thymidine kinase The BM45-F5H and VIN13-F5H transformants displayed almost identical Flo1-type flocculation Tyrosine Kinase Inhibitor Library intensity in both synthetic MS300 and Merlot wine fermentations (Govender et al., 2010). Only

the BM45-F5H strain was capable of generating compacted or ‘caked’ lees fractions, thereby providing a distinct separation of the fermented wine product and lees fractions. The benefit of this attractive property is that it facilitates simpler and faster recovery of wines and it also promotes a greater volume recovery of fermented wine product. This improvement has significant financial cost-saving implications and can be directly attributed to the superior flocculent ability of the BM45-F5H transgenic strain. The BM45-F11H and VIN13-F11H transgenic wine yeast strains yielded strong flocculent phenotypes that displayed a combination of both Ca2+-dependent and Ca2+-independent flocculation characteristics under authentic red wine-making conditions. In addition, no flocculent phenotype was displayed by the same transgenic yeast strains in aerobic shake-flask MS300 batch fermentations supplemented with an individual red wine fermentation component (pectin, potassium bitartrate, diatomaceous earth, gallic acid, caffeic acid, catechin or a tannin). As such, these individual components seem not to aid in the development of the novel FLO11-mediated flocculation phenotype observed under authentic red wine fermentations conditions.

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