No abstract

Extending the time before harvest-and therefore increasing grape maturity-enhances ripe fruit wine flavours and wine colour intensity, and also decreases unripe green and vegetal wine flavours. Greater maturity, however, increases sugar concentration, which in turn leads to wines with elevated ethanol concentration. High ethanol concentration can reduce the complexity of a wine by suppressing aroma intensity, while also increasing the perception of 'hotness' and 'bitterness'. In addition, health and economic considerations combined with market demand have the wine industry actively seeking ways to facilitate the production of wines with lower alcohol concentration. This review summarises the latest research aimed at reducing wine alcohol concentration, including viticultural practices, pre-fermentation and winemaking practices, microbiological strategies, and post-fermentation approaches and processing technologies. The effect of these practices on wine flavour is also discussed.

ABSTRACTSaccharomyces cerevisiaehas evolved a highly efficient strategy for energy generation which maximizes ATP energy production from sugar. This adaptation enables efficient energy generation under anaerobic conditions and limits competition from other microorganisms by producing toxic metabolites, such as ethanol and CO2. Yeast fermentative and flavor capacity forms the biotechnological basis of a wide range of alcohol-containing beverages. Largely as a result of consumer demand for improved flavor, the alcohol content of some beverages like wine has increased. However, a global trend has recently emerged toward lowering the ethanol content of alcoholic beverages. One option for decreasing ethanol concentration is to use yeast strains able to divert some carbon away from ethanol production. In the case of wine, we have generated and evaluated a large number of gene modifications that were predicted, or known, to impact ethanol formation. Using the same yeast genetic background, 41 modifications were assessed. Enhancing glycerol production by increasing expression of the glyceraldehyde-3-phosphate dehydrogenase gene,GPD1, was the most efficient strategy to lower ethanol concentration. However, additional modifications were needed to avoid negatively affecting wine quality. Two strains carrying several stable, chromosomally integrated modifications showed significantly lower ethanol production in fermenting grape juice. Strain AWRI2531 was able to decrease ethanol concentrations from 15.6% (vol/vol) to 13.2% (vol/vol), whereas AWRI2532 lowered ethanol content from 15.6% (vol/vol) to 12% (vol/vol) in both Chardonnay and Cabernet Sauvignon juices. Both strains, however, produced high concentrations of acetaldehyde and acetoin, which negatively affect wine flavor. Further modifications of these strains allowed reduction of these metabolites.

Adaptive evolution of microorganisms has largely been used to study evolutionary responses to various environmental factors, as well as to create new strains for industrial applications. Although new industrial strains can be constructed using recombinant DNA technologies, consumer concerns about genetically modified (GM) organisms limit their use, particularly in food and beverage production. We have applied adaptive evolution with sulfite at alkaline pH as a selective agent to generate a stable mutant of Saccharomyces cerevisiae with enhanced glycerol production; a desirable characteristic in wine production. The mutant produces 41% more glycerol and has enhanced sulfite tolerance compared to the parental strain it was derived from. Backcrossing to produce heterozygous diploids revealed that the high-glycerol phenotype is recessive, while tolerance to sulfite was partially dominant, and these traits, at least in part, segregate from each other. This work demonstrates the potential of adaptive evolution for development of novel non-GM yeast strains with desirable phenotypes, and highlights the complexity of adaptive responses to sulfite selection. 01-3: Genetic diversity of indigenous Saccharomyces cerevisiae from sugar mills in São Paulo state, Brazil Brazil is the biggest world producer of bioethanol from sugar cane which is a promising alternative for fossil fuel consumption. Although many sugar mills currently start fermentation process by inoculating selected Saccharomyces cerevisiae commercial strains (BG-1, CAT-1, PE-2, SA-1), wild yeast strains appear because of its unsterile condition. This work aimed to study the genetic diversity of these indigenous S. cerevisiae for the first time in Brazil using microsatellite. Yeast samples (175) were collected at several plants located in São Paulo state (Araras, Avaré, Jaboticabal, Pirassununga and São Manuel) during 2008, 2009 and 2010 harvest seasons. Ninety one strains were S. cerevisiae confirmed by rRNA ITS region amplification and they were tested by 3 microsatellite markers in order to differentiate wild yeasts from the selected ones. Thirty-five indigenous S. cerevisiae strains with a unique pattern were tested by other 6 microsatellite loci. All these 9 loci amplifications were used to build a phylogenetic tree showing high genetic diversity distributed in two main groups. The commercial strains BG-1, CAT-1 and SA-1 were arranged together in one group but PE-2 was isolated. The wild strains were related according to geographic origin and season. The high diversity showed in this work opens a new perspective in bioprospecting of more efficient strains to produce ethanol.