Lactic acid production is an important feature of the yeast Lachancea thermotolerans that has gained increasing interest in winemaking. In particular, in light of climate change, the biological acidification and ethanol reduction by the use of selected yeast strains may counteract the effect of global warming in wines. Here, the enological potential of a high lactate-producing L. thermotolerans strain (P-HO1) in mixed fermentations with S. cerevisiae was examined. Among the different inoculation schemes evaluated, the most successful implantation of L. thermotolerans was accomplished by sequential inoculation of S. cerevisiae, i.e., at 1% vol. ethanol. P-HO1produced the highest levels of lactic acid ever recorded in mixed fermentations (10.4 g/L), increasing thereby the acidity and reducing ethanol by 1.6% vol. L. thermotolerans was also associated with increases in ethyl isobutyrate (strawberry aroma), free SO2, organoleptically perceived citric nuances and aftertaste. To start uncovering the molecular mechanisms of lactate biosynthesis in L. thermotolerans, the relative expressions of the three lactate dehydrogenase (LDH) paralogous genes, which encode the key enzyme for lactate biosynthesis, along with the alcohol dehydrogenase paralogs (ADHs) were determined. Present results point to the possible implication of LDH2, but not of other LDH or ADH genes, in the high production of lactic acid in certain strains at the expense of ethanol. Taken together, the important enological features of P-HO1 highlighted here, and potentially of other L. thermotolerans strains, indicate its great importance in modern winemaking, particularly in the light of the upcoming climate change and its consequences in the grape/wine system.
Vineyard- and winery-associated lactic acid bacteria (LAB) from two major PDO regions in Greece, Peza and Nemea, were surveyed. LAB were isolated from grapes, fermenting musts, and winery tanks performing spontaneous malolactic fermentations (MLF). Higher population density and species richness were detected in Nemea than in Peza vineyards and on grapes than in fermenting musts. Pediococcus pentosaceus and Lactobacillus graminis were the most abundant LAB on grapes, while Lactobacillus plantarum dominated in fermenting musts from both regions. No particular structure of Lactobacillus plantarum populations according to the region of origin was observed, and strain distribution seems random. LAB species diversity in winery tanks differed significantly from that in vineyard samples, consisting principally of Oenococcus oeni. Different strains were analysed as per their enological characteristics and the ability to produce biogenic amines (BAs). Winery-associated species showed higher resistance to low pH, ethanol, SO2, and CuSO4 than vineyard-associated isolates. The frequency of BA-producing strains was relatively low but not negligible, considering that certain winery-associated Lactobacillus hilgardii strains were able to produce BAs. Present results show the necessity of controlling the MLF by selected starters in order to avoid BA accumulation in wine.
Two bacterial strains (B18BM42 T and B18NM6) were recovered during a study of bacterial diversity on wine grapes (Vitis vinifera L.) from the Nemea region in Greece. Phylogenetic analysis based on 16S rRNA gene sequences placed the two strains within the genus Weissella, and found them to be most closely related to Weissella minor NRIC 1625 T followed by Weissella viridescens NRIC 1536 T (99.1 and 98.9 % sequence similarity, respectively). The level of DNA-DNA relatedness between strains B18NM42 T and W. minor NRIC 1625 T or W. viridescens NRIC 1536 T was 31.9 and 35.0 %, respectively. The two novel strains could be genetically differentiated from their closest relatives by REA-PFGE (restriction enzyme analysis-pulse field gel electrophoresis), RAPD (randomly amplified polymorphic DNA) and rep-PC R analyses (repetitive sequence-based PCR). Physiological examination showed that the novel strains can be distinguished from phylogenetically related species by their ability to grow at 42 6C and by certain carbohydrate fermentations. Based on the evidence above, the affiliation of the two strains to a novel species with the proposed name Weissella uvarum sp. nov. is suggested. The type strain is B18NM42 T (5DSM 28060 T 5NCCB 100484 T ).
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