Browsing by Author "Porter, Tristan Jade"
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- ItemBiochemical characterization and evaluation of the oenological attributes of Lachancea species(Stellenbosch : Stellenbosch University, 2017-12) Porter, Tristan Jade; Setati, Mathabatha Evodia; Divol, Benoit; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology.ENGLISH SUMMARY: Previously thought to be the catalyst for spoilt wine, several non-Saccharomyces yeasts are now commercially available for winemaking. Increasing investigations into this group of microorganisms has emphasized their oenological potential in terms of their contribution to the organoleptic profile of the resulting wines. However, their sub-optimal fermentation performances, force their combined inoculation with the main wine yeast Saccharomyces cerevisiae. Among the non-Saccharomyces yeasts, Lachancea thermotolerans has been reported to bring about an overall improvement in wine acidity through the production of L-lactic acid and reduction of acetic acid as well as increased glycerol and 2-phenylethanol levels, which can impart a sweet taste and flowery aromas to wine, respectively. Its secretion of hydrolytic enzymes of oenological relevance has also been reported. Other species of the Lachancea genus (L. fermentati and L. lanzarotensis) have also been isolated from the fermentation environment, but have not received the same degree of focus as L. thermotolerans. The aim of this study was to investigate the oenological potential of these species, regarding their expression of oenologically relevant enzymes, their fermentation attributes and the expression and location of β-glucosidase during fermentation of synthetic and real grape must (Muscat d’Alexandrie). All the Lachancea spp. illustrated β-glucosidase activity in initial plate screenings, while none exhibited protease or pectinase activities. L. thermotolerans and L. fermentati also displayed higher tolerance to ethanol and SO2 when exposed to varying concentrations of these inhibitory compounds. Higher fermentation performance was demonstrated by L. thermotolerans strains and L. fermentati, which performed much better in Muscat grape juice, and was the only Lachancea spp. to complete the fermentation in monoculture. During these fermentations, all three Lachancea spp. illustrated β-glucosidase activity, where the highest levels were expressed by a L. thermotolerans strain, Y940. Most of the enzyme activity originated from the cell walls of the yeasts, while lower levels were isolated in the intracellular region and none determined to be released into the medium. The mixed culture fermentations resulted in wine products with significantly different chemical compositions compared to the S. cerevisiae fermentation. L. thermotolerans and L. lanzarotensis mixed culture fermentations resulted in similar wines with increased production of common compounds including isoamyl alcohol, butanol and ethyl phenylacetate. L. fermentati seemingly produced wines dissimilar to the other Lachancea spp., producing levels of acetic acid perhaps flagging this species as a potential spoilage microorganism. This study provided novel information on relatively uninvestigated Lachancea spp., where their oenological potential was highlighted by the ability to express β-glucosidase enzymes during fermentations and producing wines significantly different from S.