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Stellenbosch, South Africa

Mtshali P.S.,Stellenbosch University | Divol B.,Stellenbosch University | Van Rensburg P.,Stellenbosch University | Van Rensburg P.,Distell Ltd | Du Toit M.,Stellenbosch University
Journal of Applied Microbiology | Year: 2010

Aims: The objective of this study was to investigate the presence of genes coding for enzymes of oenological relevance in wine Lactobacillus strains isolated from South African grape and wine samples during the 2001 and 2002 harvest seasons. Methods and Results: A total of 120 wine lactobacilli isolates belonging to Lactobacillus plantarum, Lactobacillus hilgardii, Lactobacillus brevis, Lactobacillus pentosus, Lactobacillus paracasei, Lactobacillus sakei and Lactobacillus paraplantarum were genetically screened for enzyme-encoding genes using PCR with primers specific for β-glucosidase, protease, esterase, citrate lyase and phenolic acid decarboxylase. The results of PCR screening showed that the Lactobacillus strains possessed different combinations of enzymes and that some strains did not possess any of the enzymes tested. Confirmation analysis with gene sequencing also showed high similarity of genes with those available in GenBank database. Conclusion: In this study, we have demonstrated the existence of genes coding for wine-related enzymes in wine lactobacilli that could potentially hydrolyse wine precursors to positively influence wine aroma. Significance and Impact of the Study: An expansion of knowledge on the genetic diversity of wine-associated lactic acid bacteria will enable the selection of novel malolactic fermentation starter cultures with desired oenological traits for the improvement of the organoleptic quality of the wine, and hence wine aroma. © 2009 The Authors.

Distell Ltd | Date: 2010-06-22


Louw L.,Stellenbosch University | Louw L.,Distell Ltd | Tredoux A.G.J.,Stellenbosch University | van Rensburg P.,Stellenbosch University | And 4 more authors.
South African Journal of Enology and Viticulture | Year: 2010

The volatile composition of 925 single cultivar young Sauvignon blanc, Chardonnay, Pinotage, Merlot, Shiraz and Cabernet Sauvignon wines of vintages 2005 to 2007, was determined using gas chromatography-flame ionisation detection. Compositional data were compared to published data on young wines from South Africa and other countries. South African young wines analysed in this study had a largely similar volatile composition to that reported in the literature. Significant between-vintage and between-cultivar differences were observed in the volatile composition of the wines investigated in this study. The concentration ranges of four compounds in red wines, hexanol, propanol, diethyl succinate and ethyl lactate, and four compounds in white wines, 2-phenylethanol, hexanoic acid, isoamyl acetate and propanol, were not influenced by vintage effects. This finding was interpreted as the first indication that typical concentration ranges for some aroma compounds can be established for South African young cultivar wines. A trend was observed in the white wines that the alcohols and their respective acetate esters, as well as fatty acids and their ethyl esters, were responsible for the vintage-related effects. Differences in volatile composition between Chardonnay and Sauvignon blanc wines could also largely be explained on the same basis. Classification models were established to discriminate between individual red wine cultivars and between the two white wine cultivars and correct classification rates of respectively, 79 % and 85 % were achieved.

Louw L.,Stellenbosch University | Louw L.,Distell Ltd | Malherbe S.,Distell Ltd | Naes T.,430 As | And 6 more authors.
Food Quality and Preference | Year: 2013

Rapid descriptive sensory profiling methods are under active exploration in the field of sensory science. Methods such as projective mapping, sorting and Napping® are considered time and cost-effective alternatives to conventional descriptive profiling for generating sensory product maps. In this study, the feasibility of applying rapid sensory profiling methods to the sensory evaluation of high alcohol products was challenged based on the considerable sensory fatigue expected due to high alcohol content (38-43% a/v) and perceived sensory complexity. Napping® and partial napping was compared to conventional profiling on a small sample set of six brandies to test the basic validity of these methods. The effect of an increase in sample size on reliability, repeatability and reproducibility was also tested. The results showed that Napping® and partial napping are equally reliable for the evaluation of small sample sets (n=6) of brandy. However, partial napping was shown to be more stable with an increase in sample set size (n=10). The effect of replication and training on reliable Napping® results is also discussed. © 2013 Elsevier Ltd.

Louw L.,Stellenbosch University | Louw L.,Distell Ltd | Oelofse S.,Distell Ltd | Naes T.,430 As | And 6 more authors.
Food Quality and Preference | Year: 2014

Projective mapping has been validated as a practical tool for the rapid sensory profiling of brandy products, although repeatability concerns necessitate repeated measurements in larger sample sets. The reason for poor repeatability could be linked to the complexity of the product type, as well as the physical and possibly psychological factors associated with its high alcohol content. To date no information has been published that tested the effect of these specific factors on panellist performance in projective mapping tasks. This study tested the effect of sample complexity and alcohol content on sensory panel repeatability and accuracy in projective mapping, using six types of commercial alcoholic beverages. In a second objective, the study also tested the effect of prior knowledge of alcohol content of a given product set on panellist performance in projective mapping. The results showed that complexity had the biggest impact on panel performance, while alcohol content had a secondary but decisive influence, largely due to its chemosensory fatiguing nature. Knowledge of the product alcohol content appeared to affect individuals differently, and also had an effect on the terminology used by the panellists to describe the products. The study also introduces the Relative Performance Indicator (RPI) as a new panel performance monitoring tool for projective mapping. © 2013 Elsevier Ltd.

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