Characterization of palm wine yeasts using osmotic, ethanol tolerance and the isozyme polymorphism of alcohol dehydrogenase

Physiologic characteristics of ten palm-wine yeast isolates obtained from nine localities in four provinces in southern Cameroon were assessed using sensitivity to chloramphenicol, tolerance to acetic acid, ethanol tolerance, osmotolerance as well as protein and alcohol dehydrogenase (ADH) polymorphism. None of these isolates was sensitive to 30 ìg/ml chloramphenicol and all were nontolerant to 1% acetic acid. Some of the isolates (Vip 2 and Vip 10) showed tolerance to both high sucrose and ethanol concentrations, criteria which are useful in fermentation. Results indicated that 80% of the strains were able to grow at 15% alcohol solution and only 20% grew on 40% sucrose solution. The denatured protein pattern (SDS-PAGE) as well as the native protein pattern was similar for all strains. The ADH pattern showed a high diversity based on which isolates were differentiated into three patterns. The electrophoretic patterns showed that the ADH pattern was the best criterion for diversity characterisation because of its specificity and variability

Les microorganismes genetiquement modifies: potentiel et risques pour l\'environment d\'un pays Africain en developpement

No Abstract.Journal of the Cameroon Academy of Sciences Vol. 7 (3) 2008: pp. 149-15

Optimisation de la production d'éthanol par les techniques d'hydrolyse de l'amidon de manioc et la fermentation de la levure de bière (Saccharomyces cerevisiae)

Nous avons évalué les paramètres optimum pour la production d'alcool à partir de l'efficacité d'hydrolyse de l'amidon: chimique (HCl), enzymatique (amylase de Aspergillus niger ou de malt) et mixte (chimique et enzymatique). La fermentation alcoolique par la levure de bière est suivie, à travers l'influence du pH, de la température, du substrat et de la durée. La méthode la plus efficace est l'hydrolyse mixte avec 82% à 86% de rendement et la moins efficace est l'hydrolyse chimique avec 31% de rendement. La teneur en alcool augmente avec la concentration en substrat jusqu'à un optimum à 200 g/l. Le rendement le plus élevé pour la production d'alcool est 47,9%. Les conditions les plus favorables sont: 50 g/l de sucre, pH de 6, 30oC et 36 h de fermentation pour une meilleurerentabilité. On peut optimiser ces résultats en utilisant des technologies plus efficaces pour l'hydrolyse de l'amidon. Il vaut mieux produire l'éthanol à partir d'une fermentation contrôlée pour éviter les intoxications provoquées par le méthanol.Mots clés: fermentation alcoolique, Saccharomyces cerevisiae, amidon de manioc, Aspergillus niger, malt, amylases.Optimum parameters suitable for alcohol production were set up. We tested the efficiency of starch hydrolysis using three methods: hydrochloric acid; enzymatic using microbial Aspergillus niger amylases or malt amylases, mixed hydrolysis combining chemical and enzymatic methods. Alcoholic fermentation was assessed using yeast and wort hydrolysis of starch. The pH, temperature, substrate content and duration of the fermentation were studied. The most efficient method is the mixed chemical and enzymatic hydrolysis because it yielded 82 to 86% and the least efficient is chemical hydrolysis which yielded 31% compared to glucose fermentation. Alcohol concentration increased with substrate concentration to an optimum at 200 g/l. The highest alcohol yield was 47.9%. The optimum parameters for alcohol production using yeast were: 150 g/l, pH of 6, 30oC and duration of 36 h for the best profitability. These results could be improved by using more efficient technology for starch hydrolysis and alcohol production through high ethanol and substrate tolerance. The production of ethanol using established technology is recommended in order to avoid methanol intoxication from uncontrolled fermentation.Key words: alcoholic fermentation, Saccharomyces cerevisiae, cassava starch, Aspergillus niger, malt, amylases