Ethanol-induced changes in the fatty acid composition of Lactobaci//us hilgardii, its effects on plasma membrane fluidity and relationship with ethanol tolerance

The effect of environmental ethanol concentration on the fatty acid composition of strains of Lactobacillus hilgardii, differing in their tolerance to ethanol, was determined. A marked increase in the proportion of lactobacillic acid (a cyclopropane fatty acid) and a decrease in oleic and vaccenic acids with increasing ethanol concentration was observed. The amount of lactobacillic acid determined at standard conditions (25°C, 0% ethanol) was found to be proportional to the ethanol tolerance of the strains studied. The effect of this alcohol on plasma membrane fluidity was studied by differential scanning calorimetry. The adaptive response to growth in the presence of high concentrations of ethanol produced membranes which, within the limits of ethanol tolerance, maintained the fluidity and integrity in an environment which tends to increase membrane rigidity. When pre-adapted cells are analysed in the absence of environmental ethanol there is a measurabie increase in fluidity. It is proposed that this phenomenon may be correlated with the increase in the proportion of lactobacillic acid. The existence of a relationship between membrane fluidity and ethanol tolerance is discussed

Use of different nitrogen sources by Saccharomyces cerevisiae during alcoholic fermentation and their impact on aroma profile

I Congreso Nacional de Biotecnología Enológica. Invinotec. Vinomio. León. 26-31 Octubre 2010.Nitrogen is essential for yeast metabolism and growth and is considered to be a limiting factor during the fermentation process. Nitrogen availability and uptake also affects the aromatic profile in wine (Bell & Henschke, 2005). For these reasons, nitrogen requirements of wine yeast during fermentation would be an important control parameter for industrial fermentations. In this work, a new methodology to determine nitrogen requirements of yeast depending on sugar content in must was developed and these results were tested in different fermentation processes.This work was supported by a predoctoral fellowship from JAE Program (CSIC) and the DEMETER project (Ingenio2010-CENIT).Peer reviewe

Effect of pure and mixed cultures of the main wine yeast species on grape must fermentations

10 pages, 2 figures, 3 tables.-- Printed version published June 2010.-- The original publication is available at www.springerlink.comMixed inoculation of non-Saccharomyces yeasts and S. cerevisiae is of interest for the wine industry for technological and sensory reasons. We have analysed how mixed inocula of the main non-Saccharomyces yeasts and S. cerevisiae affect fermentation performance, nitrogen consumption and volatile compound production in a natural Macabeo grape must. Sterile must was fermented in triplicates and under the following six conditions: three pure cultures of S. cerevisiae, Hanseniaspora uvarum and Candida zemplinina and the mixtures of H. uvarum:S. cerevisiae (90:10), C. zemplinina:S. cerevisiae (90:10) and H. uvarum:C. zemplinina:S. cerevisiae (45:45:10). The presence of non-Saccharomyces yeasts slowed down the fermentations and produced higher levels of glycerol and acetic acid. Only the pure H. uvarum fermentations were unable to finish. Mixed fermentations consumed more of the available amino acids and were more complex and thus better able to synthesise volatile compounds. However, the amount of acetic acid was well above the admissible levels and compromises the immediate application of mixed cultures.The present work has been financed by the projects AGL2007-66417-C02-02/ALI and AGL2007-65498-C02-02/ALI of the Spanish Ministry of Education and Science.Peer reviewe

Ann. microbiol.

Purpose Brettanomyces bruxellensis is a serious source of concern for winemakers. The production of volatile phenols by the yeast species confers to wine unpleasant sensory characteristics which are unacceptable by the consumers and inevitably provoke economic loss for the wine industry. This ubiquitous yeast is able to adapt to all winemaking steps and to withstand various environmental conditions. Moreover, the ability of B. bruxellensis to adhere and colonize inert materials can be the cause of the yeast persistence in the cellars and thus recurrent wine spoilage. We therefore investigated the surface properties, biofilm formation capacity, and the factors which may affect the attachment of the yeast cells to surfaces with eight strains representative of the genetic diversity of the species.[br/] Methods The eight strains of B. bruxellensis were isolated from different geographical and industrial fermentation origins. The cells were grown in synthetic YPD medium containing 1% (w/v) yeast extract (Difco Laboratories, Detroit), 2% (w/v) bacto peptone (Difco), and 1% (w/v) glucose. Surface physicochemical properties as electrophoretic mobility and adhesion to hydrocarbon of the cells were studied. The ability of the strains to form biofilm was quantified using a colorimetric microtiter 96-well polystyrene plate. Biochemical characteristics were examined by colorimetric methods as well as by chemical analysis.[br/] Result Our results show that the biofilm formation ability is strain-dependent and suggest a possible link between the physicochemical properties of the studied strains and their corresponding genetic group.[br/] Conclusion The capacity to detect and identify the strains of the spoilage yeast based on their biofilm formation abilities may help to develop more efficient cleaning procedures and preventing methods