Elisa Longo

Production of higher alcohols, ethyl acetate, acetaldehyde and other compounds by 14Saccharomyces cerevisiae wine strains isolated from the same region (Salnés, N.W. Spain)

Fourteen strains of the yeastSaccharomyces cerevisiae were isolated from three wineries in the Salnés wine region (N.W. Spain) at the three different periods of the natural fermentation. Each wild yeast was screened for production of acetaldehyde, ethyl acetate, isobutanol,n-propanol, amylic alcohol and other important enological compounds during laboratory scale fermentations of grape juice. After 25 days at 20°C, the analytical results evidenced variations in the production of acetaldehyde (from 13.1 to 24.3 mg/l), isobutanol (from 27.7 to 51.1 mg/l), amyl alcohols (from 111 to 183 mg/l) and ethyl acetate (from 19.3 to 43.7 mg/l). Although isolated from the same wine region, differences in the wine composition were observed depending on the particular yeast strain used for the vinification experiments.

Improvement of the alcoholic fermentation of grape juice with mixed cultures of Saccharomyces cerevisiae wild strains. Negative effect of Kloeckera apiculata

Four assays were designed to study the fermentative behaviour of two selected wild strains of Saccharomyces cerevislae when inoculated in sterilized grape juice either alone or in association. In addition, a wild strain of Kloeckera apiculata was employed for studying and characterizing the influence of this micro-organism on the fermentations when associated with Sacch. cerevisiae. Fermentation was improved when the two strains of Sacch. cerevisiae were grown together since the residual sugar fell to 0.12% and ethanol increased up to more than 11% (v/v). In this case, a proliferation of the two strains with successive exponential phases was observed. On the other hand, when Kloeckera apiculata was incorporated into the fermentations, these were incomplete with a residual sugar level of 1.64% and a final ethanol concentration of 6.4%.

Role of killer character in spontaneous fermentations from NW Spain: ecology, distribution and significance

SummaryThe presence of killer, resistant and sensitive populations of Saccharomyces cerevisiae along the successive stages of alcoholic fermentation in three vineyards from NW Spain was investigated. The global results showed that approximately 71% were killer-sensitive strains, 6.6% were killer-resistant, and 22.4% belonged to the k2 killer type. However, there were important differences concerning the presence of the three phenotypes during successive stages of fermentation. Killer populations were isolated at the highest percentages in samples from must and from active alcoholic fermentations. Killer-resistant strains steadily increased during fermentation. Additionally, important differences in these populations were observed among the three vineyards. In this sense, the presence of killer populations was more important in samples from the vineyards with higher average pH values of the must. However, great differences in the distribution of killer phenotype between successive vintages (with the same initial pH of must) belonging to the same vineyard implies the presence of other factors effecting killer behaviour.

Effect of L-malate, D-glucose and L-lactate on malolactic fermentation and growth of Lactobacillus plantarum and Lactobacillus curvatus wild strains isolated from wine

Abstract l -Malate fermentative rate in Lactobacillus plantarum and Lactobacillus curvatus was improved when l -malate was over 0.1% but decreased when exogenous d -glucose raised over 0.3% or in the presence of exogenous l -lactate. Significant increases in the growth were observed in the presence of exogenous d -glucose. l -malate residual concentrations were in all cases below 1%.

Mutagenicity test using Vibrio harveyi in the assesment of water quality from mussel farms

This work analyses the mutagenicity of seawater from mussel farms using the Vibrio harveyi mutagenicity test and its relationship with the accumulated pollutants and the development of gonadal neoplasia in mussels. Histological disorders identified as germinoma were observed in the gonad of Mytilus galloprovincialis during the period of study. The prevalence of this pathology is significantly correlated with certain levels of pollutants accumulated in mussels, mainly of PAHs and PCBs, whose toxic equivalents were calculated as EROD induction equivalency. The mutagenicity and toxicity of the water surrounding mussels farms is clearly correlated with the pollutants accumulated and with the neoplasia prevalence in mussels. Such correlations are corroborated by a multivariate analysis. Our results conclude with the utility of V. harveyi test as an optimal and rapid method in the monitoring of the quality of the water from mussel farms and as a tool to control the risks of pollution on mussel production and its safety for human food.

Microbiology of Grape Surfaces and its Importance for Wine Quality

Although humankind has been involved in winemaking since the very beginning of civilization, it was not until the second half of the last century that Pasteur (1857) demonstrated the microbial origin of spontaneous fermentations. Years later, Hansen (1903) established the taxonomic basis for a rational approach to the study of yeasts associated with grapes and to those actually involved in the fermentation process. By the middle of the present century studies in microbial ecology have shown that the vinification process involves a sequential proliferation of different types of yeast and bacteria coming either from the vineyard itself or from the cellar (Mrak and McClung, 1940; Castelli, 1954 and Galzy, 1958)

Characterization of killer-resistant strains of Saccharomyces cerevisiae isolated from spontaneous fermentations

A study of 26 killer-resistant wine strains of Saccharomyces cerevisiae, isolated during spontaneous fermentations in three vineyards in NW Spain, was carried out employing several methods that included a spheroplast-killing assay and analysis of chromosomal DNA patterns by pulse-field agarose electrophoresis. The results showed that 92% of the strains were derivatives of K2 killer toxin producing wine strains isolated from the same fermentations, and that they could be grouped into four different karyotypes. The remaining strains were killer-resistant at cell-wall level and were not related to the others, as was demonstrated by the absence of L and M ds-RNAs and by their different karyotypes.

Influence of the curing of the killer phenotype inSaccharomyces cerevisiae wine strains on their fermentative behaviour

Fermentative behaviour and cell growth have been studied in grape juice inoculated either with two killerSaccharomyces cerevisiae wild strains or with their Acridine Orange-cured isogenic counterparts. The number of viable cells/ml at the beginning of the fermentation, as well as during exponential growth, were higher in grape juices inoculated with the cured strains. The CO2 production, fermentative rate and ethanol and acetic acid production were also higher in the cured strains, particularly during the stage of active fermentation. These differences, however, were minimal at the end of the fermentations.

Effect of different physico-chemical conditions on malolactic fermentation of fourLactobacillus plantarum wild strains isolated from wines of northwestern Spain

SummaryFour strains ofLactobacillus plantarum, were tested for malolactic fermentation under conditions of variations in temperature, pH and SO2, L-malate and ethanol levels. When the pH value was below 3.5, malolactic fermentation was lower and was more sensitive to temperature changes. Malolactic fermentation decreased when the SO2 and ethanol levels were increased. The effects of L-malate levels were not significant.

Improved lysis of wine lactobacilli for high yield isolation and chatacterization of chromosomal DNA

Abstract An improved lysis of Lactobacillus casei and Lactobacillus fermentum wine strains with respect to alternative protocols is described. This lysis protocol yielded 600 to 800 μg of high molecular weight DNA (25–40 kb) per liter of culture. Characterization of the molecular size of Sau 3A-retricted DNA from L . casei , packaging into pBR322 and stable maintenance in E. coli were achieved. This lysis procedure may be an alternative method for the isolation of high molecular DNA from lysis-resistant microorganisms from different environmental sources.