Astringency sensation is due to interactions between salivary proteins and phenols and is based on an increased-friction mechanism. Modifications to the profile of salivary proteins and their concentration could affect tannin/protein reactions and hence the intensity of perceived astringency. Salivary characteristics of 65 subjects were compared after abstention from phenol-containing food and immediately after ingestion of tannic acid. The effect of stimulation on saliva characteristics was expressed in terms of D value, computed as the arithmetic difference between values found in saliva samples from the 2 conditions. Based on D values, subjects were clustered in two groups. Cluster 1 (Cl1, 53 cases) was characterized by low D values thus indicating that the basal saliva condition was quickly restored in these subjects. Cluster 2 (Cl2) was composed of 12 subjects whose basal salivary condition was not quickly restored, particularly in terms of salivary protein concentration and profile and saliva haze-forming capacity. Sensory data showed that subjects capable of maintaining constant saliva characteristics were less sensitive to astringent stimuli than subjects in which the same stimulations induced significant saliva modifications. The results suggest that a large proportion of the population are able to maintain their salivary protein concentration and simultaneously intercept and inactivate dietary tannins.

Seven spontaneous Saccharomyces cerevisiae mutants that express dominant resistance to 5,5,5-trifluoro-DL-leucine have been characterised at the molecular level. The gene responsible for the resistance was cloned from one of the mutants (FSC2.4). Determination of its nucleotide sequence showed that it was an allele of LEU4 (LEU4-1), the gene that encodes alpha-isopropyl malate synthase I (alpha-IPM synthase I), and that the mutation involved a codon deletion localised close to the 3' end of the LEU4 ORF. Six different point mutations--four transitions and two transversions--were found in the remaining mutants. Alpha-IPM synthase activity was found to be insensitive to feedback inhibition by leucine in five of the strains. In the other two the enzyme was resistant to Zn2+-mediated inactivation by Coenzyme A, a previously postulated control mechanism in energy metabolism; as far as we know, this represents the first direct in vivo evidence for this mechanism. The seven mutations define a region, the R-region, involved in both leucine feedback inhibition and in Zn2+-mediated inactivation by CoA. Deletion experiments involving the R-region showed that it is also necessary for enzyme activity.

During the course of this study, a new, rapid and reproducible method to assay beta-glucosidase activity was developed. The fact that Saccharomyces and non-Saccharomyces yeast strains are able to express beta-glucosidase activity during the alcoholic fermentation sheds new light on the contribution of these yeasts in the aroma expression of wines.

The present study was undertaken to evaluate the influence of medium pH and inoculation time on the growth and malolactic activity of an Oenococcus oeni culture. Samples of a commercial white grape juice adjusted to pH 3.2, 3.4 or 3.6, and inoculated with Saccharomyces cerevisiae strain CY3079, were inoculated with a malolactic culture (Oenococcus oeni strain 31) at the beginning, middle, and end of alcoholic fermentation. The results obtained from this single case study show that it is possible to inoculate the bacterial culture at the three different times during alcoholic fermentation without slowing down or stopping alcoholic fermentation or causing failure of MLF. However, pH and timing of bacterial inoculation were critical to how rapidly MLF starts. At pH 3.2 a lowering of bacterial viability was observed, but a more important reduction was recorded at all tested pH levels when the bacteria were inoculated halfway through alcoholic fermentation. When inoculation was carried out at the end of alcoholic fermentation, the presence of yeast seemed to favour bacterial viability and activity and bacteria performed MLF even in difficult conditions such as pH values around 3. In all wines malolactic fermentation was accompanied by total degradation of malic and citric acids and production of L-lactic acid, D-lactic and acetic acids. AbbreviationsAF alcoholic fermentation; MLF malolactic fermentation; MRS de Man, Rogosa and Sharpe; YM yeast and mould

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