During red wine fermentation, high temperatures may cause stuck fermentation by affecting the physiology of fermenting yeast. This deleterious effect is the result of the complex interaction of temperature with other physicochemical parameters of grape juice, such as sugar and lipid content. The genetic background of fermenting yeast also interacts with this complex matrix and some strains are more resistant to high temperatures than others. Here, the temperature tolerance of nine commercial starters was evaluated, demonstrating that, at high sugar concentrations, half of them are sensitive to temperature. Using a classical backcross approach, one thermo-sensitive commercial starter was genetically improved by introducing quantitative trait loci conferring resistance to temperature. With this breeding program it is possible to obtain a thermo-resistant strain sharing most of its genome with the initial commercial starter. The parental and improved strains were compared for population growth and fermentation ability in various conditions. Despite their common genetic background, these two strains showed slight physiological differences in response to environmental changes that enable identification of the key physiological parameters influencing stuck fermentation.

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Objective: This study aims at examining the patterns of ‘substance’ use in Lebanon among an ’at risk’ population, the university students. Method: A stratified cluster sample of 1,851 students from two major universities was included in the study and the Diagnostic Interview Schedule (version 3) was administered. Results: The prevalence of nicotine users in the sample was 18.3% and of ever consuming alcohol 49.4%. 2.1% of the sample were alcohol abusers and 2.4% alcohol dependents according to DSM-III criteria. For the remaining substances, tranquilizers were found to have the highest rate of ever use (10.2%), whereas heroin had the lowest rate (0.4%); the rates of abuse and dependence in these categories (other than alcohol and nicotine) following DSM-III criteria ranged from 0.1 to 0.8%. Conclusion: University students in Lebanon in this study have relatively low rates of use and abuse of substances but this might be changing.

Background Fermentation completion is a major prerequisite in many industrial processes involving the bakery yeast Saccharomyces cerevisiae. Stuck fermentations can be due to the combination of many environmental stresses. Among them, high temperature and ethanol content are particularly deleterious especially in bioethanol and red wine production. Although the genetic causes of temperature and/or ethanol tolerance were widely investigated in laboratory conditions, few studies investigated natural genetic variations related to stuck fermentations in high gravity matrixes. Results In this study, three QTLs linked to stuck fermentation in winemaking conditions were identified by using a selective genotyping strategy carried out on a backcrossed population. The precision of mapping allows the identification of two causative genes VHS1 and OYE2 characterized by stop-codon insertion. The phenotypic effect of these allelic variations was validated by Reciprocal Hemyzygous Assay in high gravity fermentations (> 240 g/L of sugar) carried out at high temperatures (> 28 °C). Phenotypes impacted were mostly related to the late stage of alcoholic fermentation during the stationary growth phase of yeast. Conclusions Our findings illustrate the complex genetic determinism of stuck fermentation and open new avenues for better understanding yeast resistance mechanisms involved in high gravity fermentations. Electronic supplementary material The online version of this article (10.1186/s12864-019-5959-8) contains supplementary material, which is available to authorized users.

1 fermentation due to the combined effect of ethanol and temperature; a QTL-2 mapping study. Abstract 6 5Background: Fermentation completion is a major prerequisite in many industrial processes 6 6 involving the bakery yeast Saccharomyces cerevisiae. Stuck fermentations can be due to the 6 7 combination of many environmental stresses. Among them high temperature and ethanol content 6 8 are particularly deleterious especially in bioethanol and red wine production. Although the genetic 6 9 causes of temperature and/or ethanol tolerance were widely investigated in laboratory conditions, 7 0 few studies investigated natural genetic variations related to stuck fermentations in high gravity 7 1 matrixes. 2Results: In this study, three QTLs linked to stuck fermentation in winemaking conditions were 7 3 identified by using a selective genotyping strategy carried out on a backcrossed population. The 7 4 precision of mapping allows the identification of two causative genes VHS1 and OYE2 characterized 7 5 by stop-codon insertion. The phenotypic effect of these allelic variations was validated by Reciprocal 7 6Hemyzygous Assay in high gravity fermentations (>240 g/L of sugar) carried out at high 7 7temperatures (>28°C). Phenotypes impacted were related to the late stage of alcoholic fermentation 7 8 during the stationary growth phase of yeast. 7 9 Conclusions: The genes identified are related to molecular functions such as Programed Cell 8 0 Death, ROS metabolism and respire-fermentative switch and were never related to fermentation 8 1 efficiency. Our findings open new avenues for better understanding yeast resistance mechanisms 8 2 involved in high gravity fermentations. 8 3 8 4 8 5 3