Wine aromatic compound production and fermentative behaviour within different non-Saccharomyces species and clones.

AIMS: Twenty-five enological yeasts belonging to nine different species (Candida zeylanoides, Cryptococcus uzbekistanensis, Debaryomyces hansenii, Lachancea thermotolerans, Metschnikowia pulcherrima, Torulaspora delbrueckii, Williopsis pratensis, Zygosaccharomyces bailii and Saccharomyces cerevisiae) were screened for aroma formation and fermentative behaviour as part of a non-Saccharomyces yeast selection programme. METHODS AND RESULTS: Pure cultures were inoculated in pasteurized grape juice in order to perform alcoholic fermentations. Some non-Saccharomyces species did not ferment, others did not get established and none of them completed alcoholic fermentations. The physico-chemical parameters of the wines and the abundance of aromatic compounds at the end of alcoholic fermentation highlighted the notable differences in the aroma-forming ability and fermentative behaviour of the different non-Saccharomyces species, but not within clones. CONCLUSIONS: Lower diversity was detected within non-Saccharomyces species than that reported in S. cerevisiae with regard to enological behaviour and aromatic profiles. Metschnikowia pulcherrima and L. thermotolerans are the two species with higher possibilities to become an inoculum. SIGNIFICANCE AND IMPACT OF THE STUDY: Few significant differences were found within clones of the same species, but very important parameters in wine quality, such as volatile acidity, ethyl acetate and acetoin, which would justify selection programmes within those species. The results also demonstrated that T. delbrueckii and L. thermotolerans are two close species in their aromatic profiles.

Genetic and phenotypic intraspecific variability of non-Saccharomyces yeasts populations from La Rioja winegrowing region (Spain).

AIMS: To determine the intraspecific genetic diversity within five non-Saccharomyces yeast species and the diversity in phenotypic characteristic related to their technological properties. METHODS AND RESULTS: Seventy-one non-Saccharomyces yeasts isolated from different fermentations and facilities of the DOCa Rioja (Spain) belonging to five different wine species (Torulaspora delbrueckii, Lachancea thermotolerans, Metschnikowia pulcherrima, Zygosaccharomyces bailii and Williopsis pratensis) were subjected to clonal characterization by RAPD-PCR, which evidenced wide diversity between them. They were also submitted to a screening for some oenological traits related to the improvement of the aroma of the wine and yeast development in musts. Strains within the same species showed different enzyme activities, tolerated different levels of SO2 and possessed different killer phenotypes. These characteristics made them adjust better or worse to specific vinification processes or wine quality criteria. CONCLUSIONS: A significant genetic and phenotypic variation within the non-Saccharomyces species studied was found, which makes necessary to carry out a selection process in each one. SIGNIFICANCE AND IMPACT OF THE STUDY: Williopsis pratensis, a species that has not been thoroughly explored, may deserve further consideration for oenological applications. Due to the wide range of variation within species, the strains adaptation to the SO2 levels in musts has to be taken into account in selection processes.

Changes on grape phenolic composition induced by grapevine foliar applications of phenylalanine and urea.

Grapevines may require the input of nitrogen to grow and to guarantee an appropriate grape composition. Recently there has been a growing interest in foliar fertilization, which entails a fast and efficient assimilation of the products. The aim of this work was to study the influence of foliar applications of phenylalanine and urea, at two different doses, on grape anthocyanins, flavonols, flavan-3-ols, phenolic acids, and stilbenes. All treatments were applied at veraison and one week later at doses of 0.9 and 1.5 kg N/ha. The results showed that the synthesis of phenolic compounds was favoured by foliar applications of phenylalanine and urea. The application of the lowest dose of urea was the most effective treatment, increasing the content of several anthocyanins and flavonols. Moreover, none of the foliar treatments worsened the grape phenolic composition. In conclusion, foliar application of phenylalanine and especially urea, could be an interesting management tool for improving grape quality and their health-promoting properties.

Study of the effects of proline, phenylalanine, and urea foliar application to Tempranillo vineyards on grape amino acid content. Comparison with commercial nitrogen fertilisers.

The aim of this work was to study the influence of foliar application of different nitrogen sources on grape amino acid content. The nitrogen sources applied to Tempranillo grapevines were proline, phenylalanine, urea, and two commercial nitrogen fertilisers, both without and with amino acids in their formulations. All treatments were applied at veraison and one week later. Proline treatment did not affect the must nitrogen composition. However, phenylalanine and urea foliar application enhanced the plants' synthesis of most of the amino acids, producing similar effects. In addition, the spray of commercial nitrogen fertilisers over leaves also induced a rise in grape amino acid concentrations regardless of the presence or absence of amino acids in their formulation. The most effective treatments were phenylalanine and urea followed by nitrogen fertilisers. This finding is of oenological interest for improved must nitrogen composition, ensuring better fermentation kinetics and most likely enhancing wine quality.