Karina Toscano Medina

Tandem repeat-tRNA (TRtRNA) PCR method for the molecular typing of non-Saccharomyces subspecies.

There is a worldwide trend to understand the impact of non-Saccharomyces yeast species on the process of winemaking. Although the predominant species at the end of the fermentation is Saccharomyces cerevisiae, several non-Saccharomyces species present during the first days of the process can produce and/or release aromas that improve the bouquet and complexity of the final wine. Since no genomic sequences are available for the predominant non-Saccharomyces species selected from grapes or musts (Hanseniaspora uvarum, Hanseniaspora vineae, Hanseniaspora opuntiae, Metschnikowia pulcherrima, Candida zemplinina), a reproducible PCR method was devised to discriminate strains at the subspecies level. The method combines different oligonucleotides based on tandem repeats with a second oligonucleotide based on a conserved tRNA region, specific for ascomycetes. Tandem repeats are randomly dispersed in all eukaryotic genomes and tRNA genes are conserved and present in several copies in different chromosomes. As an example, the method was applied to discriminate native M. pulcherrima strains but it could be extended to differentiate strains from other non-Saccharomyces species. The biodiversity of species and strains found in the grape ecosystem is a potential source of new enzymes, fungicides and/or novel sustainable methods for biological control of phytopathogens.

Genome Sequence of the Native Apiculate Wine Yeast Hanseniaspora vineae T02/19AF

ABSTRACT The use of novel yeast strains for winemaking improves quality and provides variety including subtle characteristic differences in fine wines. Here we report the first genome of a yeast strain native to Uruguay, Hanseniaspora vineae T02/19AF, which has been shown to positively contribute to aroma and wine quality.

Non-Saccharomyces and Saccharomyces strains co-fermentation increases acetaldehyde accumulation: effect on anthocyanin-derived pigments in Tannat red wines

During fermentation, Saccharomyces cerevisiae releases into the medium secondary metabolic products, such as acetaldehyde, able to react with anthocyanins, producing more stable derived pigments. However, very limited reports are found about non‐Saccharomyces effects on grape fermentation. In this study, six non‐Saccharomyces yeast strains, belonging to the genera Metschnikowia and Hanseniaspora, were screened for their effect on red wine colour and wine‐making capacity under pure culture conditions and mixed with Saccharomyces. An artificial red grape must was prepared, containing a phenolic extract of Tannat grapes that allows monitoring changes of key phenol parameters during fermentation, but without skin solids in the medium. When fermented in pure cultures, S. cerevisiae produced higher concentrations of acetaldehyde and vitisin B (acetaldehyde reaction‐dependent) compared to M. pulcherrima M00/09G, Hanseniaspora guillermondii T06/09G, H. opuntiae T06/01G, H. vineae T02/05F and H. clermontiae (A10/82Fand C10/54F). However, co‐fermentation of H. vineae and H. clermontiae with S. cerevisiae resulted in a significantly higher concentration of acetaldehyde compared with the pure S. cerevisiae control. HPLC–DAD–MS analysis confirmed an increased formation of vitisin B in co‐fermentation treatments when compared to pure Saccharomyces fermentation, suggesting the key role of acetaldehyde. Copyright

An Inverse Halftoning Algorithms Based on Neural Networks and Atomic Functions

Halftoning and inverse halftoning algorithms are very important image processing tools, widely used in the development of digital printers, scanners, steganography and image authentication systems. Because such applications require to obtain high quality gray scale images from its halftone versions, the development of efficient inverse halftoning algorithms, that be able to provide gray scale images with Peak Signal to Noise Ratio (PSNR) higher than 25, have been research topic during the last several years. Although a PSNR of about 25dB may be enough for several applications, exist several other that require higher image quality. To reduce this problem, this paper proposes inverse halftoning algorithms based on Atomic Function and multi-layer perceptron neural network which provides gray scale images with PSNRs higher than 30dB independently of the method used to generate the halftone image.

Effects of Non-Saccharomyces Yeasts on Color, Anthocyanin, and Anthocyanin-Derived Pigments of Tannat Grapes during Fermentation

Phenolic compounds can affect the sensory characteristics of quality wines, yet the chemical modifications induced by yeasts on phenolic compounds have been studied only to a limited extent. Forty-nine non-Saccharomyces yeast strains belonging to different genera were screened for their effects on color and fermentation capability in a synthetic must supplemented with anthocyanins from Tannat grapes. Total anthocyanins, color intensity, hue, and total polyphenol index were significantly affected (p < 0.001) by the different yeasts studied, and the effects on these parameters were highly diverse in the yeasts’ capacity for improving color indexes of the red grape model wines. Six strains belonging to the species Metschnikowia pulcherrima, Hanseniaspora guilliermondii, H. opuntiae, H. vineae, and H. clermontiae were selected to evaluate the production of anthocyanin-derived pigments; significant variations in the production of four compounds were found between them and compared with Saccharomyces cerevisiae. The formation of vitisin A, vitisin B, malvidin-3-glucoside-4-vinylphenol, and malvidin-3-glucoside-4-vinylguaiacol are reported for the first time for species of genera Hanseniaspora and Metschnikowia.