María José García

Comparative physiology of salt tolerance in Candida tropicalis and Saccharomyces cerevisiae

The salt tolerance of the respiratory yeast Candida tropicalis and the fermentative yeast Saccharomyces cerevisiae have been compared in glucose media. C. tropicalis showed a better adaptation to Na+ and Li+ and maintained higher intracellular K+:Na+ and K+:Li+ ratios than S. cerevisiae. However, C. tropicalis showed a poorer adaptation to osmotic stress (produced by KCl and sorbitol) and exhibited reduced glycerol production as compared to S. cerevisiae. In media with the non-repressing sugar galactose as carbon source, S. cerevisiae exhibited reduced glycerol production and increased sensitivity to osmotic stress. Under these conditions, S. cerevisiae, but not C. tropicalis, utilized trehalose as a more important osmolyte than glycerol. These results suggest that the relative tolerance of yeast to the osmotic and cation toxicities of NaCl, and the underlying relative capabilities for osmolyte synthesis and cation transport, are modulated by the general catabolite control exerted by glucose.

Application of Multivariate Regression Methods to Predict Sensory Quality of Red Wines

Several multivariate methods including partial least squares (PLS) regression, principal component regression (PCR) or multiple linear regression (MLR) have been applied to predict wine quality, based on the definition of chemical and phenolic parameters of grapes and wines harvested at different ripening levels. Three different models including grape phenolic maturity parameters (grape), wine phenolic parameters (wine) and a combination of grape and wine phenolic parameters (grape + wine) were analysed for each of the wine sensory attributes. The grape parameter model has been presented as the best test to predict wine quality based on sensory scores. On the other hand, wine models showed lower accuracy. The combination of grape and wine parameters presented intermediate results showing sometimes good predictability. Moreover, PLS and PCR appeared as more accurate multivariate methods compared to MLR. Although MLR showed higher correlation coefficients, lower RPD values were observed, displaying thus its lower prediction accuracy. Multivariate calibration statistics appeared as a promising tool to predict wine sensory quality in an easy and inexpensive way.

Nota. Diferenciación de vinos tintos varietales de la Comunidad Valenciana a partir del contenido de alcoholes y polioles / Note. Differentiation of varietal red wines from Communidad Valenciana (Spain) based on their composition in terms of alcohols and polyols:

The composition in terms of alcohols and polyols of 44 and 49 red wines (harvested in 1994 and 1995, respectively) produced in Comunidad Valenciana (Spain) from the grape varieties Cabernet Sauvignon, Tempranillo, Monastrell and Bobal was,analyzed. Discriminant analysis revealed differences among wines, and a clear separation of the samples (90 and 98%) was obtained. The most important compo nents in the differentation of the varieties studied were isoamyl alcohol for Cabernet Sauvignon, cis- 3-hexenol and isobutyl alcohol for Tempranillo, methanol and cis-3-hexenol for Monastrell, and 2,3- butanediol for Bobal. The classification obtained by elimination of the five less significant variables was similar to the one obtained using statistical treatment of all variables (with 84% and 90% in their respective harvests).

Crucial Reactions for Salt Tolerance in Yeast

Random over-expression of genes in multicopy plasmids and gene disruptions have uncovered rate-limiting steps for salt tolerance in the model organism Saccharomyces cerevisiae (baker’s yeast). In cells growing in glucose media intracellular sodium toxicity is the major component of salt stress. In minimal synthetic media sodium toxicity primarily affects methionine biosynthesis. This is due to sodium inhibition of the 3′,5′-bisphosphate nucleotidase encoded by the HAL2/MET22 gene. The sodium-extrusion ATPase encoded by the ENA1/PMR2 gene is the major determinant of sodium homeostasis, together with its complex regulatory system, which includes the calcineurin and HAL3 (HAL1) pathways.