Pilar Blanco

Use of a PGU1 recombinant Saccharomyces cerevisiae strain in oenological fermentations

Aim: The aim of this work was the construction of an oenological Saccharomyces cerevisiae strain able to overexpress the PGU1 gene in order to be used in trial fermentations.

Genetic determination of polygalacturonase production in wild-type and laboratory strains of Saccharomyces cerevisiae

Abstract The genetic determination of polygalacturonase (PG) production in Saccharomyces cerevisiae was studied by biochemical and classical genetic techniques. Crosses of PG+ strains with PG– strains showed that in the haploid wild-type-derived strain, two structural genes were involved in the production of a hydrolysis halo on plates with polygalacturonic acid. However, in the case of PG+ laboratory strain IM1-8b, the phenotype was controlled by only one structural gene although the analysis of PG– IM1-8b mutants demonstrated the existence of at least two complementation groups. All these genetic results were assessed biochemically by means of cation-exchange chromatography. Two enzymes were separated in the wild-type strain, and only one in the laboratory strain. The three enzymes had different Km values, molecular masses, and optimal pHs for activity.

Grape Juice Biodegradation by Polygalacturonases from Saccharomyces cerevisiae

Abstract Some strains of S. cerevisiae capable of degrading pectic susbstances were selected in order to determine their effect on must biodegradation and, in particular, on the clarification processes. The pectolytic activity in these yeasts was always lower than in filamentous fungi and certain bacteria. The effect of pectinases from these three biotic groups, as far as the viscosity was concerned, was not appreciable in either case; however, a relevant effect, caused by enzymes from yeasts, on filtration time was found. With strains 1389 and C6, the filtration time was reduced by about 50%. It is concluded that biodeterioration of must/wine may be caused by an excess of yeast polygalacturonases originating during primary fermentation from the unappropriate S. cerevisiae strain giving rise to thin lines.

Effect of squalene on astaxanthin production by a mutant of Phaffia rhodozyma

The effect of different sesquiterpenes on carotenoid synthesis in Phaffia rhodozyma was studied. Addition of squalene to the culture medium resulted in a decrease in the echinenone and trans-astaxanthin concentrations, whereas β-carotene remained unchanged. The role of squalene as an inhibitor of ketocarotenoid synthesis in Ph. rhodozyma is discussed.

Predominance of malolactic fermentation overd-glucose utilization inLactobacillus plantarum andLactobacillus curvatus wine strains

SummaryTwo selected wine strains of the genusLactobacillus (L. plantarum 197 andL. curvatus 783) were tested for their ability to complete malolactic fermentation (MLF) in a synthetic medium (PBM-broth) supplemented withL-malic acid (7.5–74.6 mM) andD-glucose (5.5–55 mM). The 24 directed fermentation assays, 12 for each bacterial strain, were carried out at 20°C and pH 3.5. MLF was completed (residualL-malic acid ≤0.2 mM) in eight days in 19 of the 24 fermentation assays, even in the presence of 74.6 mML-malic acid or 55.5 mMD-Glucose utilization was generally simultaneous to MLF but was completed (residual concentrations ≤0.2 mM) only in 6 of the 24 fermentation assays. These results support the use of these strains in directed MLF assays at the very differentL-malic acid andD-glucose concentrations tested.