Influence of Glutathione on Yeast Fermentation Efficiency under Copper Stress.

Copper in grape musts can influence the fermentation efficiency of Saccharomyces cerevisiae during winemaking. The present study revealed the impact of glutathione addition on yeast strains with variable copper sensitivity. The antioxidant glutathione increased yeast vitality and fastened sugar metabolism at copper concentrations up to 0.39 mM. A significant accumulation of acetaldehyde at high copper concentrations was mitigated by the addition of 20 mg L-1 glutathione. Low recovery of glutathione added implicated a complexation of both compounds. Specific alcohol dehydrogenase (ADH) activity was inhibited or reduced in the enzyme extracts of the copper-stressed yeast cells. The activity was restored in fermentations with glutathione at a copper concentration of 0.16 mM. At low copper concentrations, glutathione decreased ADH activity presumably due to complexation of essential copper amounts. Results provide important information on the use of glutathione as an antioxidant in winemaking to counteract negative effects of copper-rich musts on copper-sensitive yeast strains.

Oxidation of Wine Polyphenols by Secretomes of Wild Botrytis cinerea Strains from White and Red Grape Varieties and Determination of Their Specific Laccase Activity.

Processing of Botrytis cinerea-infected grapes leads to enhanced enzymatic browning reactions mainly caused by the enzyme laccase which is able to oxidize a wide range of phenolic compounds. The extent of color deterioration depends on the activity of the enzymes secreted by the fungus. The present study revealed significant differences in the oxidative properties of secretomes of several B. cinerea strains isolated from five grape varieties. The presumed laccase-containing secretomes varied in their catalytic activity toward six phenolic compounds present in grapes. All strains led to identical product profiles for five of six substrates, but two strains showed deviating product profiles during gallic acid oxidation. Fast oxidation of caffeic acid, ferulic acid, and malvidin 3-O-glucoside was observed. Product formation rates and relative product concentrations were determined. The results reflect the wide range of enzyme activity and the corresponding different impact on color deterioration by B. cinerea.

Growth suppression of Fusarium culmorum, Fusarium poae and Fusarium graminearum by 5-n-alk(en)ylresorcinols from wheat and rye bran.

Alk(en)ylresorcinols (AR), a class of phenolic lipids, are regarded as antifungal compounds showing high potential for the use in plant protection, especially against Fusarium head blight (FHB). In view of the very limited knowledge of the activity of single AR against Fusarium species, the antifungal effect of crude extracts, fractions and isolated homologues from wheat and rye bran was determined. It was shown that the saturated AR are the active compounds in the extracts, whereas the presence of unsaturated molecules leads to an antagonistic effect. The activity of single saturated AR is dependent on the chain length, but for highest antifungal efficiency a mixture of saturated homologues is required. Affecting the stage of germination, these molecules reduce, and may even completely prevent, the growth of the tested Fusarium species.