Preliminary Studies on the In Vitro Interactions between the Secondary Metabolites Produced by Esca-Associated Fungi and Enological Saccharomyces cerevisiae Strains

Esca-affected vines alter the carbohydrate metabolism, xylem transport of water and photosynthesis and show regular grapes (but berries do not reach maturity), and phenolic compounds are reduced in concentration, oxidate and polymerizate. Pullulan and a mixture of scytalone and isosclerone (9:1; w/w), secondary metabolites produced in vitro and in planta by Phaeoacremonium minimum (syn. P. aleophilum) and Phaeomoniella chlamydospora, were assayed against the strains Byosal HS1 and IOC 18-2007 in microvinifications with synthetic grape must. The presence of pullulan and pentaketides mix affects the growth and metabolism of the tested Saccharomyces cerevisiae strains. Assays at 100 and 1000 μg mL−1 inhibited the growth of both strains, while no effects were recorded when evaluated at 1 and 5 μg mL−1. In comparison with the controls, pullulan and the scytalone/isosclerone mixture at 10 μg mL−1 had a growth reduction, a lower alcohol yield, reduced the concentration of tartaric acid and malic acid; and slowed down the production of lactic acid, acetic acid and total polyphenol content of the tested S. cerevisiae strains. These metabolites could be applied as an alternative to the sulfite addition in the early stages of vinification to support the action of selected Saccharomyces. Appealing is the subtractive action of pullulan against tartaric acid. Further data are needed to confirm and validate the enological performance in freshly pressed grape juice.