Grape Stalk-Based Extracts Controlling Fruit Pathogenic Fungi as a Waste Biomass Valorization Alternative in Winemaking

Abstract

Grape stalks—the lignocellulosic skeleton of the grape raceme- are accumulated in massive piles immediately after harvest and become a concentrated pollutant. Fungi cause several rots in grapevine and other fruit cultivars and albeit biocontrol agents are available, superior technologies must be developed to rival synthetic counterparts. In this work, we describe the preparation of grape stalk lipophilic extracts from Malbec, Cabernet sauvignon, Chardonnay and Pedro Giménez as biocontrol tools against Aspergillus candidus, Penicillium chrysogenum, and Rhizopus sp., which are pathogenic for grapes and other fruits. Grape stalk extracts were obtained with hexane, diethyl ether, ethyl acetate, and ethanol. Yields were in the range of 1 to 23% w/w according to solvent polarity. Extracts were separated into lipophilic sub-extracts—yields varied from 70 up to 12% w/w due to solvent polarity. Sub-extracts were assayed for antifungal activity in vitro and the one obtained from Pedro Giménez with ethanol exhibited the broadest biocontrol spectrum at 2.5 × 104 mg/L. This sub-extract was separated into components by column chromatography to inquire further on its biocontrol activity. A bioactivity-guided test against Rhizopus sp. revealed that this effect relies on gamma-sitosterol and a biocontrol cut-off value of 5.1 × 103 mg/L was estimated.