R. Guzzon, E. Franciosi, S. Moser, I. Carafa, R. Larcher

Straw wine is an high-valuable oenological production, affected by relevant economical losses due to proliferation of spoilage microorganisms during drying grapes, after being harvested. In this work ozone was evaluated as tool to preserve grapes during drying, in terms of both qualitative and quantitative changes induced in the epiphytic microflora. In addition, the alteration exerted by ozone on grape's chemical composition was analyzed. Grapes from four vine varieties were treated with ozone produced by a cold plasma generator during the entire drying period (6 weeks). The microflora was quantified weekly by plate counts and characterized by 454-pyrosequencing, and was compared with identical, untreated, grape samples. At the end of drying, an extensive chemical characterization was performed onto the whole mass of grapes by FT-IR and GC-MS. Ozone counteracted the growth of microflora, by reducing the microbial population up to 3 log units. From the qualitative point of view, ozone reduced the incidence of spoilage microorganisms, such as Acetobacter and Botrytis cinerea, among the microbiota of grapes. The statistical analysis discriminates grape samples based on the residual epiphytic microflora at the end of drying and not on their chemical composition. These evidences confirmed that ozone did control spoilage microorganisms without altering the volatile profile of grapes. Chemical analysis revealed that untreated grapes are less suitable for winemaking owing to the deprivation of some valuable compounds during the microbial proliferation. This article is protected by copyright. All rights reserved.