Alternaria, Tenuazonic Acid and Spoilage Yeasts Associated with Bunch Rots of the Southern Oasis of Mendoza (Argentina) Winegrowing Region

Abstract

A study was carried out to identify the filamentous fungi and yeastspresent in rotten wine grapes from two subzones of the Southern oasis ofMendoza winegrowing region, to assess the occurrence of tenuazonic acid (TA), amycotoxin produced by the Alternariagenus, and to evaluate the wine spoilage potential of the associated yeasts invitro and during microvinifications. The main fungal genera present were Alternaria (69.3%), followed by Aspergillus (16.8%), Penicillium (9.3%) and Cladosporium (4.6%), while the dominantyeast species Metschnikowia pulcherrima(23.1%) were followed by Aureobasidium pullulans(20.2%), Hanseniaspora uvarum(13.0%), H. vineae (11.6%), Zygosaccharomyces bailii (10.4%), and H. guilliermondii (9.2%). Additionally,94.1% of the rotten samples were contaminated with TA, with the highest levelfound in Cabernet Sauvignon variety. No geographic association was found in theincidence of the different fungal genera or yeast species, nor in theoccurrence of TA. Almost all of the tested yeasts produced H₂S, the majority ofthe Hanseniaspora strains producedacetic acid, and only one M. pulcherrimastrain produced off-flavours in in vitro tests. Wines co-fermented with H.uvarum L144 and S. cerevisiae showed higher volatile acidity andlower fruity aroma and taste intensity. Therefore, processing bunch rot couldpose a toxicological and microbiological risks to winemaking due to the highincidence of Alternaria and TA, as well as the potential of theassociated yeasts to spoil wine.