IMPACT OF GRAPE-ASSOCIATED MOLDS IN FRESH MUSHROOM AROMA PRODUCTION

Abstract

Mycobiota encountered from vine to wine is a complex and diversified ecosystem that may impact grape quality at harvest and the sensorial properties of wines, thus leading to off-flavors [1-3]. Among known off-flavors in wine, fresh mushroom aroma (FMA) has been linked to some mold species, naturally pre-sent on grapes, producing specific volatile organic compounds (VOC) [4-5]. The most well-known are 1-octen-3-ol and 1-octen-3-one, although many other VOC are likely involved. To better understand the FMA defect, biotic and abiotic factors impacting growth kinetics and VOC production of selected fungal species in must media and on grapes were studied. In total, 18 fungal isolates, belonging to 7 genera and 9 species, were selected based on their off-odor production profiles on malt medium among 685 isolates from our working collection. Growth rates were measured using solid synthetic must (MS) and real must (MR) and compared to those obtained in liquid must by laser nephelometry. Sensorial analysis and VOC profiles (GC-MS) were also determined for the same isolates, individually or in co-cultures with two FMA producing Botrytis isolates, after growth on must and grapes. Among the generated physiological data, optimal growth temperatures were 27-28°C, 26-30°C, 21-22°C for Botrytis spp., Penicillium crocicola and P. citreonigrum, respectively, depending on the isolate. Fastest growth rates were observed for B. cinerea and P. crocicola, while Cladosporium subtilissimum and P. brevicompactum isolates were slowest. For VOC profiles, P. crocicola, P. bialowiezense and Clonostachys rosea produced known FMA compounds (1-octen-3-one and 1-octen-3-ol) at higher levels when co-inoculated with Botrytis spp. on grapes. For must trials, a species effect on VOC profiles was clearly observed (92 VOC identified). To confirm these findings, further co-inoculation studies were performed on two grape varieties (Meunier and Pinot noir) and, so far, sensorial analyses showed similar trends. Overall, this study provides novel knowledge about changes in fungal growth kinetics and VOC profiles in musts and on grapes. These results provide new insights for the wine making to better understand how FMA off-flavors are generated by molds.