Identification of a Glycosylated Fraction Involved in Mushroom Off-Flavors in Grapes: Influence of Gray Rot, Powdery Mildew and Crustomyces subabruptus

Abstract

An organoleptic defect, termed fresh mushroom off-flavor and mainly caused by the C8 compounds 1-octen-3-one, 3-octanol and 1-octen-3-ol, has been identified in wines and spirits since the 2000s. The aim of this work was to identify the presence of glycosidic precursors of these C8 compounds and to evaluate the influence of different molds on the glycosylated fractions of three grape varieties. Must samples contaminated by molds (gray rot, powdery mildew and Crustomyces subabruptus) and three levels of attack severity (from healthy to 10–15%) were studied. After a β-glycosidase treatment on Meunier and Pinot noir musts contaminated by Crustomyces subabruptus, 1-octen-3-one, 1-octen-3-ol and 3-octanol were identified by GC-MS, proving the existence of glycosidic fractions in the musts. A Pinot noir must contaminated by Crustomyces subabruptus displayed a 230% increase in the glycosylated fraction responsible for 1-octen-3-one in comparison with an uncontaminated sample. Powdery mildew did not appear to affect the levels of the studied glycosidic fractions in Chardonnay musts. Gray rot on Meunier and Pinot noir musts had opposite effects depending on glycoside type, decreasing the 1-octen-3-one fraction and increasing the 1-octen-3-ol fraction.

Evolution of Markers Involved in the Fresh Mushroom Off-Flavor in Wine During Alcoholic Fermentation

“…The 3-octanol levels ranged from 0.083 ± 0.02 to 0.33 ± 0.07 μg/L in healthy wines (Figure B). On the other hand, the quantities of 1-hydroxyoctan-3-one were much higher than those of the other compounds and ranged from 67 to 103 ± 26 μg/L, close to its olfactory perception threshold, 200 μg/L (Delcros et al) (Figure C). According to a study, 3-octanol concentrations remained unchanged during AF in a model medium, which differs from our observations.…”

“…For 3-octanol and 1-octen-3-ol, they were also identified as aglycones, which corroborates previous studies. Indeed, 3-octanol and 1-octen-3-ol glycosides had already been identified in Pinot noir and Meunier musts contaminated by Crustomyces subabruptus as well as in Chardonnay berry skins and wines …”

“…The TLC revelator was composed of a 1% KMnO 4 solution in water. The deuterated standards, 1-octen-3-one-d 2 and a mixture of 1-octen-3-ol-d 2 and 3octanol-d 4 , were synthesized following the protocols already established in the publication of Delcros et al 18 The synthesis of 1hydroxyoctan-3-one follows the same protocol as Husain et al 23 2.2. Samples from Laboratory Contamination Model.…”

“…FMOff character in wine could be due to glycosidic precursors present in grapes as recently reported in literature. 18 Considering this aspect, we decided to characterize the presence of the glycosidic precursors present in our grape juices as a starting point for our experiments. Due to the molecular complexity of glycosides, an indirect approach was chosen and based upon glycoside extraction, enzymatic cleavage by a β-glycosidase, and analysis of aglycones by GC-MS using both full scan and SIM modes focusing on C8 molecules, such as 1-octen-3-one, 1-octen-3-ol, 2-octanol, 3octanol, and 1-hydroxyoctan-3-one.…”

“…Sample Preparation. Glycoside extraction was based on the protocol established by Gunata et al 25 and modified by Delcros et al 18 In a concise manner, the extraction process for each sample was conducted in triplicate. A volume of 300 mL of grape must or wine was treated with 3 g of washed polyvinylpolypyrrolidone (PVPP, Sigma-Aldrich, France) for 20 min.…”