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

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 ß-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 fresh mushroom off-flavor (FMOff) is due to several C8 compounds such as 1-octen-3-one, 1-octen-3-ol and 1-hydroxyoctan-3-one, among others. Recently, glycosidic precursors of some FMOff compounds have been identified in grape musts, but the evolution of such compounds during alcoholic fermentation (AF) remains poorly studied. Therefore, the aim of this work was to monitor both FMOff glycosidic precursors and volatile compounds during AF by comparing healthy and Crustomyces subabruptus-contaminated musts. For the first time, glycosidic analysis revealed the presence of 1-hydroxyoctan-3-one glycosides in the laboratory-contaminated musts, together with other FMOff glycosidic fractions already described in the literature. During AF, the FMOff glycosidic fraction decreased, even more in the case of 1-hydroxyoctan-3-one precursors. For the volatile FMOff compounds, their evolutions were both compound- and matrix-dependent except for 1-hydroxyoctan-3-one, which seemed to reach an identical threshold concentration in wine regardless of its initial level in contaminated musts.

First identification of a new molecule involved in the fresh mushroom off-flavor in wines: 1-hydroxyoctan-3-one.

The fresh mushrooms off-flavor (FMOff) has been appearing in wines since the 2000 s; the C8 compounds, 1-octen-3-one, 1-octen-3-ol and 3-octanol are involved in this specific taint, yet they alone do not fully explain its occurrence. The objective of this work was to identify by GC-MS new FMOff markers in contaminated matrices, to correlate compound levels with wine sensory characterization and to determine the sensory attributes of 1-hydroxyoctan-3-one, a new candidate involved in FMOff. In practice, grape musts were artificially contaminated with Crustomyces subabruptus, and fermented to obtain tainted wines. GC-MS analysis of contaminated musts and wines revealed the presence of 1-hydroxyoctan-3-one only in contaminated musts, and not in the healthy control. In a selection of 16 wines affected by FMOff, the level of 1-hydroxyoctan-3-one correlated significantly (r2 = 0.86) with sensory analysis scores. Finally, 1-hydroxyoctan-3-one was synthesized and found to generate a fresh mushroom aroma in a wine matrix.