The 1-hydroxyoctan-3-one, a molecule potentially involved in the fresh mushroom off-flavor in wines

Abstract

An organoleptic defect, called fresh mushrooms off-flavor (FMOff), appeared in wines and spirits since the 2000’s. Numerous researches demonstrated that octen-3-one, 3-octanol and octen-3-ol (C8 compounds) were involved in the mushroom off-flavor in wines. Nevertheless, these molecules alone do not explain the entire defect in wines and some odorous zones still remain without chemical identification.  Recently, Crustomyces subabruptus has been shown to be a fungus capable of systematically producing FMOff under oenological conditions. The aim of this work was (a) to identify new markers of FMOff using Crustomyces subabruptus as a laboratory model, (b) to synthesize potential candidates and (c) to correlate the levels of these compounds determined by GC-MS with sensory characterization of healthy and affected wines. In practice, Pinot noir musts were artificially contaminated by Crustomyces subabruptus in the laboratory and then fermented. The musts and corresponding wines were analyzed in an untargeted way by GC-MS. By comparison with MS spectra libraries, the 1-hydroxy-3-octanone was formally and systematically identified in these matrices. This molecule, which has never been identified in grapes nor in wine, was only referenced in the fruit of the papaya mountain after enzymatic hydrolysis of the glycosidic fractions of the fruit pulp. In order to develop a targeted analysis by GC-MS, we synthesized the 1-hydroxy-3-octanone according to a previously published procedure. Briefly, 3-hydroxypropionitrile was first silylated to protect hydroxyl function and then reacted with pentylmagnesium bromide according to the Grignard reaction. The last step involved the deprotection of the resulting alcohol to obtain the expected product. Finally, 30 wines from different vintages (those of 2017, 2018, 2019, and 2021) on which were sensorially detected FMOff were spiked with deuterated internal standards (1-octen-3-one-d2, 1-octen-3-ol-d2, 3-octanol-d4), extracted with a pentane-dichloromethane mixture (2/1, v/v), rectified at 40°C, and then analyzed by GC-MS. The analysis of these wines showed the systematic presence of 1-hydroxy-3-octanone in the 2017 wines with levels that seemed to correlate significantly (test of spearman= 0,81) with the sensory analysis scores, r²=0.65. Wines with high sensory analysis scores for FMOff have a higher level of 1-hydroxyoctan-3-one than those with lower scores. On the other hand, the wines did not systematically contained octen-3-one, 3-octanol or octen-3-ol after 4 years of ageing, suggesting that 1-hydroxy-3-octanone could be a more stable chemical marker than the other compounds in the oenological matrix. In conclusion, 1-hydroxyoctan-3-one is a new molecular candidate for tracking the FMOff. Its formal identification completes the overview of the molecules involved in this defect and opens the way to a better understanding of the appearance and evolution of fresh mushrooms off flavors in wines.