A new analytical method to measure S‐methyl‐l‐methionine in grape juice reveals the influence of yeast on dimethyl sulfide production during fermentation

BACKGROUND Dimethyl sulfide (DMS) is a small sulfur‐containing impact odorant, imparting distinctive positive and / or negative characters to food and beverages. In white wine, the presence of DMS at perception threshold is considered to be a fault, contributing strong odors reminiscent of asparagus, cooked cabbage, and creamed corn. The source of DMS in wine has long been associated with S‐methyl‐l‐methionine (SMM), a derivative of the amino acid methionine, which is thought to break down into DMS through chemical degradation, particularly during wine ageing. RESULTS We developed and validated a new liquid chromatography–tandem mass spectrometry (LC–MS/MS) method with a stable isotope dilution assay (SIDA) to measure SMM in grape juice and wine. The application of this new method for quantitating SMM, followed by the quantitation of DMS using headspace‐solid phase micro‐extraction coupled with gas chromatography–mass spectrometry (HS‐SPME/GC–MS), confirmed that DMS can be produced in wine via the chemical breakdown of SMM to DMS, with greater degradation observed at 28 °C than at 14 °C. Further investigation into the role of grape juice and yeast strain on DMS formation revealed that the DMS produced from three different Sauvignon blanc grape juices, either from the SMM naturally present or SMM spiked at 50 mmol L−1, was modulated depending on each of the four strains of Saccharomyces cerevisiae wine yeast used for fermentation. CONCLUSION This study confirms the existence of a chemical pathway to the formation of DMS and reveals a yeast‐mediated mechanism towards the formation of DMS from SMM during alcoholic fermentation. © 2019 Society of Chemical Industry