Samantha McKenna and Keith R. Cadwallader

Department of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign

Trace odorants are crucial to the flavor profile of well-balanced peppermint (Mentha piperita L.) oil. Certain lactones have been identified in peppermint oils and contribute important sweet, coconut, coumarin-like characteristics to the oils. Of these lactones, collectively known as “mint lactones”, (−)-mintlactone and (+)-isomintlactone are the most well characterized, although numerous others remain unidentified. Previous research has shown that mint lactones are present in peppermint oils and other materials containing menthofuran and can be synthesized by the oxidation of menthofuran. We hypothesize that menthofuran spontaneously degrades to form mint lactones, that the concentrations of mint lactones are directly related to the concentration of menthofuran in peppermint oil, and that mint lactones, though present in trace amounts, have low odor thresholds and contribute to the overall sensory perception of peppermint oils. A silica gel fractionation method was developed to isolate lactone compounds from peppermint oils and concentrate them for analysis. A model peppermint oil system was also developed and used to track the accumulation of lactone compounds over several months.  Five lactone compounds of sensory importance were identified and quantified by stable isotope dilution analysis (SIDA) in three peppermint oils. The two diastereomers of menthofurolactone were resolved using chiral gas chromatography and their odor characteristics and thresholds evaluated separately for the first time. The enantiomeric ratio of the two diastereomers was also found to be consistent across the different oils. The ability to produce menthofuran distinguishes M. piperita L. from the M. arvensis and M. spicata species, making the identification and characterization of mint lactones critical in understanding and developing peppermint oil flavor chemistry. The opportunity also exists to transform menthofuran, which contributes undesirable characteristics to peppermint oils, into compounds that enhance the flavor and quality of peppermint oil.