Odor Characteristics of Novel Non-Canonical Terpenes

Several non-canonical, methylated terpenes have been described as products of genetically modified Escherichia coli recently, and the aroma properties of 28 odor-active methylated derivatives of prenol, isoprenol, bornane, camphene, carene, citronellol, fenchol, geraniol, limonene, linalool, terpineol, and farnesol were characterized for the first time in the current study. Twelve methylated monoterpenes exhibited a particularly intense and pleasant odor and were therefore chosen for the determination of their respective odor thresholds (OTs) in comparison to their non-methylated equivalents. In addition to the determination of OTs based on the literature value for the internal standard, (2E)-decenal, the threshold values of the compounds with individually determined OTs of the participants were calculated. This enabled a more precise identification of the OTs. Among the non-canonical terpenes, the lowest OTs in the air were found for 2-methyllinalool (flowery, 1.8 ng L^-1), 2-methyl-α-fenchol (moldy, 3.6 ng L^-1), 2-methylgeraniol (flowery, 5.4 ng L^-1), 2-methylcitronellol (citrus-like, 7.2 ng L^-1), and 4-methylgeraniol (citrus-like, 16 ng L^-1). The derivatives of geraniol, linalool, and citronellol showed very pleasant odor impressions, which could make them interesting for use as flavoring agents in the flavor and fragrance industry.