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The biocatalytic production of flavor naturals that determine chemosensory percepts of foods and beverages is an ever challenging target for academic and industrial research. Advances in chemical trace analysis and post-genomic progress at the chemistry-biology interface revealed odor qualities of nature's chemosensory entities to be defined by odorant-induced olfactory receptor activity patterns. Beyond traditional views, this review and meta-analysis now shows characteristic ratios of only about 3 to 40 genuine key odorants for each food, from a group of about 230 out of circa 10 000 food volatiles. This suggests the foodborn stimulus space has co-evolved with, and roughly match our circa 400 olfactory receptors as best natural agonists. This perspective gives insight into nature's chemical signatures of smell, provides the chemical odor codes of more than 220 food samples, and beyond addresses industrial implications for producing recombinants that fully reconstruct the natural odor signatures for use in flavors and fragrances, fully immersive interactive virtual environments, or humanoid bioelectronic noses.

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By application of the aroma extract dilution analysis on the volatile fraction isolated from a black tea infusion (Darjeeling Gold Selection), vanillin (vanilla-like), 4-hydroxy-2,5-dimethyl-3(2H)-furanone (caramel), 2-phenylethanol (flowery), and (E,E,Z)-2,4,6-nonatrienal (oat-flake-like) were identified with the highest flavor dilution (FD) factors among the 24 odor-active compounds detected in the FD factor range of 4-128. Quantitative measurements performed by means of stable isotope dilution assays and a calculation of odor activity values (OAVs; ratio of concentration to odor threshold in water) revealed, in particular, the previously unknown tea constituent (E,E,Z)-2,4,6-nonatrienal as a key odorant in the infusion and confirmed the important role of linalool and geraniol for the tea aroma. An aroma recombinate performed by the 18 odorants for which OAVs > 1 were determined in their "natural" concentrations matched the overall aroma of the tea beverage. In the black tea leaves, a total of 42 odorants were identified, most of which were identical with those in the beverage prepared thereof. However, quantitative measurements indicated that, in particular, geraniol, but also eight further odorants were significantly increased in the infusion as compared to their concentration in the leaves.

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Twelve odorants, previously identified with high flavor dilution (FD) factors, were quantified in a fresh strawberry juice by using stable isotope dilution assays. Calculation of odor activity values (ratio of concentration to odor threshold), on the basis of odor thresholds in water, revealed especially the six compounds (Z)-3-hexenal (green), 4-hydroxy-2,5-dimethyl-3(2H)-furanone (caramel-like, sweet), methyl butanoate (fruity), ethyl butanoate (fruity), methyl 2-methylpropanoate (fruity), and 2,3-butanedione (buttery) as the key flavor compounds in the typical strawberry-like odor of the juice. These results were corroborated by the following sensory experiments:  A mixture of the 12 most potent odorants added to a model juice matrix, consisting of pectin, sugars, and nonvolatile acids, in concentrations equal to those in the fresh juice, resulted in an overall odor profile very similar to that of the fresh juice. Furthermore, comparison of the overall odors of 11 model mixtures lacking in 1 of the 12 odorants under investigation, with the odor evoked by the complete set of odorants, showed a clear flavor difference, especially when 4-hydroxy-2,5-dimethyl-3(2H)-furanone, (Z)-3-hexenal, or methyl butanoate was lacking in the mixture. Keywords: Strawberry odor; stable isotope dilution assay; odor activity value; sensory study; [13C]2-2,3-butanedione; [2H3]methyl butanoate; [2H3]methyl 2-methylbutanoate; [2H3]ethyl butanoate; [2H3]-4-methoxy-2,5-dimethyl-3(2H)-furanone