A common explanation of molecular recognition by the olfactory system posits that receptors recognize the structure or shape of the odorant molecule. We performed a rigorous test of shape recognition by replacing hydrogen with deuterium in odorants and asking whether Drosophila melanogaster can distinguish these identically shaped isotopes. We report that flies not only differentiate between isotopic odorants, but can be conditioned to selectively avoid the common or the deuterated isotope. Furthermore, flies trained to discriminate against the normal or deuterated isotopes of a compound, selectively avoid the corresponding isotope of a different odorant. Finally, flies trained to avoid a deuterated compound exhibit selective aversion to an unrelated molecule with a vibrational mode in the energy range of the carbon-deuterium stretch. These findings are inconsistent with a shape-only model for smell, and instead support the existence of a molecular vibrationsensing component to olfactory reception.

The objective of this work was to evaluate the effectiveness of antimicrobial edible coatings to wrap cheeses, throughout 60 d of storage, as an alternative to commercial nonedible coatings. Coatings were prepared using whey protein isolate, glycerol, guar gum, sunflower oil, and Tween 20 as a base matrix, together with several combinations of antimicrobial compounds-natamycin and lactic acid, natamycin and chitooligosaccharides (COS), and natamycin, lactic acid, and COS. Application of coating on cheese decreased water loss (~10%, wt/wt), hardness, and color change; however, salt and fat contents were not significantly affected. Moreover, the antimicrobial edible coatings did not permit growth of pathogenic or contaminant microorganisms, while allowing regular growth of lactic acid bacteria throughout storage. Commercial nonedible coatings inhibited only yeasts and molds. The antimicrobial edible coating containing natamycin and lactic acid was the best in sensory terms. Because these antimicrobial coatings are manufactured from food-grade materials, they can be consumed as an integral part of cheese, which represents a competitive advantage over nonedible coatings.

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Given the growing interest in high quality hibiscus teas and the scarcity of information about their sensory profile, lexicons were developed in French, Portuguese, and English. Twenty-two samples, including freshly prepared and ready-to-drink (RTD) infusions, syrups, concentrates, and an instant tea were evaluated by trained panelists, resulting in 21 defined and referenced descriptors, subsequently assembled in a sensory wheel. The vocabulary used by untrained panelists was investigated in Senegal, Portugal, France, and United Kingdom through professional meetings (n = 30), consumer focus groups (n = 75) and check-all-that-apply (CATA) studies (n = 490), resulting in graphical lexicons with 27 sensory and 15 overall impression terms. Training, food culture, and product familiarity influenced results. Trained panelists used precise terms to describe the aromatic profile of hibiscus teas (e.g., “reminiscent of dried hibiscus flowers,” with “berry,” “raisin,” “hay,” and “sweet” aromatic notes), whereas untrained ones were more prolific in general expressions (e.g., “strong in hibiscus” in Senegal; “floral” and “fruity” in Europe). Practical applications This work provides a foundation for sensory research on hibiscus teas and practical support for product optimization processes, whether through hibiscus cultivar selection and breeding, improvement of harvest and postharvest operations or tea processing methods. Moreover, new lexicons will facilitate communication between the actors involved in the development, production, and marketing of hibiscus extracts and products thereof across Africa, Europe, and North/South America. Finally, potential drivers of hibiscus tea acceptance in both traditional and new markets are also identified. (Résumé d'auteur

We would like to thank Dr. Hettinger (1) for his positive comment on our results showing that flies can discriminate isotopes by smell and are capable of cross-learning between odorants sharing a molecular vibration. Our article (2) demonstrated the presence of a physical (vibrational) component to odor character necessitating a vibration-sensing mechanism, the nature of which was not addressed experimentally and remains to be elucidated. We suggest that it likely involves inelastic electron tunneling, because this is consistent with our experimental data and with Brookes et al. (3), who have shown that an inelastic tunneling mechanism in olfaction is physically plausible. As pointed out by Luca Turin, this odorant detection mechanism does not require generation of free electrons by NADPH (4) and offers a potential explanation to why most enantiomer pairs smell identical. Further, Takane and Mitchell (5) have found IR spectra to be good predictors of odor character.In our article, we described data obtained for Drosophila olfaction; we did not discuss or extend our findings to vertebrate olfactory systems or claim that humans can smell isotopes. Hence, a description of how the deuterated odorants we use smell to humans is unnecessary. Several of the issues repeated here with respect to human olfaction were originally raised by Dr. Hettinger in the journal Chemical Senses in 2008 and answered by one of us (6). We seize this opportunity to point out the following: the change in C-H stretch frequency upon substitution by deuterium is indeed large, but its effect on odor character would be proportional to the intensity of the deuterium peak as measured by fly olfactory receptors, which is unknown at this stage and may be small, but nevertheless our experiments show that flies can consistently detect it.The notion that smell, like hearing and color vision, may be a spectral sense is indeed attractive, but this does not make it true. We have shown that in Drosophila one component of odorant recognition is conferred by molecular vibration, and this clearly implies a vibration-sensing mechanism. Another component to odor character could be the shape of the odorant molecules. If so, then olfaction in Drosophila combines both chemical (shape) and spectral (vibrations) components and may be evolutionarily intermediate between the purely spectral senses (vision and hearing) and a purely chemical one (taste). We further speculate that it is possible that vibration and shape sensing are used differentially for detection of different odorants. This, Dr. Hettinger argues, requires a continuous odor space, which he dismisses. However, this is at odds with the fact that odor character requires multiple descriptors (rosy, musky, woody, etc.), and their relative prominence in related odorants often varies in a strikingly continuous fashion. Finally, as Dr Hettinger points out, using vibrations to detect isotopes is likely not very important to Drosophila. However, because all molecules vibrate, sensing molecular vibrations may be a...