Basic and Neutral Compounds in the Cooked Odor from Antarctic Krill

The cooked odor concentrate from precooked krill was obtained by a simultaneous distillation and extraction system. The resulting odor concentrate was separated into basic, carbonyl and carbonyl-free fractions. Each fraction was analyzed by gas chromatography and gas chromatography-mass spectrometry. Fifty seven compounds, including 3 pyridines, 10 pyrazines, 6 thiazoles, 3 dihydro-4H-1,3,5-dithiazines, 11 aldehydes, 10 ketones, 4 alcohols, 6 hydrocarbons and 4 other compounds were identified. Twenty two of these compounds were newly found as the odor components of krill. The low molecular aldehydes, which are known to be a part of the precursors of the secondary formation of the cooked odor, were also investigated by thin layer chromatography. Ethanal, propanal and butanal were newly detected.     

Predicting Odor Perceptual Similarity from Odor Structure

To understand the brain mechanisms of olfaction we must understand the rules that govern the link between odorant structure and odorant perception. Natural odors are in fact mixtures made of many molecules, and there is currently no method to look at the molecular structure of such odorant-mixtures and predict their smell. In three separate experiments, we asked 139 subjects to rate the pairwise perceptual similarity of 64 odorant-mixtures ranging in size from 4 to 43 mono-molecular components. We then tested alternative models to link odorant-mixture structure to odorant-mixture perceptual similarity. Whereas a model that considered each mono-molecular component of a mixture separately provided a poor prediction of mixture similarity, a model that represented the mixture as a single structural vector provided consistent correlations between predicted and actual perceptual similarity (r≥0.49, p<0.001). An optimized version of this model yielded a correlation of r = 0.85 (p<0.001) between predicted and actual mixture similarity. In other words, we developed an algorithm that can look at the molecular structure of two novel odorant-mixtures, and predict their ensuing perceptual similarity. That this goal was attained using a model that considers the mixtures as a single vector is consistent with a synthetic rather than analytical brain processing mechanism in olfaction.     

恶臭的生物治理技术

介绍恶臭的危害、种类和特性 ,侧重论述生物治理的常规方法、微生物机理等方面的研究成果及其展望。     

Odor sensitivity to geosmin enantiomers

Enantiomers of the earthy smelling odorant ‘geosmin’(t-1, 10-dimethyl-t-9-decalol) were tested on 52 human subjectsfor odor threshold ratio (+)/(–) variability. Thresholdconcentrations of (+) and (–) and their (+)/(–)ratios appeared to be monomodally distributed. For most subjects,the ratio varied within a predictable narrow range comparableto that found previously for carvone enantiomers and contraryto the large variability found for -ionone enantiomers (Polaket al., 1989). The natural occurring isomer, (–) geosminhad, on average an x11 lower threshold than (+).     

Odor psychophysics and sensory engineering

This paper illustrates the utilization of psychophysical scalingand optimization technology to accomplish two goals. First,by means of ‘goal programming’ the odor scientistcan interrelate chemicals and odor qualities, specify a desiredprofile of odor qualities and determine that combination ofodorants which come as close as possible to generating thatdesired profile. Second, by means of non-linear optimization,the scientist can determine the relation between chemical concentrationsand liking, and furthermore ascertain that combination of chemicalconcentrations which generate maximal liking ratings, subjectto constraints. Constraints include chemical concentrationslying within prespecified limits, and sensory perceptions lyingwithin specific bounds. Mixtures of butyric acid and pulegoneillustrate the approach.     

Segregation of Odor Identity and Intensity during Odor Discrimination in Drosophila Mushroom Body

Molecular and cellular studies have begun to unravel a neurobiological basis of olfactory processing, which appears conserved among vertebrate and invertebrate species. Studies have shown clearly that experience-dependent coding of odor identity occurs in “associative” olfactory centers (the piriform cortex in mammals and the mushroom body [MB] in insects). What remains unclear, however, is whether associative centers also mediate innate (spontaneous) odor discrimination and how ongoing experience modifies odor discrimination. Here we show in naïve flies that G_αq-mediated signaling in MB modulates spontaneous discrimination of odor identity but not odor intensity (concentration). In contrast, experience-dependent modification (conditioning) of both odor identity and intensity occurs in MB exclusively via G_αs-mediated signaling. Our data suggest that spontaneous responses to odor identity and odor intensity discrimination are segregated at the MB level, and neural activity from MB further modulates olfactory processing by experience-independent G_αq-dependent encoding of odor identity and by experience-induced G_αs-dependent encoding of odor intensity and identity.     

Odor similarities in structurally related odorants

Similarity assessments against one or several references wereused to estimate "earthiness" in 7 pure cyclic alcohols. The "earthy" odor quality of 3 isomers (I, II, IV) of the moldmetabolite "geosmin" (1, 10dimethyl-9-decalol C₁₂H₂₂O) was foundto be present in 2 other alcohols possessing a partial geosminstructure: exo-2-ethyl-fenchol (C₁₁H₂₂O) (V) and cis-cis 2,6-di-methyl-cyclohexanol(C₈H₁₆O) (VI). All have in common an axial hydroxy group attachedto a 5 or 6 carbon ring with alpha methyls on both sides. The trans-cis and trans-trans isomers of 2,6 dimethyl cyclohexanol(VII, VIII) both with equatorial hydroxy groups, were rankedas different from the above group. Instead their odor resemblesmore that of their aromatic precursor — 2,4 dimethyl phenol(IX) — than that of their axial isomer (VI). The two trans-ring geosmin isomers (I,II) and 2-ethylfenchol(V) were still judged earthy at up to 1000x the lowest concentrationtested. However, the cis-ring geosmin isomer (IV) and the axial cyclohexanol(VI) were perceived by most subjects to change in quality: earthyat lower concentrations but increasingly different at higherones. Discrimination between earthy odorants decreased with decreasingconcentration. Geosmins I, IV and 2 ethyl-fenchol (V) were particularlyconfused. However, discrimination did not appear to be affectedby prior adaptation to geosmin IV. Subjects appeared to be able to focus on the earthy odor qualitycomponent in single odorants IV, V, VI in which several otherquality components could be discerned as well.     

Odor Perception and Beliefs about Risk

Although the perceptual response to environmental odors canbe quite variable, such variation has often been attributedto differences in individual sensitivity. An information-processinganalysis of odor perception, however, treats both the receptionand the subsequent evaluation of odor information as determinantsof the perceptual response. Two experiments investigated whethera factor that influenced the evaluation stage affected the judgementof odor quality and the degree of adaptation to the odor. Peoplewere surveyed in order to measure their tacit perceptions ofthe healthfulness or hazardousness of nine common olfactorystimuli, and the instructional context influenced quality perception.In a second experiment subjects were exposed to an ambient odorunder one of three different conditions, and odorant characterizationinfluenced the degree of adaptation to the odor. Subjects whowere led to believe the odor was a natural, healthy extractshowed adaptation; those told that the odor was potentiallyhazardous showed apparent sensitization; while those told thatthe odor was a common olfactory test odorant showed a mixedpattern: some exhibited adaptation, whereas others showed sensitization.However, detection thresholds obtained before and after exposureshowed adaptation effects that are characteristic of continuousexposure. These findings raise the possibility that cognitivefactors may be modulating the overall sensory perception ofodor exposure (i) for some individuals who exhibit extreme sensitivityto odors and (ii) in situations where adaptation to environmentalodors is expected but does not occur. Chem. Senses 21: 447–458,1996.     

Odor coding in the Drosophila antenna

Odor coding in the Drosophila antenna is examined by a functional analysis of individual olfactory receptor neurons (ORNs) in vivo. Sixteen distinct classes of ORNs, each with a unique response spectrum to a panel of 47 diverse odors, are identified by extracellular recordings. ORNs exhibit multiple modes of response dynamics: an individual neuron can show either excitatory or inhibitory responses, and can exhibit different modes of termination kinetics, when stimulated with different odors. The 16 ORN classes are combined in stereotyped configurations within seven functional types of basiconic sensilla. One sensillum type contains four ORNs and the others contain two neurons, combined according to a strict pairing rule. We provide a functional map of ORNs, showing that each ORN class is restricted to a particular spatial domain on the antennal surface.     

Cooked Odor of Euphausia pacifica Hansen

Quinoxaline and benzimidazole derivatives obtained from L-rhamnose and L-fucose under deoxygenated, weakly acidic, heated conditions were studied using GLC, HPLC, and NMR.

Four quinoxalines and one benzimidazole were obtained from L-rhamnose (RHA-I, II, III, III′, and IV) and L-fucose (FUA-I, II, III, IV, and V) in an acidic solution (MeOH-AcOH-H₂I = 8 : 1 : 2) at 80°C. The total yield of the products as sugar was about 80% from either rhamnose or fucose.

The structure of RHA-I was (2′S)-2-methyl-3-(2′-hydroxypropyl)quinoxaline; RHA-II, (2′R,3′S)-2-(2′,3′-dihydroxybutyl)quinoxaline; RHA-III, (1′S,2′S,3′S)-2-(1′2′3′-trihydroxybutyl)quinoxaline[2-(L-arabino-1′,2′,3′-trihydroxybutyl)quinoxaline]; RHA-III′, 2-(L-ribo-1′,2′,3′-trihydroxybutyl)quinoxaline; and RHA-IV, 2-(L-manno-1′,2′,3′,4′-tetrahydroxypentyl)-benzimidazole, and the structure of FUA-I was the same as RHA-I; FUA-II, (2′S, 3′S)-2-(2′, 3′-dihydroxybutyl)quinoxaline; FUA-III, (1′R, 2′R, 3′S)-2-(1′,2′,3′-trihydroxybutyl)quinoxaline [2-(L-xylo-1′,2′,3′-trihydroxybutyl)quinoxaline; FUA-IV, 2-(L-lyxo-1′,2′,3′-trihydroxybutyl)-quinoxaline; and FUA-V, 2-(L-galacto-1′,2′,3′,4′-tetrahydroxypentyl)benzimidazole. These results suggest no significant difference for the pathways of quinoxaline and benzimidazole formation between L-rhamnose and L-fucose. Possible pathways are proposed for each sugar.     

Spatial Receptive Fields for Odor Localization

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Visualization of Fruit Odor by Photoluminescence

Photoluminescence with visible emission spectrum was observed and visualized at the surface of certain fruits. This photoluminescence is associated with vapors of natural organic volatiles (odorants) emitted from the fruit surface. The photoluminescence spectra of various fruits (apple, pear, kiwi, and strawberry) were measured in vivo using a number of fluorometric methods. Fruit aging was found to be accompanied by modification of the photoluminescence spectrum shape and a noticeable increase in the photoluminescence intensity. Laser photoluminescence microscopy in vapors of fruit extracts and artificial compounds was used to assess the contribution of various substances to natural odor emission of fruits. The results of this study show that fluorometry of odors is a promising method for studying fruits and other objects.