Perceptual interactions in odour mixtures: odour quality in binary mixtures of woody and fruity wine odorants

The qualitative perceptual interactions in three binary mixtures of wine odorants were studied: isoamyl acetate (fruity note)/whisky lactone (woody note), ethyl butyrate (fruity note)/whisky lactone (woody note) and ethyl butyrate (fruity note)/guaiacol (woody note). For each binary mixture, the perceived quality and intensity of 24 stimuli (four supra-threshold concentration levels of each of the two compounds and their 16 possible combinations) were evaluated in five replications by a trained panel of 13 subjects. The application of the Olsson predictive model for odour intensity and quality perception gave quite a good estimation of the evolution of single component identification in the mixture when the intensity proportion of unmixed components varied. However, this model was unable to account for the odour quality dominance in mixtures of iso-intense components. An alternative linear logistic model was proposed to study the qualitative dominance of the woody note in the three mixtures when the perceived intensities of each unmixed compound were equal.     

An Equiratio Mixture Model for Non-additive Components: A Case Study for Aspartame/Acesulfame-K Mixtures

The Equiratio Mixture Model predicts the psychophysical functionfor an equiratio mixture type on the basis of the psychophysicalfunctions for the unmixed components. The model reliably estimatesthe sweetness of mixtures of sugars and sugar-alchohols, butis unable to predict intensity for aspartame/sucrose mixtures.In this paper, the sweetness of aspartame/acesulfame-K mixturesin aqueous and acidic solutions is investigated. These two intensivesweeteners probably do not comply with the model's originalassumption of sensory dependency among components. However,they reveal how the Equiratio Mixture Model could be modifiedto describe and predict mixture functions for non-additive substances. To predict equiratio functions for all similar tasting substances,a new Equiratio Mixture Model should yield accurate predictionsfor components eliciting similar intensities at widely differingconcentration levels, and for substances exhibiting hypo- orhyperadditivity. In addition, it should be able to correct violationsof Stevens's power law. These three problems are resolved ina model that uses equi-intense units as the measure of physicalconcentration. An interaction index in the formula for the constantaccounts for the degree of interaction between mixture components.Deviations from the power law are corrected by a nonlinear responseoutput transformation, assuming a two-stage model of psychophysicaljudgment. Chem. Senses 21: 1–11, 1996.     

Development of a Partial Least Squares–Based Integrated Addition Model for Predicting Mixture Toxicity

Concentration addition (CA) and independent action (IA) models are often applied to estimate the mixture toxicity of similarly and dissimilarly acting chemicals, respectively. An integrated addition model (IAM), called the “integrated CA with IA based on a multiple linear regression (ICIM) model” was recently proposed for predicting additive toxicity of non-interactive mixtures regardless of whether mixture components produce similar, dissimilar, or both similar and dissimilar modes of action. In the ICIM, the effective concentrations of mixtures experimentally tested were regarded as the response variable, and the results estimated by CA and IA were considered as the predictor variable. However, it can be highlighted that the multicollinearity problem (i.e., a linear relationship between predictor variables), which may be caused in the existing ICIM model employing ordinary least squares regression. Therefore, the objectives of this study were to develop and evaluate a Partial Least Squares-based IAM (PLS-IAM) not only to overcome the multicollinearity problem, but also to combine the CA and IA into an IAM using the latent variable that accounts for most of the variation in the response. Through four test datasets, this study showed that the PLS-IAM overall outperformed the other reference models, including the CA, IA, and ICIM models.     

Taste Responses to Binary Mixtures of Amino Acids in the sea catfish, Arius felis

In vivo electrophysiological recordings in the sea catfish,Arius felis, showed that the magnitude of the integrated facialtaste responses to binary mixtures of amino acids was predictablewith knowledge obtained from previous cross-adaptation studiesof the relative independence of the respective binding sitesof the component stimuli. Each component from which equal aliquotswere drawn to form the mixtures was adjusted in concentrationto provide for approximately equal reponse magnitudes. The magnitudeof the taste responses to binary mixtures whose component aminoacids showed minimal cross-adaptation was significantly greaterthan that to binary mixtures whose components exhibited considerablecross-reactivity. There was no evidence for mixture suppression.The relative magnitude of the taste responses in the sea catfishto stimulus mixtures is similar to that previously reportedfor olfactory receptor responses in the freshwater channel catfishand chorda tympani taste responses in the hamster. Chem. Senses21: 45–53, 1996.     

Odor intensity of binary mixtures of odorous compounds

This paper presents the MBO model for the perceived intensity of odour mixtures. This model is based on an equation previously reported by our team, intended to model the whole stimulus-response intensity curve of pure odorous compounds. The MBO model was applied to a set of published data, and compared to other published models. The results show a high modelling efficiency of the MBO model compared to other proposed equations, especially for binary mixtures exhibiting significant asymmetry of intensity for different ratios of the two components. Furthermore, the MBO model includes parameters specific to the respective effects of each component in the mixture, which may help to clarify the masking and synergy effects that are often sought in odour mixtures.     

Inhibitory receptor binding events among the components of complex mixtures contribute to mixture suppression in responses of olfactory receptor neurons of spiny lobsters

Responses of olfactory receptor neurons of spiny lobsters Panulirus argus to two-component mixtures can be shaped by inhibitory events such as odor-activated hyperpolarizations and inhibition of odor-receptor binding (Daniel et al. 1996). In the current study, we extend this analysis to complex mixtures by examining responses of spiny lobster olfactory receptor neurons to mixtures containing up to seven odorants, consisting of adenosine-5′-monophosphate, ammonium, betaine, l-cysteine, l-glutamate, dl-succinate, and taurine. The response to a mixture was often less than the response to its most excitatory component. The effect of adding an excitatory odorant to a mixture depended on olfactory receptor neuron type, composition of the mixture, and which compound was added. In some cases the added excitatory compound had no effect or even decreased the mixture's response intensity, thus demonstrating nonlinear contributions of the components. Response intensities predicted by a noncompetitive model, which is most representative of these olfactory receptor neurons, were improved when the model included a term for empirical measurements of inhibitory binding interactions, suggesting that inhibitory binding interactions are one mechanism contributing to mixture suppression. This model's predictions were accurate for binary mixtures but not for larger mixtures, suggesting that additional inhibitory mechanisms are needed to account for mixture interactions in complex mixtures. Accepted: 24 July 1998     

Behavioral resolution of quality of odorant mixtures by spiny lobsters: differential aversive conditioning of olfactory responses

A differential aversive associative conditioning paradigm wasused to demonstrate the ability of spiny lobsters to discriminatebehaviorally between four 41-component chemical mixtures. Thesemixtures were based on natural extracts of crab, mullet, oysterand shrimp. Previously, we demonstrated, using the same paradigm,that lobsters conditioned to avoid the shrimp mixture coulddiscriminate, to varying degrees, between the shrimp mixtureand the other three mixtures. The present study was performedto compare the perceived quality of all four mixtures. Thiswas accomplished by conditioning four groups of animals, eachgroup to a different mixture type, and then using multidimensionalscaling (MDS) analysis to compare simultaneously the similaritiesand dissimilarities among the four mixtures as inferred by passiveand active avoidance behaviors. These two types of behaviorsrevealed different aspects of the discrimination: greater differentiationof the conditioned mixture from the non-conditioned mixtureswas indicated by active avoidance behavior, while gradationsin the degree of discrimination between the conditioned mixtureand each of the non-conditioned mixtures were indicated by passiveavoidance behaviors. Overall, lobsters perceived crab and shnmpmixtures as being similar to one another and dissimilar to mulletand oyster mixtures, while they perceived mullet and oystermixtures to be dissimilar to one another and to the crab andshrimp mixtures. Comparison of results from MDS analyses ofbehavioral mixture discrimination, neural mixture discriminationand mixture compositions may be used both to provide an indicationof the type of neural coding used to make these behavioral discriminationsand to identify the components of the mixtures that are responsiblefor recognition of and differential response to the mixtures.     

Olfactory discrimination of complex mixtures of amino acids by the black bullhead Ameiurus melas

On the basis of previous findings of behavioural discrimination of amino acids and on the knowledge of electrophysiology of the catfish (genera Ictalurus and Ameiurus) olfactory organs, behavioural experiments that investigated olfactory discrimination of amino acid mixtures were carried out on the black bullhead Ameiurus melas. Repeated presentations of food‐rewarded mixtures released increased swimming activity measured by counting the number of turns >90° within 90 s of stimulus addition. Non‐rewarded amino acids and their mixtures released little swimming activity, indicating that A. melas discriminated between the conditioned and the non‐conditioned stimuli. Two questions of mixture discrimination were addressed: (1) Are A. melas able to detect components within simple and complex amino acid mixtures? (2) What are the smallest differences between two complex mixtures that A. melas can detect? Three and 13 component mixtures tested were composed primarily of equipotent amino acids [determined by equal electroolfactogram (EOG) amplitude] that contained L‐Cys at ×100 the equipotent concentration. Ameiurus melas initially perceived the ternary amino acid mixture as its more stimulatory component alone [i.e. cysteine (Cys)], whereas the conditioned 13 component mixture containing the more stimulatory L‐Cys was perceived immediately as different from L‐Cys alone. The results indicate that components of ternary mixtures are detectable by A. melas but not those of more complex mixtures. To test for the smallest detectable differences in composition between similar multimixtures, all mixture components were equipotent. Initially, A. melas were unable to discriminate the mixtures of six amino acids from the conditioned mixtures of seven amino acids, whereas they discriminated immediately the mixtures of four and five amino acids from the conditioned mixture. Experience with dissimilar mixtures enabled the A. melas to start discriminating the seven‐component conditioned mixture from its six‐component counterparts. After fewer than five training trials, A. melas discriminated the mixtures of nine and 10 amino acids from a conditioned mixture of 12 equipotent amino acids; however, irrespective of the number of training trials, A. melas were unable to discriminate the 12 component mixture from its 11 component counterparts.     

Effects of binary taste stimuli on the neural activity of the hamster chorda tympani

Binary mixtures of taste stimuli were applied to the tongue of the hamster and the reaction of the whole corda tympani was recorded. Some of the chemicals that were paired in mixtures (HCl, NH4Cl, NaCl, CaCl2, sucrose, and D-phenylalanine) have similar tastes to human and/or hamster, and/or common stimulatory effects on individual fibers of the hamster chorda tympani; other pairs of these chemicals have dissimilar tastes and/or distinct neural stimulatory effects. The molarity of each chemical with approximately the same effect on the activity of the nerve as 0.01 M NaCl was selected, and an established relation between stimulus concentration and response allowed estimation of the effect of a "mixture" of two concentrations of one chemical. Each mixture elicited a response that was smaller than the sum of the responses to its components. However, responses to some mixtures approached this sum, and responses to other mixtures closely approached the response to a "mixture" of two concentrations of one chemical. Responses of the former variety were generated by mixtures of an electrolyte and a nonelectrolyte and the latter by mixtures of two electrolytes or two nonelectrolytes. But, beyond the distinction between electrolytes and nonelectrolytes, the whole-nerve response to a mixture could not be predicted from the known neural or psychophysical effects of its components.     

MMG: a probabilistic tool to identify submodules of metabolic pathways

Motivation: A fundamental task in systems biology is the identificationof groups of genes that are involved in the cellular responseto particular signals. At its simplest level, this often reducesto identifying biological quantities (mRNA abundance, enzymeconcentrations, etc.) which are differentially expressed intwo different conditions. Popular approaches involve using t-teststatistics, based on modelling the data as arising from a mixturedistribution. A common assumption of these approaches is thatthe data are independent and identically distributed; however,biological quantities are usually related through a complex(weighted) network of interactions, and often the more pertinentquestion is which subnetworks are differentially expressed,rather than which genes. Furthermore, in many interesting cases(such as high-throughput proteomics and metabolomics), onlyvery partial observations are available, resulting in the needfor efficient imputation techniques. Results: We introduce Mixture Model on Graphs (MMG), a novelprobabilistic model to identify differentially expressed submodulesof biological networks and pathways. The method can easily incorporateinformation about weights in the network, is robust againstmissing data and can be easily generalized to directed networks.We propose an efficient sampling strategy to infer posteriorprobabilities of differential expression, as well as posteriorprobabilities over the model parameters. We assess our methodon artificial data demonstrating significant improvements overstandard mixture model clustering. Analysis of our model resultson quantitative high-throughput proteomic data leads to theidentification of biologically significant subnetworks, as wellas the prediction of the expression level of a number of enzymes,some of which are then verified experimentally. Availability: MATLAB code is available from http://www.dcs.shef.ac.uk/~guido/software.html Contact: guido{at}dcs.shef.ac.uk Supplementary information: Supplementary data are availableat Bioinformatics online. Associate Editor: Jonathan Wren     

Prediction of Sweetness Intensity for Equiratio Aspartame/Sucrose Mixtures

The Equiratio Mixture Model predicts the responses to a seriesof equiratio mixtures on the basis of the psychophysical functionsfor the unmixed components. The model predicts the sweetnessof mixtures of sugars and sugar-alcohols successfully, but isunable to predict mixture intensity for substances with differentdynamic ranges. In this paper, the equi-intensity concept isintroduced in the Equiratio Mixture Model by transforming thephysical concentrations expressed in molarity into units thatproduce approximately equi-intense sensations. An empiricaltest using aspartame/sucrose mixtures shows that the modifiedEquiratio Mixture Model yields good predictions of mixture intensities.     

Stabilization of yield in plant genotype mixtures through compensation rather than complementation

Background and Aims

Plant genotypic mixtures have the potential to increase yield stability in variable, often unpredictable environments, yet knowledge of the specific mechanisms underlying enhanced yield stability remains limited. Field studies are constrained by environmental conditions which cannot be fully controlled and thus reproduced. A suitable model system would allow reproducible experiments on processes operating within crop genetic mixtures.

Methods

Phenotypically dissimilar genotypes of Arabidopsis thaliana were grown in monocultures and mixtures under high levels of competition for abiotic resources. Seed production, flowering time and rosette size were recorded.

Key Results

Mixtures achieved high yield stability across environments through compensatory interactions. Compensation was greatest when plants were under high levels of heat and nutrient stress. Competitive ability and mixture performance were predictable from above-ground phenotypic traits even though below-ground competition appeared to be more intense.

Conclusions

This study indicates that the mixing ability of plant genotypes can be predicted from their phenotypes expressed in a range of relevant environments, and implies that a phenotypic screen of genotypes could improve the selection of suitable components of genotypic mixtures in agriculture intended to be resilient to environmental stress.     

Qualitative and aqualitative intensity components of odour mixtures

The perception of the intensity of components of odorous mixturesis related to the overall mixture intensity in a complex mannerwhich has not so far been adequately modelled. Hypoadditivity,where the total perceived intensity of a mixture is less thanthe sum of the component intensities which arise when the substancesare presented in pure form at equivalent chemical concentrations,has been known for many years. An experiment on series of 56mixtures of amyl butyrate and bergamot at supra-threshold concentrationsfound that the total qualitatively unspecified intensity ofsuch mixtures can be greater than the sum of the identifiedcomponent intensities as judged in the context of the mixture.To reconcile an apparent contradiction, and to bring into onepsychophysical framework results from diverse procedures, amodel of mixed qualitative and aqualitative odour intensityis advanced, incorporating some evidence on the difference betweendetection and recognition processes. Each component in a mixturemay, in this theory, both partially mask the qualitative intensityof the other, and simultaneously convert some part of the other'sintensity into an aqualitative form.     

Honeybees Learn Odour Mixtures via a Selection of Key Odorants

Background

The honeybee has to detect, process and learn numerous complex odours from her natural environment on a daily basis. Most of these odours are floral scents, which are mixtures of dozens of different odorants. To date, it is still unclear how the bee brain unravels the complex information contained in scent mixtures.

Methodology/Principal Findings

This study investigates learning of complex odour mixtures in honeybees using a simple olfactory conditioning procedure, the Proboscis-Extension-Reflex (PER) paradigm. Restrained honeybees were trained to three scent mixtures composed of 14 floral odorants each, and then tested with the individual odorants of each mixture. Bees did not respond to all odorants of a mixture equally: They responded well to a selection of key odorants, which were unique for each of the three scent mixtures. Bees showed less or very little response to the other odorants of the mixtures. The bees'' response to mixtures composed of only the key odorants was as good as to the original mixtures of 14 odorants. A mixture composed of the other, non-key-odorants elicited a significantly lower response. Neither an odorant''s volatility or molecular structure, nor learning efficiencies for individual odorants affected whether an odorant became a key odorant for a particular mixture. Odorant concentration had a positive effect, with odorants at high concentration likely to become key odorants.

Conclusions/Significance

Our study suggests that the brain processes complex scent mixtures by predominantly learning information from selected key odorants. Our observations on key odorant learning lend significant support to previous work on olfactory learning and mixture processing in honeybees.     

EEG and sleep disturbances during dives at 450msw in helium-nitrogen-oxygen mixture

Rostain, J. C., M. C. Gardette-Chauffour, and R. Naquet. EEG and sleep disturbances during dives at450 msw in helium-nitrogen-oxygen mixture. J. Appl.Physiol. 83(2): 575-582, 1997.To study the effects of nitrogen addition to the breathing mixture on sleep disturbances at pressure, two dives were performed in whichhelium-nitrogen-oxygen mixture was used up to 450 m sea water (msw). Intotal, sleep of 12 professional divers was analyzed (i.e., 184 nightrecords). Sleep was disrupted by compression and by stay at 450 msw: we observed an increase in awake periods and in sleep stages I and II anda decrease in stages III and IV and in rapid-eye-movement sleepperiods. These changes, which were more intense at thebeginning of the stay, began to decrease from the seventh day of thestay, but the return to control values was recorded only during the decompression at depths below 200 msw. These changes were equivalent tothose recorded in other experiments with helium-oxygen mixture in thesame range of depths and were independent of the intensity of changesrecorded in electroencephalographic activities in awake subjects.

     

An analytical pipeline for genomic representations used for cytosine methylation studies

Motivation: Representations of the genome can be generated bythe selection of a subpopulation of restriction fragments usingligation-mediated PCR. Such representations form the basis fora number of high-throughput assays, including the HELP assayto study cytosine methylation. We find that HELP data analysisis complicated not only by PCR amplification heterogeneity butalso by a complex and variable distribution of cytosine methylation.To address this, we created an analytical pipeline and novelnormalization approach that improves concordance between microarray-deriveddata and single locus validation results, demonstrating thevalue of the analytical approach. A major influence on the PCRamplification is the size of the restriction fragment, requiringa quantile normalization approach that reduces the influenceof fragment length on signal intensity. Here we describe allof the components of the pipeline, which can also be appliedto data derived from other assays based on genomic representations. Contact: jgreally{at}aecom.yu.edu Supplementary information: Supplementary data are availableat Bioinformatics online. Associate Editor: Joaquin Dopazo     

Intensity and hedonic judgments of taste mixtures: an information integration analysis

Anderson's (1981) information integration approach was usedto examine taste mixture integration for intensity and hedonicjudgments of sucrose/sodium chloride and sucrose/citnc acidsolutions. In Experiment I, total intensity and hedonic ratingswere made for factorial combinations of sucrose and sodium chlorideor citric acid. The total intensity judgments produced an integrationpattern characterized by extreme subadditivity at high soluteconcentrations. (Subadditivity refers to the tendency for totalmixture intensity to be rated as less than the sum of the unmixedcomponent intensities.) The intensity judgment integration patternswere essentially identical for the two mixture types. However,the pattern of integration for the sucrose/sodium chloride andsucrose/citric acid mixtures differed for the hedonic ratings.Sucrose tended to eliminate the unpleasantness associated withincreasing concentrations of citric acid, while it only modulatedthis trend for sodium chloride. In Experiment II, subjects ratedthe individual sweet, salty and sour components of the mixturesto determine whether mixture suppression of the component tastescould account for the subadditivity of the total intensity judgmentsand/or the pattern of results for the hedonic ratings. It wasfound that sucrose suppressed the sour component of the sucrose/citricacid mixtures more than the salty component of the sucrose/sodiumchloride solutions This difference in component suppressionseemed to account for the hedonic integration patterns of thetwo mixture types which suggests that mixture suppression isan important factor to consider when predicting the pleasantnessof simple taste mixtures.