Space and time separation of taste mixture components

Under natural conditions, all component qualities of taste mixturesco-exist in space and time on the tongue surface. The significanceof space-time coherence of taste sensations was investigatedby separating mixture components on the tongue. First, it wasshown that a mixture of sucrose plus sodium chloride is judgedto have a qualitatively different sweet taste from a mixtureof sucrose plus quinine sulphate when all taste qualities aretogether in space and time. This occurred even though mixtureswere matched for sweetness intensity, and the saltiness of theformer matched the bitterness of the latter. When, however,mixture components were spatially and temporally separated,the judged quality differences were eliminated. When the componentswere separated in space only, quality difference judgments werereduced in magnitude, but not eliminated. The results are consistentwith the hypothesis that space-time coherence of taste sensationsresult in perceptual blending and a consequent failure of selectiveattention to any single component. It is suggested that tastemixtures can be considered as single tastes even though componentqualities can be reliably identified using other techniques.     

Inheritance of taste components in tomato

Components of tomato taste can be modeled from a set of instrumentally measured parameters. The inheritance was studied of two texture parameters with an effect of mealiness and pleasantness of taste: BFp and EBp. A recombinant inbred line population (F6) of the cross tomato cv Moneymaker x L. pimpinellifolium was analyzed for these parameters, and a molecular linkage map was developed for this population. A single QTL region on chromosome 9 was found with an effect on both BFp and EBp. The QTL explained 18.2 and 18.8% of the population variances, and 19.5 and 39.0% of the parental differences respectively for BFp and EBp.     

Successive contrast cannot explain suppression release after repetitious exposure to one of the components of a taste mixture

Repetitious exposure to one of the components of a NcCl-sucrosemixture causes the other component to recover from suppression.This so-called‘suppression release’ might be explainedby assuming that the subjects habituate to the repeated component,which is thereby disabled as a suppressor in the mixture. Twoexperiments are reported that test successive contrast as analternative explanation of this type of suppression release.This alternative was investigated by substituting an unmixedtest stimulus of about equal subjective sweetness (or saltiness)for the mixture. The results indicate that successive contrastcontributes only partially to the suppression-release effect.When the contrast contribution is subtracted, a significantsuppression-release effect remains.     

Temporal properties of the human taste system.

An attempt to apply linear systems methods to the temporal properties of the human taste system is described. The percentage modulation in concentration required to detect a fluctuation in intensity was measured as a function of frequency of modulation. Both a sine-wave and a square-wave input were used. The sensitivity of the taste system at its maximum, and also at the low frequencies, was greater than expected from previous work based on classical methodology. The sensitivity of the taste system at its maximum, and also at the low frequencies, was greater then expected from previous work base on classical methodology. The sensitivity of the taste system to the various qualities was, in decreasing order, salty, sweet, sour, and bitter. The taste system in insensitive to frequencies above about 5 Hz. Except for bitter, representatives of the various taste qualities yielded similar functions within qualities.     

Temporal synchrony and integration of sub-threshold taste and smell signals

The importance of stimulus timing and location on the perceptual integration of taste and odour was studied based on a sub-threshold methodology. From a panel of 16 people, 12 showed the integration effect previously reported while 4 showed no effect. The experiment was repeated using retronasal and orthonasal delivery of the odour and with tastant present or absent in the mouth. Integration of taste and odour only occurred when both stimuli were present at the same time. Retro- or orthonasal presentation both produced integration providing that tastant delivery was synchronous but the threshold values for the two presentation methods were different. The relevance of these findings to flavour perception under realistic conditions is considered.     

Temporal changes in NCAM immunoreactivity during taste cell differentiation and cell lineage relationships in taste buds

Neural cell adhesion molecule (NCAM) is a type III cell marker in the taste buds. In order to clarify the cell type of Mash1-expressing cells in taste buds, expression of NCAM was examined in Mash1-expressing taste cells of adult mice in comparison with gustducin- and T1r3-expressing cells, using a combination of NCAM immunohistochemistry and in situ hybridization. About 98% of Mash1-expressing cells were NCAM immunopositive (IP), suggesting that Mash1-expressing cells should be categorized as type III cells. Unexpectedly, small subsets of gustducin- and T1r3-expressing cells were also found to be NCAM-IP, contradicting previous immunohistochemical studies in rats, in which gustducin-IP cells were observed specifically in type II cells, which do not have NCAM immunoreactivity. Examinations of developing taste buds showed temporal changes in the ratio of NCAM-IP cells in gustducin- and T1r3-expressing cells; the ratio of NCAM-IP cells in these gene-expressing cells were approximately 90% at 0.5 days after birth and decreased markedly during development. In contrast, the majority of Mash1-expressing cells showed constant NCAM immunoreactivity throughout development. In addition, BrdU-labeling experiments showed that the differentiation of Mash1-expressing cells precedes those of gustducin- and T1r3-expressing cells in taste buds of adult mice. These results suggest that T1r3- and gustducin-expressing cells are NCAM-IP at the beginning of cell differentiation, and that NCAM immunoreactivity in gustducin- and T1r3-expressing cells might remain from the previous developmental stage expressing Mash1.     

Temporal separation of two components of phytochrome action

Abstract In germinating seedlings of Sinapis alba nitrate reductase activity as assayed in vivo becomes accessible to phytochrome control between 15 and 17 h after sowing. Phytochrome operates via the high irradiance reaction to control nitrate reductase activity in the period 15 to 20 h after sowing. Both continuous red light and far-red light elicit this response with a strong fluence rate dependency being apparent in each case. The induction of nitrate reductase activity by light pulses at 20 h after sowing is greatly influenced by red light pre-treatments (operating through phytochrome) given between 0 and 15 h after sowing. Low fluence rate pre-treatments reduce the effectiveness of a subsequent pulse to below the level of a dark control whilst high fluence rate pre-treatments greatly increase the effectiveness of a subsequent pulse.     

Binary taste mixture interactions in prop non-tasters, medium-tasters and super-tasters

It is generally assumed that the mutual, but asymmetric, suppression of the components in binary taste mixtures is an invariant property of the human psychophysical response to such mixtures. However, taste intensities have been shown to vary as a function of individual differences in sensitivity, indexed by the perceived bitterness of 6-n-propylthiouracil (PROP). To determine if these variations in taste perception influence taste mixture interactions, groups of PROP super-, medium- and non-tasters assessed four binary taste mixtures: sweet-bitter [sucrose/quinine hydrochloride (QHCl)], sweet-sour (sucrose/citric acid), salty-bitter (NaCl/QHCl) and salty-sour (NaCl/citric acid). In each experiment, subjects received factorial combinations of four levels of each of two tastants and rated individual taste intensities and overall mixture intensity. For each taste quality, super-tasters typically gave higher ratings than either medium- or non-tasters, who tended not to differ. There were also group differences in the interactions of the mixtures' components. Super-tasters rated the overall intensity of the mixtures, most likely reflecting integration of the taste components, as greater than medium- and non-tasters, who again showed few differences. In sweet-bitter mixtures, non-tasters failed to show the suppression of sweetness intensity by the highest QHCl concentration that was evident in super- and medium-tasters. These data show that the perception of both tastes and binary taste mixture interactions varies as a function of PROP taster status, but that this may only be evident when three taster groups are clearly distinguished from one another.     

The validity of the equiratio taste mixture model investigated with sorbitol-sucrose mixtures

The equiratio taste mixture model developed and shown to bevalid for glucose-fructose mixtures was investigated in orderto assess its applicability to two-component mixtures of othersweet substances. A magnitude estimation experiment using thesip and spit procedure determined psychophysical functions forsorbitol, sucrose and three equiratio sorbitol-sucrose mixtures.Mixture functions determined on the basis of the experimentaldata were very similar to those predicted by the model. Thepsychophysical functions for sucrose and the sorbitol-sucrosemixtures showed slight downward curvature. As these deviationsfrom the power law affect the predictive validity of the model,potential factors causing these curvatures are discussed.     

Sensory evaluation of character impact components in an apple model mixture

Food aromas generally are complex mixtures of volatiles. In the present study, we investigated the joint effects of hexyl acetate, trans-2-hexenal and 1-hexanol on the multi-attribute perception of an apple aroma. The first two substances were identified earlier as positive contributors to the apple aroma (high character impact), whereas the third component was identified as an irrelevant or negative contributor (low character impact). Aroma quality was quantified using a set of eight graphic rating scales. All three components had significant effects on the aroma profiles. These effects consist mainly of an effect of each component on the attribute that described its individual character and an effect of all three components on ratings on the main character attribute 'apple'. As expected, the high impact components increased 'apple' ratings, whereas the low character impact component decreased 'apple' ratings. Furthermore, intensity ratings on the attribute that corresponded with the odour of the low impact component were suppressed by the presence of high impact components. These results indicate that the contributions of odorants to the mixture's aroma are not linear combinations of separate odour intensities, because sensory interactions were observed. In addition, humans detect components in complex mixtures more accurately than studies on identification performance have suggested. We conclude that for an adequate assessment of the effects of multiple mixture components on changes in aroma perception, it is sufficient to employ multiple response scales measuring intensities of attributes that are distinctive with respect to the expected qualitative changes. Results of this approach should be subjected to multivariate methods of statistical analysis.     

Retention of components in a mixture of volatile organic substances by maltodextrins

The effect of composition and origin of maltodextrins on the retention of 38 components in a mixture of volatile organic substances (odorants) during 6-month storage was studied by means of capillary gas-liquid chromatography. The retention of esters increased with an increase in their molecular weight. The retention of lactones, phenols, linalool, menthone, and damascone was 75–85%. Storage of aldehydes was accompanied by oxidation, and the retention of these substances did not exceed 55%. The retention of odorants increased with a decrease in the molecular weight of maltodextrins. The maximum retention was typical of maltodextrin from amylopectin starch not containing amylose.     

Sorption of components from a mixture of essential oils by cryotextured cornstarches

Sorption by cryotextured cornstarches of components of the aqueous phase of a mixture of essential oils was studied by capillary gas chromatography. The amount of cryotexture-sorbed substances depended linearly on their concentration in the initial gel. The sorption of components from the mixture by starch polysaccharides was mainly associated with hydrophobic cooperative interactions, which resulted in the formation of supramolecular structures and inclusion complexes. The structure of the compounds was a major factor determining the degree of sorption. Sorption of monoterpene carbohydrates was the most pronounced. We revealed a synergistic increase in the degree of sorption from the mixture as compared to binding of individual compounds.     

Retention of components in a mixture of volatile organic substances by maltodextrins

The effect of composition and origin of maltodextrins on the retention of 38 components in a mixture of volatile organic substances (odorants) during 6-month storage was studied by means of capillary gas-liquid chromatography. The retention of esters increased with an increase in their molecular weight. The retention of lactones, phenols, linalool, menthone, and damascone was 75-85%. Storage of aldehydes was accompanied by oxidation, and the retention of these substances did not exceed 55%. The retention of odorants increased with a decrease in the molecular weight of maltodextrins. The maximum retention was typical of maltodextrin from amylopectin starch not containing amylose.     

A mixture model with random-effects components for clustering correlated gene-expression profiles

MOTIVATION: The clustering of gene profiles across some experimental conditions of interest contributes significantly to the elucidation of unknown gene function, the validation of gene discoveries and the interpretation of biological processes. However, this clustering problem is not straightforward as the profiles of the genes are not all independently distributed and the expression levels may have been obtained from an experimental design involving replicated arrays. Ignoring the dependence between the gene profiles and the structure of the replicated data can result in important sources of variability in the experiments being overlooked in the analysis, with the consequent possibility of misleading inferences being made. We propose a random-effects model that provides a unified approach to the clustering of genes with correlated expression levels measured in a wide variety of experimental situations. Our model is an extension of the normal mixture model to account for the correlations between the gene profiles and to enable covariate information to be incorporated into the clustering process. Hence the model is applicable to longitudinal studies with or without replication, for example, time-course experiments by using time as a covariate, and to cross-sectional experiments by using categorical covariates to represent the different experimental classes. RESULTS: We show that our random-effects model can be fitted by maximum likelihood via the EM algorithm for which the E(expectation)and M(maximization) steps can be implemented in closed form. Hence our model can be fitted deterministically without the need for time-consuming Monte Carlo approximations. The effectiveness of our model-based procedure for the clustering of correlated gene profiles is demonstrated on three real datasets, representing typical microarray experimental designs, covering time-course, repeated-measurement and cross-sectional data. In these examples, relevant clusters of the genes are obtained, which are supported by existing gene-function annotation. A synthetic dataset is considered too. AVAILABILITY: A Fortran program blue called EMMIX-WIRE (EM-based MIXture analysis WIth Random Effects) is available on request from the corresponding author.     

Temporal and mechanistic dissociation of ATP and adenosine release during ischaemia in the mammalian hippocampus

Adenosine is well known to be released during cerebral metabolic stress and is believed to be neuroprotective. ATP release under similar circumstances has been much less studied. We have now used biosensors to measure and compare in real time the release of ATP and adenosine during in vitro ischaemia in hippocampal slices. ATP release only occurred following the anoxic depolarisation, whereas adenosine release was apparent almost immediately after the onset of ischaemia. ATP release required extracellular Ca2+. By contrast adenosine release was enhanced by removal of extracellular Ca2+, whilst TTX had no effect on either ATP release or adenosine release. Blockade of ionotropic glutamate receptors substantially enhanced ATP release, but had only a modest effect on adenosine release. Carbenoxolone, an inhibitor of gap junction hemichannels, also greatly enhanced ischaemic ATP release, but had little effect on adenosine release. The ecto-ATPase inhibitor ARL 67156, whilst modestly enhancing the ATP signal detected during ischaemia, had no effect on adenosine release. Adenosine release during ischaemia was reduced by pretreatment with homosysteine thiolactone suggesting an intracellular origin. Adenosine transport inhibitors did not inhibit adenosine release, but instead they caused a twofold increase of release. Our data suggest that ATP and adenosine release during ischaemia are for the most part independent processes with distinct underlying mechanisms. These two purines will consequently confer temporally distinct influences on neuronal and glial function in the ischaemic brain.     

Responsiveness of the cortical taste area neurons to a mixture of the four basic tastants in rats

The taste coding mechanism in the cortical taste area was investigated by analyzing the responses of 59 neurons in the cortical taste area of the anesthetized rat to a mixture of the four basic tastants in both absence and presence of bicuculline methiodide, a specific antagonist to the GABA(A) receptors. The mixture caused response suppression more frequently than response facilitation, both in the control state and during bicuculline application. Cluster analysis revealed that only a group of the neurons with the best response to both NaCl and HCl (group NH) showed the best response to the mixture in the control state, whereas during bicuculline application, in addition to group NH, two other groups of neurons responding to sucrose, or to HCl and quinine responded vigorously to the mixture. Multidimensional scaling located the mixture outside the space of the four basic tastants facing an NaCl-HCl line in both states. GABAergic inhibition caused the group NH to represent the taste of the mixture in the control state. Thus, the mixture probably tastes salty and sour to rats. No cortical neuron was found which specifically responded to the mixture.