Evaluation of interaction in olfactory and taste mixtures

Models for the evaluation of interaction in olfactory and tastemixtures are compared to the isobole approach, which is widelyused in other fields of biomedical research. Analogies and differencesare described in detail. The isobole approach has a profoundtheoretical basis and can be applied to all possible types ofconcentration–response relationships, in particular toall values of exponents in the widely used power function, andeven if analytical expression of concentration–responserelationships are not known. Due to this generality it leadsto a substantial simplification of the evaluation proceduresas compared to other methods used in taste and olfaction research.It can be applied to any number of components of a mixture.Response surface modeling and computer graphics is recommededin appropriate cases because it can provide information on theconcentration dependence of interaction. Even though it hasto be pointed out that there is no general consensus on themost appropriate approach for the evaluation of interactionbetween biologically active agents so far, we are led to theconclusion that good arguments can be made in supporting theapplication of the isobole method for taste and olfactory mixtures.     

An assessment of binary mixture interactions for nine sweeteners

Binary mixtures of acesulfame K, aspartame, sodium cyclamate,fructose, glucose, stevioside, sodium saccharin, sucrose andxylitol were assessed using factorial mixture designs. A simpleadditive model was used to generate predictions for the sweetnessof the mixtures and these predicted responses were comparedto the observed sweetness ratings of the mixtures. It was foundthat the mixtures tended to exhibit superadditivity at low concentrations,additivity at intermediate concentrations and subadditivityat high concentrations. Synergistic and suppressive effectsin the mixtures were evaluated by comparing mixture responsesto the sweetness ratings of ‘self-mixtures’. Self-mixturedata were generated by treating a mixture of a substance withitself as if it were a mixture of two different substances.Synergism was defined as a mixture response that was greaterthan the sweetness of the component self-mixtures, and suppressionwas defined as a mixture response that was less than the sweetnessof the component self-mixtures. Of the 31 binary mixtures studied,18 showed synergism, two showed suppression and 11 did not differsignificantly from their components. It is hypothesized thatmultiple sweetness receptors or release from bitter suppressionmay account for the synergistic effects.     

Thermoreversible gelation of aqueous mixtures of pectin and chitosan. Rheology

The synergistic interaction between pectin and chitosan in aqueous acid solution and in the gel phase has been studied by oscillatory shear measurements. Mixtures of pectin and chitosan form thermoreversible gels over a broad composition range by lowering the temperature. The value of the gelation temperature depends on the composition of the mixture, with low values for mixtures with low pectin contents. For incipient gels, a power law can describe the frequency dependence of the complex viscosity, with power law exponents close to -1. The gel evolution of pectin-chitosan mixtures upon a temperature quench below the gel point has been studied. Evidence is provided for a relation between gelation and phase separation in the process of temperature-induced gelation of pectin-chitosan mixtures. A simple model is proposed to rationalize the gelation process in these systems.     

Concentration Addition,Independent Action and Generalized Concentration Addition Models for Mixture Effect Prediction of Sex Hormone Synthesis In Vitro

Humans are concomitantly exposed to numerous chemicals. An infinite number of combinations and doses thereof can be imagined. For toxicological risk assessment the mathematical prediction of mixture effects, using knowledge on single chemicals, is therefore desirable. We investigated pros and cons of the concentration addition (CA), independent action (IA) and generalized concentration addition (GCA) models. First we measured effects of single chemicals and mixtures thereof on steroid synthesis in H295R cells. Then single chemical data were applied to the models; predictions of mixture effects were calculated and compared to the experimental mixture data. Mixture 1 contained environmental chemicals adjusted in ratio according to human exposure levels. Mixture 2 was a potency adjusted mixture containing five pesticides. Prediction of testosterone effects coincided with the experimental Mixture 1 data. In contrast, antagonism was observed for effects of Mixture 2 on this hormone. The mixtures contained chemicals exerting only limited maximal effects. This hampered prediction by the CA and IA models, whereas the GCA model could be used to predict a full dose response curve. Regarding effects on progesterone and estradiol, some chemicals were having stimulatory effects whereas others had inhibitory effects. The three models were not applicable in this situation and no predictions could be performed. Finally, the expected contributions of single chemicals to the mixture effects were calculated. Prochloraz was the predominant but not sole driver of the mixtures, suggesting that one chemical alone was not responsible for the mixture effects. In conclusion, the GCA model seemed to be superior to the CA and IA models for the prediction of testosterone effects. A situation with chemicals exerting opposing effects, for which the models could not be applied, was identified. In addition, the data indicate that in non-potency adjusted mixtures the effects cannot always be accounted for by single chemicals.     

Solubility of the sodium salt of novobiocin in ethyl alcohol mixtures with other solvents]

Solubility of sodium novobiocin in binary mixtures of ethyl alcohol with ehtyl acetate, methylene chloride, diethyl ether, carbon tetrachloride or n-heptane was studied. Deviation in the sodium novobiocin solubility from the additivity was observed depending on the nature of the second component of the solvent mixture.     

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.     

Accession of sweet stimuli to receptors. I. Absolute dominance of one molecular species in binary mixtures

Intensity/time studies of sweetness response in pure solutions of each of nine different sweet stimuli have been carried out. Both variables exhibit simple power functions of the form Intensity (S) = kscns and Persistence (P) = kpcnp. In binary mixtures of these nine stimuli a depression (or negative synergism) of both sweetness intensity and persistence is observed which is predictable from the low exponents of the power functions. Combination of both power functions allows the "effective concentration" of each stimulus in a binary mixture to be calculated from its observed intensity/time characteristics. All "effective concentrations" calculable in this way show absolute dominance of one stimulus in mixtures of two irrespective of the relative proportions of the two stimuli. It is suggested that the "effective concentrations" may reflect real concentrations of a single molecular species in the microenvironment of the receptor. Thus the accession of sweet molecules to ordered, localized concentrations at the receptor is ultimately dependent on chemical structure.     

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.     

Selective inhibition of sweetness by the sodium salt of +/-2-(4-methoxyphenoxy)propanoic acid.

The purpose of this study was to determine the degree to which the sodium salt of +/-2-(4-methoxyphenoxy)propanoic acid (Na-PMP) reduced sweet intensity ratings of 15 sweeteners in mixtures. Na-PMP has been approved for use in confectionary/frostings, soft candy and snack products in the USA at concentrations up to 150 p.p.m. A trained panel evaluated the effect of Na-PMP on the intensity of the following 15 sweeteners: three sugars (fructose, glucose, sucrose), three terpenoid glycosides (monoammonium glycyrrhizinate, rebaudioside-A, stevioside), two dipeptide derivatives (alitame, aspartame), two N-sulfonylamides (acesulfame-K, sodium saccharin), two polyhydric alcohols (mannitol, sorbitol), 1 dihydrochalcone (neohesperidin dihydrochalcone), one protein (thaumatin) and one sulfamate (sodium cyclamate). Sweeteners were tested at concentrations isosweet with 2.5, 5, 7.5 and 10% sucrose in mixtures with two levels of Na-PMP: 250 and 500 p.p.m. In addition, the 15 sweeteners were tested either immediately or 30 s after a pre-rinse with 500 p.p.m. Na-PMP. In mixtures, Na-PMP at both the 250 and 500 p.p.m. levels significantly blocked sweetness intensity for 12 of the 15 sweeteners. However, when Na-PMP was mixed with three of the 15 sweeteners (monoammonium glycyrrhizinate, neohesperidin dihydrochalcone and thaumatin), there was little reduction in sweetness intensity. Pre-rinsing with Na-PMP both inhibited and enhanced sweetness with the greatest enhancements found for monoammonium glycyrrhizinate, neohesperidin dihydrochalcone and thaumatin, which were not suppressed by Na-PMP in mixtures. The mixture data suggest that Na-PMP is a selective competitive inhibitor of sweet taste. The finding that pre-treatment can produce enhancement may be due to sensitization of sweetener receptors by Na-PMP.     

The influence of sodium salts on binary mixtures of bitter-tasting compounds

In order to study potential mixture interactions among bitter compounds, selected sodium salts were added to five compounds presented either alone or as binary bitter-compound mixtures. Each compound was tested at a concentration that elicited 'weak' perceived bitterness. The bitter compounds were mixed at these concentrations to form a subset of possible binary mixtures. For comparison, the concentration of each solitary compound was doubled to measure bitterness inhibition at the higher intensity level elicited by the mixtures. The following sodium salts were tested for bitterness inhibition: 100 mM sodium chloride (salty), 100 mM sodium gluconate (salty), 100 and 20 mM monosodium glutamate (umami), and 50 mM adenosine monophosphate disodium salt (umami). Sucrose (sweet) was also employed as a bitterness suppressor. The sodium salts differentially suppressed the bitterness of compounds and their binary combinations. Although most bitter compounds were suppressed, the bitterness of tetralone was not suppressed, nor was the bitterness of the binary mixtures that contained it. In general, the percent suppression of binary mixtures of compounds was predicted by the average percent suppression of its two components. Within the constraints of the present study, the bitterness of mixtures was suppressed by sodium salts and sucrose independently, with few bitter interactions. This is consistent with observations that the bitter taste system integrates the bitterness of multi-compound solutions linearly.     

Interactions between oral chemical irritation, taste and temperature

The oral chemical irritant, capsaicin, at 2, 4 and 8 p.p.m.,was combined in mixtures with sucrose (Experiment 1), sodiumchloride (Experiment 2) and soup (Experiment 3), each evaluatedat two temperatures. These mixtures were rated for their sweetnessand/or saltiness, intensity of burning sensation and total mixtureintensity. In both solution and soup, sweetness was suppressed,whereas saltiness showed only minor suppression in low NaCl,high capsaicin mixtures. The burning sensation produced by capsaicinwas uninfluenced by sucrose, while NaCl increased the burningsensation. Total mixture intensity was entirely determined bycapsaicin concentration in mixtures with sucrose, although NaClcontributed in NaCl/capsaicin mixtures. Varying temperatureinfluenced the burning sensation and total intensity of sucrose/capsaicinmixtures, but did not modulate the effects of capsaicin on taste.Explanations of taste suppression in terms of cognitive andstructural models are examined. The differential effect of capsaicinon sweetness and saltiness is also considered in terms of theirritant properties of NaCl.     

The expected efficiencies of some methods of selection of components for inter-genotypic mixtures

Summary The gains in yields of mixtures expected to follow various methods of selection of components from populations of randomly constituted mixtures are formulated in terms of a statistical model and a model of first-order inter-plant competition. The types of selection investigated include that among whole mixtures and among groups or individual components on a within-mixture or unrestricted basis, or on the basis of the yields of sets of mixtures to which the group or individual is common. In all cases the sizes of mixture used for selection and for measurement of gain may differ. While evaluation of components in groups or whole mixtures allows selection for component interactions, gains are lower overall because of the reduction in variance caused by grouping. Gains due to interaction are lost if the components are pooled after selection, as in a population improvement programme. Individual selection carries some risk of negative gains, but these are reduced if assessment is made on an unrestricted rather than within-mixture basis. When second and higher order competitive interactions are absent, monoculture assessment is expected to be an efficient means of selection of components for binary and tertiary mixtures.     

Taste preference synergy between glutamate receptor agonists and inosine monophosphate in rats

Monosodium glutamate (MSG) elicits a taste called umami and interacts synergistically with nucleotide monophosphates such as 5'-inosine monophosphate (IMP) to potentiate this taste intensity. Indeed, the synergistic interaction of nucleotide monophosphates and MSG is a hallmark of umami. We examined interactions between MSG and other taste stimuli, including IMP, by measuring the lick rates of non-deprived rats during 30 s trials. To control for non-linear psychophysical functions, the concentration of one taste stimulus in a binary mixture was systematically increased while the concentration of the second taste stimulus was decreased (stimulus substitution method). Synergy between two stimuli was detected if the lick rate for a binary mixture exceeded that expected from the sum of the lick rates for each stimulus alone. In initial experiments, taste synergy was observed when rats were presented with mixtures of MSG and IMP but not with mixtures of MSG and sucrose. In subsequent experiments, glutamate receptor agonists other than MSG were presented with IMP to test for taste synergy. No evidence of synergy was seen when rats were presented with mixtures of IMP and kainic acid or IMP and N:-methyl-D-aspartate. However, taste synergy between IMP and L-AP4, a potent agonist at mGluR4 receptors, was observed. These results suggest that a metabotropic glutamate receptor similar to mGluR4 may be involved in the taste synergy that characterizes umami.     

Sensitivities of single nerve fibers in the hamster chorda tympani to mixtures of taste stimuli

Responses of three groups of neural fibers from the chorda tympani of the hamster to binary mixtures of taste stimuli applied to the tongue were analyzed. The groups displayed different sensitivities to six chemicals at concentrations that had approximately equal effects on the whole nerve. Sucrose-best fibers responded strongly only to sucrose and D-phenylalanine. NaCl-best and HCl-best fibers, responded to four electrolytes: equally to CaCl2 and nearly equally to HCl, but the former responded more to NaCl, and the latter responded more to NH4Cl. The groups of fibers dealt differently with binary mixtures. Sucrose- best fibers responded to a mixture of sucrose and D-phenylalanine as if one of the chemicals had been appropriately increased in concentration, but they responded to a mixture of either one and an electrolyte as if the concentration of sucrose or D-phenylalanine had been reduced. NaCl- best fibers responded to a mixture as if it were a "mixture" of two appropriate concentrations of one chemical, or somewhat less. But, responses of HCl-best fibers to mixtures were greater than that, approaching a sum of responses to components. These results explain effects on the whole nerve, suggest that the sensitivity of a mammalian taste receptor to one chemical can be affected by a second, which may or may not be a stimulus for that receptor, and suggest that some effects of taste mixtures in humans may be the result of peripheral processes.     

INTERACTION OF ASTRINGENCY AND TASTE CHARACTERISTICS1

The perception of astringency and basic taste in mixtures and their interaction effects were investigated by two procedures. In Experiment 1, focused and nonfocused testing procedures were compared using mixtures of low and high concentrations of alum and basic taste solutions. Both procedures yielded taste and astringency intensities that were modality‐dependent. Nonfocused testing was used in Experiment 2 to investigate the interactions of astringent phenolic (tannic acid) and nonphenolic (alum) compounds with each basic taste. Sweetness of sucrose increased with increased concentration with or without alum or tannin present. Changes in salty, bitter, and sour taste intensities were modality‐dependent. Astringency either remained unchanged or decreased with the addition of sucrose, sodium chloride, citric acid, or caffeine depending upon the taste concentration. Bitterness of tannin and alum at high concentrations was suppressed by the addition of sucrose, sodium chloride, or citric acid; sourness also decreased in the presence of sucrose or sodium chloride as well as a high level of caffeine.     

Heterogeneity in multistage carcinogenesis and mixture modeling

Carcinogenesis is commonly described as a multistage process, in which stem cells are transformed into cancer cells via a series of mutations. In this article, we consider extensions of the multistage carcinogenesis model by mixture modeling. This approach allows us to describe population heterogeneity in a biologically meaningful way. We focus on finite mixture models, for which we prove identifiability. These models are applied to human lung cancer data from several birth cohorts. Maximum likelihood estimation does not perform well in this application due to the heavy censoring in our data. We thus use analytic graduation instead. Very good fits are achieved for models that combine a small high risk group with a large group that is quasi immune.     

Some implications of a first-order model of inter-plant competition for the means and variances of complex mixtures

Summary Factorial models commonly used in the analysis of overall and component yields of binary mixtures of genotypes are generalised to include mixtures of any number of components (size, m) and the form of an analysis of variance for fitting such a model to tertiary mixtures is outlined. Such a model contains main effects and interactions up to the mth order, and is specific to the size of mixture so that no equivalence necessarily exists between similar parameter sets for different sized mixtures. Monocultures can be regarded as a special case of the general model.A simple model of intra-and inter-component competition is defined which assumes that plants do not interact in their competitive effects on others, a condition which is equivalent to an absence of second and higher order interactions in statistical analyses of mixtures of any size. Simple scaling tests involving the yields of components or whole mixtures of different sizes can also be used to test the adequacy of the model. This competition model least to a linear relationship between the mean yield of a mixture and the reciprocal of the number of components it contains, and thus allows the prediction of means and other statistical parameters for mixtures of one size from those of others.