A COMPARISON OF METHODOLOGY APPLIED TO THE SELECTION OF A PANEL FOR SENSORY EVALUATION OF INSTANT COFFEE

Twenty judges performed a variety of chemosensory tasks in order to select the best scores to form a panel for coffee evaluation. An average of correct responses (P%), one-way analysis of variance (ANOVA) and principal components analysis (PCA) were compared. The tests involved: ability to recognize the four basic tastes, identification and matching of odors, taste intensity evaluation and perception of small differences in taste. P% accounted for 71.17 ± 4.34% and 10 of the judges had scores greater than the final average. ANOVA and PCA resulted in 2 different panels consisting of 9 and 12 judges, respectively. The panel was composed by the nine panelists selected by the three methods. The other three panelists that were doubtful could improve to the point of acceptance with additional training. These methods should be used simultaneously to have more security in the acceptance or rejection of panelists.     

Cross-adaptation and bitterness inhibition of L-tryptophan, L-phenylalanine and urea: further support for shared peripheral physiology

A previous study investigating individuals' bitterness sensitivities found a close association among three compounds: L-tryptophan (L-trp), L-phenylalanine (L-phe) and urea (Delwiche et al., 2001, Percept. Psychophys. 63, 761-776). In the present experiment, psychophysical cross-adaptation and bitterness inhibition experiments were performed on these three compounds to determine whether the bitterness could be differentially affected by either technique. If the two experimental approaches failed to differentiate L-trp, L-phe and urea's bitterness, then we may infer they share peripheral physiological mechanisms involved in bitter taste. All compounds were intensity matched in each of 13 subjects, so the judgments of adaptation or bitterness inhibition would be based on equal initial magnitudes and, therefore, directly comparable. In the first experiment, cross-adaptation of bitterness between the amino acids was high (>80%) and reciprocal. Urea and quinine-HCl (control) did not cross-adapt with the amino acids symmetrically. In a second experiment, the sodium salts, NaCl and Na gluconate, did not differentially inhibit the bitterness of L-trp, L-phe and urea, but the control compound, MgSO(4), was differentially affected. The bitter inhibition experiment supports the hypothesis that L-trp, L-phe and urea share peripheral bitter taste mechanisms, while the adaptation experiment revealed subtle differences between urea and the amino acids indicating that urea and the amino acids activate only partially overlapping bitter taste mechanisms.     

THE EFFECT OF MASTICATORY PATTERNS AS MEASURED BY TIME-INTENSITY AND ELECTROMYOGRAPHY ON THE PERCEPTION OF BOVINE MUSCLE TENDERNESS

The relationship between perception of tenderness and chewing activity was explored using the Time-Intensity measurement of perception and electromyographic measurements of masseter muscle movement. Semitendinosus muscles from eight treatments of forage fed beef were evaluated by nine individuals. The Time-Intensity parameters of Area Under the Curve and Decrease Area were the most useful for treatment separation based on tenderness. Information was obtained from the electromyogram regarding the number of chews, time to chew and mastication rate. However, more work with EMG measurements is required to accurately study the effect of masticatory patterns on tenderness perception.     

EVALUATION OF WINE COMPETITION JUDGE PERFORMANCE USING PRINCIPAL COMPONENT SIMILARITY ANALYSIS

Principal component similarity (PCS) analysis was used to evaluate judge performance from a wine competition. Data were analyzed for five international judges and seven wine makers, for 42 white, 30 red and 25 specialty wines, using a 20-point quality scoring system. Principal similarity plots were used to group judges according to judging 'style' and to identify outliers, for each wine category. Judge groupings were consistent when three different references were used; however, the most interpretable PCS plot was obtained when the overall mean-judge-score was used as the reference. Results from PCS were compared to principal component analysis (PCA). PCS analysis allowed the information from all significant principal components to be graphically represented in two dimensions and was more successful in classifying judges than plots based on the first three principal components. The technique of PCS is an important complement to existing methodologies, and can provide wine competition coordinators with an objective technique for judge evaluation and selection.     

FRESHNESS IN ORAL CARE: ATTRIBUTES AND TIME-DEPENDENCY OF A MULTIDIMENSIONAL, DYNAMIC CONCEPT

This article describes an exploration of the concept of 'oral freshness' for as far as it is important in oral care. It intends to consider the most important mouth sensations and cognitive connotations, including (but not restricted to) the well-known effect of menthol in toothpaste.
Two aspects were given attention:
(1) The attributes that together form the concept of oral freshness were investigated using a 'personal construct approach'(Kelly 1955). This method consists of unbiased, structured interviews with subjects, and ultimately yields attribute dimensions that the subjects have in common.
(2) The intensity of the freshness sensation over time was investigated using the Time-Intensity method. Subjects gave repeated freshness judgments every few seconds after the intake of a freshness-related stimulus, and continued to do so after the stimulus had left their mouth. In addition we asked for 'overall' freshness judgments directly after the TI-measurements and after 2 months.
The results confirm that 'oral freshness' is a complex concept. We identified 6 attributes, some of which were perceptual/physiological and some cognitive in nature: 'water'-ness, cool/cold-ness, taste (menthol-ness), clean-ness, smell, energy (texture and touch, e.g., bubbles). Different persons will generally give different importance weights to each of these 6 attributes.
Time-intensity measurements show that temperature, menthol-content and, to some extent, the presence of bubbles (energy) influence the momentous sensation of freshness. It appears, however, that in the way freshness is remembered after a few months, mainly cleanness and taste (menthol-ness) are important. Apparently, people tend to value (temporary) sensory input during the actual freshness experience, but tend to remember the freshness result in the longer run.     

SENSORY ADAPTATION

Sensory evaluation makes use of the remarkable virtuosity and range of the human senses as a multi-purpose instrument for measuring the sensory characteristics of foods. The brain protects itself from an overload of information from the senses by two processes: feature extraction and adaptation. The former involves information reduction by the extraction of selected features from the environment; these form the basis for the reconstruction of the percept in consciousness. The latter, adaptation, involves the attenuation of repetitive and constant input so as not to overload the brain with redundant information.
The effects of adaptation can be observed for all senses. For the chemical senses, the effect is that a constant odor or taste stimulus will be perceived as decreasing in intensity while sensitivity to that stimulus is also decreased. For sensory evaluation, this poses problems. It means that a taste or odor has a tendency to vanish while it is being observed and that sensitivity to subsequent stimuli will be altered. Such sensitivity drift in the human instrument must be anticipated in the design of measurement procedures for the sensory evaluation of food.
For taste, adaptation changes caused by the measurement method can be seen to be largely responsible for disagreements in the literature concerning threshold and intensity measurement. Adaptation is also a contributing factor, but by no means the only one, in determining the relative discriminability of sensory difference tests. It is worth noting, however, that adaptation is not always a disadvantage; it can sometimes be used to advantage in sensory testing procedures.     

The independence and integration of olfaction and taste

To study the influences of smell on the scaling of taste, andvice versa, an unobtrusive device was developed which permitsthe independent varying of the olfactory and gustatory componentsof a flavor compound. With instant coffee and the method ofmagnitude estimation, the slopes of the olfactory, taste, andflavor curves produced by this device were similar to thoseproduced by more traditional delivery systems. To study theinteraction of taste on smell and vice versa, subjects scaledolfactory stimuli against different taste backgrounds and tastestimuli against different odorant backgrounds. Taste backgroundsdid not significantly alter the scaling of olfaction. Similarly,olfactory backgrounds did not significantly alter the scalingof taste. Finally, subjects scaled overall intensity (flavor)when presented with all combinations of four concentrationsof odorants and tastants. Smell and taste were shown to contributeindependently to the estimation of overall intensity.     

Contributions of Smell and taste to overall intensity

The integration of olfaction and gustation in producing thesensation of flavor was studied using an almond extract stimuluspresented with the Two-Module Delivery System. Almond in themouth was found to influence the scaling of smell. The datasugest that this background effect is due to the diffusion ofairborne molecules from the oral cavity to the olfactory receptorsarea. At least under some stimulation conditons, almond vaporin the nose was shown to afect the scaling of taste. When scalingoverall intensity, subjects apparently added together the sensationsof smell and taste to produce the sensation of overall intensity.However, for all combinations of odorants and tastants, theestimate of overall intensity was less than the sum of the estimateof the smell and the estimate of the taste. The data furthersuggest that when estimating the overall intensity, the magnitudeassigned to the olfactory or gustatory sensations was less thanthat which have been assigned when estimating just smell ortaste.     

The Perception of Saltiness is Eliminated by NaCl Adaptation: Implications for Gustatory Transduction and Coding

The tastes of salts to humans are complex. NaCl is the mostpurely salty of all salts, but even this stimulus tastes sweetat low concentrations and somewhat sour at mid-range intensities.Other salts taste significantly sour or bitter in addition tosalty. Previous studies have shown that the saltiness of simplehalide salts is reduced by adaptation to NaCl, suggesting thata single mechanism might be responsible for the salty tasteof these stimuli. In electrophysiological studies in rodents,the response to NaCl is reduced by application to the tongueof the Na⁺- channel blocker amiloride. Organic Na⁺ salts aremore heavily dependent on this amiloride-sensitive transductioncomponent than NaCl, and are generally less salty and more sour.In order to investigate the relationship between NaCl saltinessand that evoked by other salts, we adapted the tongue to distilledH₂O and to 0.1 M NaCl and obtained direct magnitude estimatesof the taste intensity of 15 organic and inorganic Na⁺, Li⁺,K⁺ and Ca²⁺ salts, matched for total intensity. Subjects dividedthese magnitude estimates among the component taste qualities.Adaptation to NaCl abolished the taste of NaCl and LiCl, andeliminated the saltiness of all other salts. The magnitude estimatesof the bitterness and sourness of many salts increased afterNaCI adaptation. Since recent biophysical data suggest thatadaptation in taste receptors may involve whole-cell mechanisms,we propose that saltiness is reduced by NaCl adaptation becauseit originates in the subset of taste receptors responsive toNaCl. This implies that saltiness is coded within the CNS incells whose receptive fields include the NaCl-sensitive receptorcells and that the degree to which any salt tastes salty isdetermined by its ability to drive these receptors. This modelproposes, for example, that KCl has a salty component becauseit stimulates some of the same receptor cells as NaCl, eventhough the transduction mechanisms for KCl are different thanthose engaged by NaCl. Adaptation to NaCl blocks the saltinessof KCl and other salts because they stimulate NaCl-sensitivereceptor cells. Chem. Senses 20: 545–557, 1995.     

The addition of CO2 to traditional taste solutions alters taste quality

Previous studies of the effect of carbonation on taste perception have suggested that it may be negligible, manifesting primarily in increases in the perceived intensity of weak salt and sour stimuli. Assuming CO2 solutions in the mouth stimulate only trigeminal nerve endings, this result is not altogether surprising; however, there are neurophysiological data indicating that CO2 stimulates gustatory as well as trigeminal fibers. In that case, carbonation might alter the quality profile of a stimulus without producing substantial changes in overall taste intensity--much as occurs when qualitatively different taste stimuli are mixed. To address this possibility, subjects were asked to rate the total taste intensity of moderate concentrations of stimuli representing each of the basic tastes and their binary combinations, with an without added carbonation. They then subdivided total taste intensity into the proportions of sweetness, saltiness, sourness, bitterness and 'other taste qualities' they perceived. The addition of carbonation produced only small increases in ratings of total taste intensity. However, rather dramatic alterations in the quality profiles of stimuli were observed, particularly for sweet and salty tastes. The nature of the interaction is consistent with a direct effect of carbonation/CO2 on the gustatory system, although the possibility that at least some of the observed effects reflect trigeminal-gustatory interactions cannot be ruled out.      

Electrical taste stimulus: current intensity or current density?

In electrical taste stimulation, current intensity is usuallyconsidered to be a simple equivalent of the taste stimulus intensity,this being analogous to the concentration of a chemical solution.However, there are indications that current density might bea better correlate of the true electrical taste stimulus. Inthe present study the relationship between the size of the stimulatedhuman tongue area, the electrical current intensity, and themagnitude of elicited taste sensations was examined. Tests insix subjects showed that in order to achieve the standard sourtaste magnitude when using electrode sizes that increased insize, the current intensity also had to be increased, but currentdensity decreased. This might be attributed to spatial summationwhich is plausible only if current density was taken as a realelectrical taste stimulus. Summation degree was less than complete,indicating that the density might be a predominant, but notthe only factor in electrical stimulus efficacy.     

The Effect of Adaptation on the Taste Threshold Observed with a Semiautomatic Gustometer

A special "gustometer" has been built, which permits continuous measurement of the threshold of taste sensations. Taste sensations show strong adaptation even at the threshold level. The adaptation was much the same for the four primary tastes, but there were large individual differences. Of theoretical interest is the finding that adaptation to a taste can occur even with subliminal stimuli.     

Oral chemical irritation: does it reduce perceived taste intensity?

In an experiment in which capsaicin was presented in physicalmixture with taste stimuli, no reduction in perceived tasteintensity, relative to the control condition, was observed.This result is inconsistent with previous reports of taste intensityreductions when oral chemical irritants were only periodicallyinterspersed among taste stimuli (Lawless et al., 1985; Lawlessand Stevens, 1984). A second experiment directly compared thetwo presentation formats and their respective control conditionsin a repeated-measures design. The results of that test confirmthat greater apparent reductions in taste intensity are observedwhen the oral irritant is presented as a periodic rinse eventhough perceived irritation under rinse conditions regularlyfalls to levels significantly below those maintained with mixturepresentations. This observation indicates that much of the apparentmasking of taste intensity in the presence of oral irritationis not directly related to irritation level but is sensitiveto procedural variation.     

Reduction of saltiness and bitterness after a chlorhexidine rinse

Chronic rinsing with chlorhexidine, an oral-antiseptic, has been shown to decrease the saltiness of NaCl and the bitterness of quinine. The effect of acute chlorhexidine on taste has not been investigated. The purpose of the present study was to examine the effect of acute chlorhexidine rinses on taste intensity and quality of 11 stimuli representing sweet, salt, sour, bitter and savory. All stimuli were first matched for overall intensity so the effects of chlorhexidine would be directly comparable across compounds. As a control treatment, the bitter taste of chlorhexidine digluconate (0.12%) was matched in intensity to quinine HCl, which was found to cross-adapt the bitterness of chlorhexidine. Subjects participated in four experimental conditions: a pre-test, a quinine treatment, a chlorhexidine treatment, and a post-test condition, while rating total taste intensity and taste qualities in separate test sessions. Relative to the quinine treatment, chlorhexidine was found to decrease the salty taste of NaCl, KCl and NH4Cl, and not to significantly affect the tastes of sucrose, monosodium glutamate (MSG), citric acid, HCl and the taste of water. The bitter taste of urea, sucrose octa-acetate and quinine were suppressed after chlorhexidine rinses relative to water rinses, but were only marginally suppressed relative to quinine rinses. Potential mechanisms are discussed.     

Local Adaptation of Bitter Taste and Ecological Speciation in a Wild Mammal

Sensory systems are attractive evolutionary models to address how organisms adapt to local environments that can cause ecological speciation. However, tests of these evolutionary models have focused on visual, auditory, and olfactory senses. Here, we show local adaptation of bitter taste receptor genes in two neighboring populations of a wild mammal—the blind mole rat Spalax galili—that show ecological speciation in divergent soil environments. We found that basalt-type bitter receptors showed higher response intensity and sensitivity compared with chalk-type ones using both genetic and cell-based functional analyses. Such functional changes could help animals adapted to basalt soil select plants with less bitterness from diverse local foods, whereas a weaker reception to bitter taste may allow consumption of a greater range of plants for animals inhabiting chalk soil with a scarcity of food supply. Our study shows divergent selection on food resources through local adaptation of bitter receptors, and suggests that taste plays an important yet underappreciated role in speciation.     

Tactile interaction with taste localization: influence of gustatory quality and intensity

Taste is always accompanied by tactile stimulation, but little is known about how touch interacts with taste. One exception is evidence that taste can be "referred" to nearby tactile stimulation. It was recently found (Lim J, and Green BG. 2007. The psychophysical relationship between bitter taste and burning sensation: evidence of qualitative similarity. Chem Senses. 32:31-39) that spatial discrimination of taste was poorer for bitterness than for other tastes when the perceived intensities were matched. We hypothesized that this difference may have been caused by greater referral of bitterness by touch. The present study tested this hypothesis by comparing localization of quinine sulfate and sucrose under conditions that minimized and maximized the opportunity for referral. In both conditions, stimulation was produced by 5 cotton swabs spaced 1 cm apart and arranged in an arc to enable simultaneous contact with the front edge of the tongue. Only one swab contained the taste stimulus, whereas the rest were saturated with deionized water. In both conditions, the swabs were stroked up-and-down against the tongue 5 times. Subjects were asked to identify which swab contained the taste stimulus 1) 5 s after the fifth stroke (touch-removed condition) and 2) immediately at the end of the fifth stroke, with the swabs still in contact with the tongue (touch-maintained condition). Ratings of taste intensity were obtained to assess the possible effect of perceived intensity on spatial localization. Taste localization was surprisingly accurate, especially for sucrose, with errors of localization in the range of 1 cm or less. For both stimuli, localization tended to be poorer when the tactile stimulus was present while subjects made their judgments, but the difference between conditions was significant only for the lower concentration of quinine. The results are discussed in terms of both the surprisingly good spatial acuity of taste and the possibility of having a close perceptual relationship between touch and bitter taste.