TASTE THRESHOLDS, TASTE SENSITIVITY AND THE EFFECTS OF ADRENALECTOMY IN RATS

A number of behavioral experiments have attempted to measurethe absolute taste thresholds in the rat. Certain aspects ofthe procedures and methods of data analysis used in these experimentsare reviewed with the suggestions that: (1) Although comparisonshave commonly been made between the taste threshold values reportedin different experiments, these are not valid because of theabsence of a common definition of threshold. (2) The high thresholdmodel on which these experiments are based may be inappropriate.(3) It is possible to measure taste sensitivity rather thantaste thresholds, and (4) Had these points been considered inprevious experiments different conclusions might have resultedregarding the effects of adrenalectomy on NaCl sensitivity.     

COMPARISON OF SIMPLIFIED METHODS FOR EVALUATION OF SENSORY THRESHOLDS OF ADDED SUBSTANCES

Results obtained in the determination of sensory thresholds with three different simplified methods were compared. The methods were: a modification of the ascending method of limits (1), one based on the method of the constant stimuli (2), and one based on the use of scales (3). The study was carried out on two sensorially simple systems, sucrose and aspartame aqueous solutions. The thresholds values for sucrose obtained by method 1 (1.41 g/L) and by method 2 (1.60 g/L) were similar and within the range obtained by method 3 (0.6–1.6 g/L). For aspartame the values obtained with methods 1 and 2 were also similar (0.004 and 0.005 g/L, respectively), but they were below the minimum value of the corresponding range (0.008–0.016 g/L) calculated with method 3. These results suggest that the sensory methods provoked less variability in thresholds values than other noncontrolled factors. The limitations and advantages of each method are discussed considering: experimental work, precision of results and practical validity.     

SENSORY THRESHOLDS: CONCEPTS AND METHODS

A sensory threshold can be defined generally as a stimulus intensity that produces a response in half of the trials. The definition of the population threshold is discussed. Five main classical statistical procedures for estimating thresholds are reviewed. They are the probit, the logistic, the Spearman-Karber, the moving average and the up-and-down procedures. Some new developments in statistical methods for estimating thresholds are outlined. The newly developed methods include the generalized probit and logistic models, the model based on the Beta-Binomial distribution, the trimmed Spearman-Karber method, the kernel method and the sigmoidally constrained maximum likelihood estimation method. The authors propose a new procedure based on the Beta-Binomial distribution for estimating population threshold.     

SENSORY EVALUATION OF IRRADIATED BEEF AND BACON

Vacuum-packed beef and bacon were treated with gamma- radiation (1–10 KGy) from CO⁶⁰ and stored for 3 months at + 4°C. The samples were evaluated by a trained sensory laboratory panel, directly after irradiation, and after 3 months. Samples given 1.0 KGy and higher doses were found to be significant different from nonirradiated samples at both times of testing. A higher intensity of off-taste, rancidity, metallic taste and sweetness, and a lower intensity of juiciness and color saturation were found in all the irradiated samples. Off-taste and rancidity were found to increase with increasing doses, and were best explained when analyzed by Principal Component Analysis (PCA).     

SENSORY AND INSTRUMENTAL EVALUATION OF STRAWBERRY YOGURT COLOR

Eleven samples of strawberry yogurt prepared with different red color concentrations using Ponceau 4R (E-124) were evaluated by instrumental and sensory methods. Color intensity evaluation was carried out by a panel of eight assessors specifically trained to measure strawberry color in yogurt. Color acceptability was measured with 120 regular and frequent consumers of yogurt. Color was measured with a Minolta Chroma Meter CR-200b, obtaining parameters L*, a* and b*. Principal component analysis was performed on the instrumental variables. Regression models between the instrumental first principal component, red color concentration, sensory intensity, and acceptability allowed determining quality control limits for red color attribute. These limits may be controlled by selecting either instrumental or sensory methods, being the latter easy to implement and providing dependable results.     

EVALUATION OF RANGE-GRAZED AND CONCENTRATE-FEDBEEF BY A TRAINED SENSORY PANEL, A HOUSEHOLD PANEL AND A LABORATORY TEST MARKET GROUP

A trained sensory panel and a household panel evaluated leaner range-grazed and higher grading concentrate-fed beef for sensory characteristics. The findings were compared to those from a laboratory test market study designed to determine the consumer appeal of branded range-grazed beef when compared to concentrate-fed beef. Broiled steaks from concentrate-fed steers were scored more flavorful, more tender, more juicy and more desirable overall than those from range-grazed steers by the trained sensory panel and by the household panel. In the laboratory test market study steaks from range-grazed steers were nearly equal in acceptance to those from concentrate-fed steers because consumers, although accustomed to concentrate-fed beef in their marketplace, compromised palatability for meat they perceived to be leaner and more healthful.     

DIFFERENCE TASTE THRESHOLDS FOR SUCROSE IN WATER AND IN ORANGE JUICE: AN INTERLABORATORY STUDY

Difference taste thresholds, expressed as jnd values or Weberratios, were determined for sucrose in water and in orange juiceat laboratories in Sweden, U.S.A., Poland and Switzerland usinga method of constant stimuli. The following total arithmeticmean values of all 172 individual jnd values were obtained:0.266 and 0.400% sucrose at 2 and 5% sucrose in water, respectively;0.977 and 1.19% sucrose at 1.5 and 3.75% sucrose in orange juice,respectively. The frequency distributions of the individualvalues were asymetrical and showed a large variation among subjects.The results of some additional experiments at 2 and 5% sucrosein orange juice, performed only by the Polish laboratory, arereported also. Significance analyses performed according to one parametricmethod (t-test), using pooled data of groups of subjects, andone non-parametric method (Mann-Whitney's U-test), using individualthreshold values, gave the same conclusion in practically allcases. The data indicated that females had slightly lower average discriminationthresholds than males. There was a significant degree of correlationbetween subjects' discriminatory ability at different concentrationsof sucrose in each of the two media. Few significant differences between the laboratories were foundfor sucrose in water, whereas for sucrose in orange juice thefollowing rank order, from lowest to highest average jnd value,among the laboratories was obtained for both concentrationstested: Poland < U.S.A. < Sweden = Switzerland. Some speculationswere advanced as partial explanation for the differences amongthe laboratories. ^*Formerly Johansson     

FLAVOR THRESHOLDS FOR VANILLIN AND PREDICTIONS OF HIGHER OR LOWER THRESHOLDS

Thesholds for vanillin dissolved in water were determined first by 32 panelists, then by 100 additional panelists. Extreme-value analysis was applied to the results from the first 32 determinations to estimate the likelihood of thresholds later encountered being even lower than those already detected. No threshold among the 100 additional determinations was below the 5% confidence limit for the regression curve based on the 32 determinations originally made. There was evidence that some panelists were ageusic to vanillin in aqueous solution. Although some investigators have suggested that the frequency distribution for threshold values of vanillin is bimodal, application of the Kolmogorov-smirnov test to the distribution of the 132 values, as natural logarithms, gave little cause to reject the hypothesis that the distribution was unimodal.     

EVALUATION OF BITTERNESS AND ASTRINGENCY OF (+)-CATECHIN AND (-)-EPICATECHIN IN RED WINE AND IN MODEL SOLUTION

Two stereoisomeric phenolic compounds, (+)-catechin and (-)-epicatechin, were rated for perceived intensity of oral astringency and bitterness by trained judges using the scalar method. Mouth drying and mouth roughening were also assessed, since they are often associated with astringency. Amounts of 375, 750 and 1500 mg/L of each compound were tasted in red wine, and in a model system, similar in composition to a dry table wine. Preliminary tests showed that these concentrations were above the threshold level but within the range found in wine. A control sample (model solution or wine without the addition of the above phenolic compounds) was also evaluated. The results showed that the two compounds were both bitter and astringent. The high (-)-epicatechin concentration was significantly more bitter and astringent than the equal concentration of (+)-catechin in the model solution. Mouth drying and roughening ratings showed a similar increasing pattern with the ratings of astringency particularly at the higher concentrations. However, these attributes were rated differently from astringency suggesting that although they contribute to astringency, they are not subsumed by it.     

EVALUATION OF WINE QUALITY USING A SMALL-PANEL HEDONIC SCALING METHOD

A hedonic scoring method for evaluating wines with a small panel was examined for reliability, effects of training level and agreement with a traditional 20-point scoring technique. The method was found to differentiate among qualities of 14 domestic Sauvignon Blanc wines with good reliability. Four panels were tested, three with a high degree of experience in wine judging and a fourth consisting of fine wine consumers with no special training. The three experienced panels agreed well about the wines' quality scores. Mean panel scores were less highly correlated (although still positive) with the untrained panel, which showed higher variability and lower reliability. Mean scores from the hedonic method were correlated at r =+0.94 with mean scores from a 20-point quality judging procedure. The small panel hedonic method is suitable for generating quality scores for consumer guidance in large scale wine surveys, as are commonly found in popular wine periodicals.     

SENSORY EVALUATION OF CHEDDAR CHEESE MADE WITH SODIUM CHLORIDE OR MIXTURES OF SODIUM AND POTASSIUM CHLORIDE

Cheddar cheese (three trials) was made from split lots of curd, salted with NaCl or mixtures of NaCl/KCl and ripened at 3 ± 1C. Preferences for cheese, as determined by consumer panels, were significantly (P < 0.05) affected by flavor and order of presentation to panelists but not (P > 0.05) by age of cheese. In the first order of presentation, cheese made with NaCl was preferred over those made with NaCl/KCl, whereas in the second order of presentation cheese made with 1.52% NaCl/KCl (2:1) was preferred. In the third order of presentation, cheese made with 1.72% NaCl (rather than 1.5%) was preferred. Overall, mean scores were higher for cheeses made with NaCl than with NaCl/KCl. However, the score of cheese made with ca. 1.5% NaCl/KCl was not significantly (P > 0.05) different from that of cheese made with ca. 1.5% NaCl. Cheese made with ca. 1.5% NaCl/KCl (2:1) was consistently preferred over cheeses containing more KCl.     

A SEMI-ASCENDING PAIRED DIFFERENCE METHOD FOR DETERMINING SENSORY THRESHOLDS OF ADDED SUBSTANCES TO BACKGROUND MEDIA

A testing procedure was developed to determine the concentration range including an absolute or difference threshold for a compound added to a background medium. Samples were arranged into three groups, each containing a labeled control and three randomly arranged samples. Random samples in each group included an unlabeled control and two samples containing adjacent concentration levels from a series of six increasing concentrations of the added substance. Groups were presented in ascending order by concentration of the added substance. Within each group, panelists rated each sample on a nine-point intensity scale of difference from the labeled control. Group specific psychological errors in judgement were reduced by subtracting the unlabeled controls from the sample scores. Analysis of variance was applied to these data yielding separate estimates of variance for sample scores within groups. Sets of t-tests from paired comparisons were used to construct a confidence statement regarding a threshold interval.     

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.