Repeated-measures ANOVAs performed on the log intensity ratings for the 4 taste stimuli and PROP () indicated that there were main effects of stimulus (F4,328 = 18.54, P < 0.00001) and replicate (F1,82 = 10.94, P < 0.002). Tukey's HSD tests (P < 0.05) further confirmed that the effect of stimulus was derived from significantly lower average bitterness ratings of PROP, whereas the perceived intensities of the 4 prototypical taste stimuli did not differ significantly from one another. In addition, although there was a tendency for the replicate ratings to be higher than the initial ratings for all but NaCl, the first and second intensity ratings were not significantly different for any of the 5 stimuli. Pearson product-moment correlation coefficients calculated for the 2 ratings of each stimulus () also showed that there was a degree of consistency across replicates (e.g., r = 0.71 for sucrose and 0.72 for PROP). However, correlations between different taste stimuli were generally not significant after Bonferroni correction. The sole exception was a significant correlation between bitterness ratings of QHCl and PROP. On the other hand, when taste intensity ratings were averaged across replicates, correlations among all 4 prototypical taste stimuli, excluding PROP, were significant (). Because the distributions between the bitterness of PROP and other tastes are possibly different (i.e., bimodal vs. normal distribution), we also calculated Spearman's rank-order correlations, which gave results that agreed with those from the Pearson product-moment correlation.
Figure 1 Log means of perceived intensity ± standard error of the relevant taste (sweetness for sucrose, saltiness for NaCl, sourness for citric acid, bitterness for QHCl, and bitterness for PROP). The different letters indicate significant differences (more ...)
Correlation coefficients (r) between replicate taste intensity ratings
Correlation coefficients (r) between stimuli after averaging across replicates
shows the mean log perceived intensity ratings for the primary qualities of the prototypical taste and PROP stimuli grouped by PROP taster status. Analyses revealed no significant group differences between PT and PNT for the sweetness of sucrose, saltiness of NaCl, and sourness of citric acid, although PT's rated the bitterness of QHCl significantly higher than did PNT's (, the left panel). When the PT's were subcategorized as medium vs. supertasters, the taste intensity ratings between groups differed significantly: PST's rated the perceived intensities of all 4 prototypical taste stimuli and PROP significantly higher than did PMT's.
Figure 2 Log means of perceived intensity ± standard error for sweetness of sucrose, saltiness of NaCl, sourness of citric acid, bitterness of QHCl, and bitterness of PROP grouped by PROP taster status. The left panel shows the comparison between the PROP (more ...)
shows the mean log intensity ratings for overall flavor (left graph) and creaminess (right graph) of the 3 milk products. Two separate repeated-measures ANOVAs revealed a significant main effect of stimulus for both the perceived intensity of flavor (P < 0.0001) and creaminess (P < 0.0001). The perceived flavor and creaminess intensities increased with fat content from 0% (fat-free milk) to 10.5% (half-and-half). As expected, the subjects rated overall flavor to be significantly higher (P < 0.0001) in the condition without the nose clip. Although creaminess ratings also tended to be higher without the nose clip, Tukey's HSD tests (P < 0.05) showed that the main effect of retronasal odor on creaminess ratings was significant only for whole milk.
Figure 3 Log mean intensity ratings ± standard error for overall flavor and creaminess intensity ratings for the 3 milk stimuli varying in fat content for the nose-open and nose-closed conditions. Error bars represent standard errors. The different alphabets (more ...)
There was no significant relationship between ratings of creaminess and taste intensity for any of the taste stimuli, including PROP (). Indeed, for the averaged data, only a single significant correlation was obtained (saltiness of NaCl and creaminess of half-and-half); most other correlation coefficients were less than 0.20. Similarly, correlations between ratings of flavor intensities of the milk products and taste intensity were low (results not shown). After Bonferroni correction, the only significant correlations involved sucrose and NaCl: NaCl saltiness was correlated with the flavor intensity of half-and-half without the nose clip (r = 0.34), and sucrose sweetness was correlated with the flavor of whole milk in both the nose open and nose closed conditions (r = 0.42 and 0.32, respectively). Ratings of PROP bitterness were not significantly correlated with flavor ratings for any of the milk products in either condition (all r < 0.22).
Correlation coefficients (r) between taste intensities and creaminess ratings in nose-closed condition