Utilizing the R-index measure for threshold testing in model caffeine solutions

The objective of this study was to validate the use of R-index measure by the rating method for bitterness threshold testing. Untrained panelists (32 people) used the R-index rating method to determine difference thresholds for caffeine. Caffeine solutions (7) in spring water represented the signal. Panelists received five replicates each of noise and signal for R-index rating test and one replicate of the ASTM method of ascending limits. In the second part of the study, 15 randomly selected panelists completed another five replicates of R-index rating test and four replicates of ASTM test. The R-index group threshold for the initial panel was 0.0260 g caffeine/100 ml and 0.0148 g/100 mL for the second panel. Group thresholds, using the ASTM method, were 0.0291 g/100 ml for the first panel and 0.0309 g/100 ml for the second panel. These values are within the 0.0136-0.0350 g/100 ml literature threshold range of caffeine.