Is caffeine a flavoring agent in cola soft drinks?

Background: Concern has been expressed about the nutrition and health impac t of high rates of soft drink consumption. Caffeine is an added ingredient in approximately 70% of soft drinks consumed in the United States. The soft drink manufacturers' justification to regulatory agencies and the public f or adding caffeine to soft drinks is that caffeine is a flavoring agent. Objective: To examine the claim that caffeine plays an integral role in the flavor profile of soft drinks, by examining the effect of caffeine on the threshold for detection of flavor differences in cola beverages. Design: Double-blind crossover study starting November 1998 and ending July 1999. Setting: An academic research center. Participants: Twenty-five adult regular consumers of cola soft drinks, Base d on a screening session, all were able to detect a flavor difference betwe en cola containing sugar and diet cola. Intervention: A sensitive version of a forced-choice flavor-detection proce dure was used to evaluate the effects of a wide range of caffeine concentra tions (range, 0.05-1.6 mg/mL) on the ability to detect flavor differences b etween caffeinated and caffeine-free cola beverages. Repeated tests permitt ed determination of significant detection at each concentration in individu al subjects. Main Outcome Measures: Percentage of subjects significantly detecting a fla vor difference and mean percentage of trials correct at each caffeine conce ntration. Results: Detection of flavor differences increased as a function of caffein e concentration. At the 0.1-mg/mL concentration, which is the approximate c oncentration in the majority of cola soft drink products, 2 subjects (8%) s ignificantly detected a flavor difference and the mean percentage correct ( 53%) was at chance levels. Conclusions: The finding that only 8% of a group of regular cola soft drink consumers could detect the effect of the caffeine concentration found in m ost cola soft drinks is at variance with the claim made by soft drink manuf acturers that caffeine is added to soft drinks because it plays an integral role in the flavor profile. It is valuable for the general public, the med ical community, and regulatory agencies to recognize that the high rates of consumption of caffeinated soft drinks more likely reflect the mood-alteri ng and physical dependence-producing effects of caffeine as a central nervo us system-active drug than its subtle effects as a flavoring agent.