Stimulus and recognition thresholds for the basic tastes in deionized water

Peer-reviewed | Manuscript received: March 20, 2014 | Revision accepted: May 26, 2014

Are the recommendations for citric acid too high?

Introduction

The international standard ISO 3972 [1] and the corresponding national DIN standard [2] provide guidelines for examining human taste sensitivity in the context of sensory trials. For example, recommendations are given on the chemicals and reagents to be added, e. g., the type of water used for preparing solutions of taste stimuli. The water should be “neutral, tasteless, still and odourless, preferably of known hardness” [1].

For international taste research, deionized water is mostly used to prepare the solutions (see e.g. [3–6]). This ensures that comparability between different study centres is ensured and that the composition of the water is relatively stable – independent of the site of production. Nevertheless, the evaluation of the results of a large study [7] raised doubts as to whether deionized water is suited for the measurement of taste sensitivity for sour.¹ It is thought that either (a) the citric acid concentration would have to be adjusted or (b) another type of water would have to be used to dissolve the substance.

Moreover, ISO 3972 [1] (with the corrigendum of 2012 [8]), as well as the corresponding national DIN ISO 3972 [2] refer – in contrast to the previous versions [9, 10] – to lower thresholds for bitter and sour in demineralised water, without explaining what is meant by “lower” or giving detailed references to alternative concentrations for the substances.

Summary

During the recruitment of sensory panelists (e.g. when screening assessors suitability or training of assessors), the sensitivity for basic tastes is often measured with threshold tests. The present study examined the concentrations of taste stimuli used in the threshold tests in accordance with ISO and DIN [1, 2], with respect to their applicability in deionized water. The taste thresholds for sweet, sour, salty, bitter, umami and metallic were determined for 70 young European women. With eight increasing concentrations, it was found that the individual taste stimuli for sweet, salty, bitter, umami and metallic were well distributed. However, sour was recognized by all study participants within the two lowest concentrations. Clear differences in sensitivity were achieved by reducing the citric acid concentration to a fifth of the original value. Thus, if deionized water is used as solvent, the citric acid concentration must be reduced if the expected differences in perceived sourness are to be found.

Keywords: taste sensitivity, threshold, citric acid, type of water, sensory science

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