Assessment of the triangle test methodology for determining umami discrimination status

Abstract
The prototypical stimuli for umami taste is monosodium glutamate (MSG), which is the sodium salt form of glutamic acid. A proportion of the population has a reduced or complete inability to taste l-glutamate independent to the sodium ion. To determine individuals’ umami discrimination status, many studies use a series of triangle tests containing isomolar (29 mM) sodium chloride (NaCl) and MSG, requiring participants to correctly identify the odd sample. Across studies, inconsistent categorization criteria have been applied. The aim of this study was to determine the optimal classification criterion based on the number of tests assessed to ascertain an individual’s ability to discriminate between MSG and NaCl. Thirty-eight participants attended 3 taste assessment sessions, each involving 24 triangle tests (2 blocks of 12 tests) containing 29 mM NaCl and 29 mM MSG, detection and recognition threshold were measured for MSG, monopotassium glutamate (MPG), and sweet (sucrose) tastes. There was no learning, or fatigue trend over n = 24 (P = 0.228), and n = 12 (P = 0.940) triangle tests across each testing session. Twenty-four triangle tests produced the most consistent categorization of tasters across sessions (68.4%). The test–retest correlation across each testing session was highest for n = 24 triangle tests (ICC = 0.50), in comparison to 12 (ICC = 0.37). Overall, conducting n = 24 compared with n = 12 triangle tests provided the optimal classification to determine an individual’s ability to discriminate l-glutamate from NaCl and thus their umami discrimination status, based on the number of tests assessed in this study.