ABSTRACT
A taste sensor system was applied to the evaluation of tea tastes. In order to enhance the accuracy of the measurements, a standard solution was prepared from pure chemicals, and the values indicating the taste intensities were calculated using two standard substance solutions with different concentrations. (–)-Epigallocatechin-3-O-gallate (EGCg) and monosodium glutamate (MSG) were adopted as standard substances for the measurements of the astringent and umami taste intensities, respectively. The astringent taste intensities of Japanese green teas were classified into 8 grades. While their intensities were correlated with the concentrations of the major tea catechins as a whole, they also appeared to be influenced by other factors. The umami taste
intensity of Japanese green tea was classified into 6 grades. In this case, before the measurement, the catechins in the tea infusion were removed with poly(vinylpolypyrrolidone) (PVPP), because the umami sensor unexpectedly responded to the catechins. Furthermore, the astringent taste intensity of Indian and Sri Lankan black tea was classified into 10 grades by applying the evaluation method developed for green tea. Sensory tests proved that these sensor results correlated with the human gustatory sense. 3.1 IntroductionTea is an agricultural product made from a bud and young leaves of tea plants [Camellia sinensis (L.), O. Kuntze], and the infusion is a globally consumed beverage. The taste of tea is one of its most important quality factors, in addition to the flavor and color of the infusion and has been traditionally evaluated by a sensory test. For example, in the case of Sencha, a representative Japanese green tea, a good evaluation is given for a sample with moderate harmony among sweetness, bitterness, umami taste, and astringency, a mild taste, and a fresh feeling. Astringency, bitterness, and unpleasant tastes such as harsh taste, acid taste, burned taste, and tastes associated with fermentation are regarded as bad properties.1However, there are some problems with this sensory test. First, the evaluation results include subjective factors. In order to gain more objectivity in sensory tests, there is a method based on the primary taste intensities, which are evaluated by panelists trained with reference samples.2 However, such an evaluating system is not used in the tea examination. Moreover, many evaluation items are required, and the definitions of the evaluations are ambiguous. For example, the criteria for a moderate harmony, a mild taste, or a fresh feeling are unclear. Therefore, there is large room for the subjective view of the panelists. Second, the terms representing tea qualities are complicated. It is not easy for consumers to imagine the actual taste from this information. Third, there is a limit to the number of tea samples that can be evaluated in one examination, and it is impossible to compare evaluation results between samples separated in time (for example, results between this year and last year).
