Challenges in using Electronic tongue to study rasa of plants: II. Impact of solvent and concentration on sensor response and taste ranking

BACKGROUND: Although Electronic tongue is used in pharmaceutical, food and beverage industries for objective evaluation of taste, its use in medicinal plants from an ayurvedic perspective is novel. Control experiments are therefore necessary to standardise and optimise parameters. OBJECTIVE: The aim is to optimise the use of solvent and standardise sample concentration for study of plants from an ayurvedic standpoint of rasa. The major objectives are two-fold: (i) evaluate sensor response to different types of solvent water (ii) explore use of E-tongue in taste ranking of medicinal plants used in ayurveda. MATERIALS AND METHODS: Single, double and triple distilled, reverse osmosis and milliQ waters were evaluated separately and as a medium for preparing plant extracts. For taste ranking, standard addition method using d-glucose as sweet taste standard was used for different brands of mango juices (case in point study) and eight medicinal plants from sweet category. The effect of sample concentration and taste standard on taste ranking were evaluated. RESULTS: MQ and TD water demonstrated similar organoleptic properties whereas plant extracts prepared in DD and MQ water showed maximum taste-based differentiation. The mango juices were taste discriminated by E-tongue and ranked based on their sweetness scores. The relative ranking of plant samples showed concentration dependence and also varied with the concentration range of taste standard. CONCLUSION: Milli-Q and double distilled water can be used for E-tongue studies of medicinal plants. While the results open up the possibility of taste ranking of medicinal plants, they also demonstrate the importance of standardising and optimising the concentration of samples and taste standards in the context of ayurvedic rasa based studies.