Elsevier

Fitoterapia

Volume 86, April 2013, Pages 137-143
Fitoterapia

Sensory evaluation of the taste of berberine hydrochloride using an Electronic Tongue

https://doi.org/10.1016/j.fitote.2013.02.010Get rights and content

Abstract

Background

The “Electronic Tongue” is an instrument that can be trained to screen the taste attributes of formulations within a rapid timeframe when used in conjunction with sensory panel taste assessment data.

Purpose

The purpose of this research was to demonstrate that a sensory instrument for taste (e-Tongue) could be used to evaluate the bitterness of berberine hydrochloride from Chinese medicinal herbs.

Methods

Several flavorful native compounds were tested by the e-Tongue. Data from a human sensory panel was collected to train the e-Tongue. The e-Tongue was then used to establish the correlation between data from the sensory panel, and to predict the bitterness scores of berberine hydrochloride.

Results

The e-Tongue showed different response patterns for different tastes or strengths of flavor compounds. No significant differences were found between the results of the e-Tongue and the sensory taste panel.

Conclusions

The e-Tongue could be used to evaluate the effect of bitterness of berberine hydrochloride. Therefore, e-Tongues showed potential to replace sensory panel evaluations in future experiments regarding Chinese traditional medicine.

Introduction

Oral pharmaceutical products residing in the mouth long enough to be tasted should be palatable. Palatable attributes include appearance, taste, smell, and texture. Palatability could significantly affect compliance and therefore dictate whether a successful or unsuccessful therapeutic outcome is attained. Palatability of the drug product should be given careful consideration to achieve optimal efficacy, as the drug is useless if the patient does not or cannot take the medication. The current methods that can assess the bitterness of agents mainly comprise sensory panel evaluations.

At present, research into bitter receptors on human taste bud cells is a hotspot in palate research. In humans, bitter taste is mediated by G protein-coupled receptors that belong to the TAS2R gene family, which contains 25 TAS2R genes [1], [2]. Researchers had investigated the molecular receptive ranges of bitter taste receptors using 104 natural or synthetic bitter chemicals to challenge all of the 25 human TAS2R genes in transfected cells [3]. The results indicated that the detection of the numerous bitter chemicals is related to the molecular receptor ranges of hTAS2Rs, which explains how the vast array of bitter compounds can be detected by such a limited number of sensors. However, these experiments were carried out on rats or in vitro, and many phenomena remain poorly understood.

The “Electronic Tongue” (e-Tongue) has recently become available [4]. This is an instrument that can be trained to screen the taste attributes of formulations within a rapid timeframe when used in conjunction with human taste assessment data. Several pharmaceutical laboratories are using this instrument to assess the bitterness of active pharmaceutical ingredients (APIs) and the masking efficiency. In addition, it is also used in the development of placebos, in taste matching of formulations, and in unknown-to-reference comparisons [5], [6], [7], [8], [9], [10], [11].

The first multi-sensor system for liquid analysis based on a non-specific sensor approach was a taste sensor termed the e-Tongue introduced in 1990 by Toko et al. [12]. It was followed by several other sensors based on different principles, including the Voltammetric Electronic Tongue, Biofilm Electronic Tongue and PVC Electronic Tongue. However, these studies [13], [14], [15], [16] were conducted with pilot e-Tongue models with short life sensors, thereby significantly limiting their application. Recently, a taste analyzing system manufactured by Alpha MOS has become commercially available. The taste sensors consist of silicon transistors with an organic coating that governs sensitivity and selectivity of each individual sensor. The sensors are estimated to last up to one year.

Assessment of the taste and flavor of oral drug preparations is of major interest to the pharmaceutical industry, particularly for research-based companies. Typical tasks include evaluation of taste changes due to aging, masking of unpleasant (usually bitter) taste of active substances or the selection of the least bitter-tasting molecules from a number of new chemical entities.

Drugs used in traditional Chinese medicine (TCM) have varied tastes (predominantly sweet, bitter, pungent or astringent), some of which are particularly complex as they have several active constituents [17]. The compound berberine hydrochloride is a quaternary ammonium salt from the isoquinoline alkaloid group. It is found in plants including berberis, goldenseal (Hydrastis canadensis), and Coptis chinensis, and is usually present in the roots, rhizomes, stems and bark. It has a typical bitter taste. This study used the bitter score both from an e-Tongue and from a human sensory panel to establish a possible correlation between the two techniques. The bitterness scores of berberine hydrochloride were detected by an e-Tongue and the prediction was performed by the sensory panel data.

The objectives of this study were as follows:

  • (i)

    To use the flavored natural products to assess the cross-sensitivity of the different flavor compounds.

  • (ii)

    To investigate the potential use of an e-Tongue in ranking the relative bitterness of compounds, in order to screen for better taste-masking agents and their appropriate use level.

  • (iii)

    To prove that an e-Tongue can be used to evaluate the effect of the bitterness of berberine hydrochloride.

Section snippets

Materials

Sodium l-glutamate (MSG), NaCl, quinine and caffeine were obtained from Alpha MOS Inc. Steviol glycosides were supplied by Shanghai Kaisai Chemical Engineering Co., Ltd., China. Citric acid, Super Sweet (a compound of different sweeteners), acesulfame-K, and sucralose were obtained from Zhangzhou Shengyuan Chemical Products Co. Ltd., China. Matrine, amygdalin, and naringin were obtained from Nanjing Langze Agricultural Development Co. Ltd., China. Berberine hydrochloride was obtained from Lion

Cross-selectivity of taste sensors to different taste substances

Seven sensors were made from silicon transistors with an organic coating that governs selectivity and sensitivity of each individual sensor. The coatings were developed to ensure high repeatability, sensitivity and selectivity. Details on sensor materials have not been disclosed by the manufacturer due to a current patent application.

With a set of cross-selective taste sensors, each sensor could concurrently contribute to the detection of most substances in a sample, although the sensitivity to

Conclusions

The e-Tongue was capable of discriminating between substances with a different taste, and the sensors appeared to be cross-selective for five basic tastes: sourness, sweetness, bitterness, saltiness, and umami. A strong linear relationship for berberine hydrochloride was observed in the concentration range of 0.93 mg/l–18.63 mg/l. An e-Tongue can be successfully used to screen for better taste-masking agents and for optimal concentrations. This would have the benefit of providing pharmaceutical

Acknowledgment

This work was supported by grants from Shanghai Leading Academic Discipline Project (Grant Number: J50302), the Research Fund for the Doctoral Program of Higher Education of China (Grant Number: 20103107110011), and the National Sci-Tech Major Special Item (Grant Number: 2009ZX09502-009).

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