Bitterness suppression of BCAA solutions by L-ornithine

The purpose of the present study was to evaluate the bitterness-suppressing effect of L-ornithine (L-Orn) on single or mixed solutions of branched-chain amino acids (BCAAs) using human gustatory sensation tests and an artificial taste sensor. The BCAAs tested (L-isoleucine (L-Ile), L-leucine (L-Leu), and L-valine (L-Val)) are the main components of various enteral nutrients or supplements. The bitterness-suppression effect of L-Orn was also compared with the effect of L-Arg. L-Orn was effective in suppressing the bitterness of single or mixed solutions of BCAAs in human gustatory sensation tests, the effect being similar to or greater than that of L-Arg. The artificial taste sensor was able to predict the bitterness-suppressing effects of L-Orn and L-Arg. The response electric potential patterns of L-Val, L-Leu and L-Ile solutions to which 100 mM L-Arg had been added were quite similar to the sensor response patterns of the 100 mM L-Arg solutions alone. The relative response electric potential patterns of L-Val, L-Leu or L-Ile solutions containing 100 mM L-Orn in channels 5-8 (positively charged) are similar to that of single solution of 100 mM L-Orn.     

A new method for evaluating the bitterness of medicines by semi-continuous measurement of adsorption using a taste sensor

We describe a new method for the evaluation of the bitterness of medicines by semi-continuous measurement of adsorption using a multichannel taste sensor or 'electric tongue'. The bitterness of 10 basic medicines was evaluated by both the taste sensor and in human gustatory sensation tests with 11 volunteers. The sensor part of the taste sensor consists of eight electrodes made of lipid/polymer membranes. Three variables were obtained from the taste sensor data: sensor output (S), the change of membrane potential caused by adsorption, corresponding to aftertaste (C), and the ratio C/S. These variables were used to predict an estimated bitterness score in multiple regression analysis. Semi-continuous measurement of C (every 30 s up to 150 s) was adopted as an additional explanatory variable, and the attenuation rate of C was defined as C'. These data were also subjected to multiple regression analysis. The correlation coefficient (r) estimated for the bitterness score predicted by the taste sensor, using C' for channel 2 and C/S for channel 4, and the score obtained by human gustatory sensation, was 0.824. This value was greater than that obtained using C/S for both channels 2 and 4 (0.734). The method described in the present study seems to offer good predictability for the evaluation of bitterness.     

Bitterness evaluation of medicines for pediatric use by a taste sensor

The purpose of this study was to evaluate the bitterness of 18 different antibiotic and antiviral drug formulations, widely used to treat infectious diseases in children and infants, in human gustatory sensation tests and using an artificial taste sensor. Seven of the formulations were found to have a bitterness intensity exceeding 1.0 in gustatory sensation tests (evaluated against quinine as a standard) and were therefore assumed to have an unpleasant taste to children. The bitterness intensity scores of the medicines were examined using suspensions in water or an acidic sports drink. In the case of three macrolide antibiotic formulations containing erythromycin (ERYTHROCIN dry syrup), clarithromycin (CLARITH dry syrup for pediatric), and azithromycin (ZITHROMAC fine granules for pediatric use), the bitterness intensities of suspensions in acidic sports drinks were dramatically enhanced compared with the corresponding scores of suspensions in water. This enhancement could be predicted using the taste sensor. On the other hand, a reduction of bitterness intensity was observed for an acidic sports drink suspension of an amantadine product (SYMMETREL fine granules) compared with an aqueous suspension. This reduction in bitterness could also be predicted using the taste sensor output value. Thus, the taste sensor could predict whether or not suspension in an acidic sports drink would enhance or reduce the bitterness intensity of pediatric drug formulations, compared with suspensions in water.     

The quantitative prediction of bitterness-suppressing effect of sweeteners on the bitterness of famotidine by sweetness-responsive sensor

The purpose of the present study was the quantitative prediction of the bitterness-suppressing effect of sweeteners (sucrose or sugar alcohols) on the bitterness of famotidine (or quinine sulfate as control) solutions using an artificial taste sensor. Firstly, we examined the response characteristics of the sensor response to sweetness. The sensor membrane is charged negatively in the presence of sweeteners, which tend to receive protons from one of the components of the sensor membrane. The magnitude of the sensor response was shown to increase in direct proportion to the concentration of the sweetener. Secondly, we used direct or indirect methods to evaluate and predict the bitterness-suppressing effect of sweeteners on 1 mg/ml famotidine and 81.4 microM quinine sulfate solutions. In direct method, a regression between the sensor output of the sweetness-responsive sensor and the bitterness intensity obtained in human gustatory tests of famotidine solutions containing sweeteners at various concentrations, was performed. As a result, we were able to predict directly the bitterness intensity of the mixed solution. Finally, we also evaluated the bitterness intensity of the dissolution media of commercially available, orally disintegrating tablets containing famotidine by the combined usage of bitterness- and sweetness-responsive sensor. We found that the sugar alcohols in the tablet seem to be effective in the bitterness-suppression of famotidine from these tablets, especially in the initial phase (within 30 s) of the disintegration process.     

Quantitative taste evaluation of total enteral nutrients

The purpose of this study was to evaluate quantitatively the taste of the various total enteral nutrients marketed in Japan using human gustatory sensation tests and an artificial taste sensor. In the human gustatory sensation test, four basic taste intensities (sweetness, saltiness, sourness, and bitterness), as well as 15 kinds of palatability scales, were evaluated according to the semantic differential (SD) method. Among 15 palatability items, the item; difficult to drink/easy to drink, was adopted as an overall palatability since it shows the highest factor loading by factor analysis. The overall palatability was found to be highly positively correlated with sweetness and sourness, but negatively correlated with bitterness and saltiness. Addition of a flavour to the amino acid-based enteral nutrient AminolebanEN significantly improved its palatability. This effect is presumably due to sour components of the flavour, such as citric acid, which reduce the bitterness intensity of branched-chain amino acids in the product. The sweetness and sourness intensities predicted by the taste sensor showed a high correlation with the results obtained in the human gustatory sensation tests. The taste sensor was able to predict the overall palatability of the total enteral nutrients with high accuracy. The products could be classified into three groups (peptide-based, amino-acid-based, and protein-based) by principal component analysis using sensor output of 8 channels. The products could be also classified into four groups; peptide-based, amino-acid-based, and protein-based and flavor addition group by principal component analysis using sensor output of channels 1, 3, 4 and 7, which are specific to basic tastes. The taste sensor could therefore be useful in predicting the taste or palatability of total enteral nutrients, and could contribute to attempts to improve compliance for such products and for enteral nutrients.     

The combination effect of L-arginine and NaCl on bitterness suppression of amino acid solutions

The purpose of the present study was to quantify the degree of suppression of the bitterness of two amino acids (L-isoleucine (L-Ile), and L-phenylalanine (L-Phe)) which could be achieved by the addition of various test chemicals, and to examine the mechanism of this bitterness suppression. The test chemicals used were two sweeteners (sucrose, aspartame), NaCl, various acidic (L-aspartic acid, L-glutamic acid), or basic (L-histidine, L-lysine and L-arginine) amino acids, tannic acid and phosphatidic acid. The combination of L-arginine (L-Arg) and NaCl together was the most effective in reducing the bitterness of 100 mM L-Ile and L-Phe solutions in human gustatory sensation tests. Even in bitterness of 0.1 mM quinine solution, L-Arg was also successful in reducing the bitterness. This bitterness-suppression effect was specific to L-Arg and not to the other basic amino acids. No comparable taste-masking effect was observed for the acidic amino acids. The artificial taste sensor failed to predict completely the bitterness-suppressing effect of L-Arg. It seems likely that the bitterness-suppressing effect of L-Arg is mediated not only by binding at the receptor site, but also elsewhere in the process of bitterness perception, such as a direct effect on the sodium channel. It is conjectured that the guanidinium group of L-Arg may interact with sodium channels in taste bud membranes.     

Evaluation of bitterness suppression of macrolide dry syrups by jellies

The purpose of this study was to evaluate the bitterness-suppressing effect of three jellies, all commercially available on the Japanese market as swallowing aids, on two dry syrups containing the macrolides clarithromycin (CAM) or azithromycin (AZM). The bitterness intensities of mixtures of the dry syrups and acidic jellies were significantly greater than those of water suspensions of the dry syrups in human gustatory sensation tests. On the other hand, the mixture with a chocolate jelly, which has a neutral pH, was less bitter than water suspensions of the dry syrups. The bitterness intensities predicted by the taste sensor output values correlated well with the observed bitterness intensities in human gustatory sensation tests. When the concentrations of CAM and AZM in solutions extracted from physical mixtures of dry syrup and jelly were determined by HPLC, concentrations in the solutions extracted from mixtures with acidic jellies were higher than those from mixtures with a neutral jelly (almost 90 times higher for CAM, and almost 7-10 times higher for AZM). Thus, bitterness suppression is correlated with the pH of the jelly. Finally, a drug dissolution test for dry syrup with and without jelly was performed using the paddle method. There was no significance difference in dissolution profile. It was concluded the appropriate choice of jelly with the right pH is essential for taste masking. Suitable jellies might be used to improve patient compliance, especially in children. The taste sensor may be used to predict the bitterness-suppressing effect of the jelly.     

The bitterness intensity of clarithromycin evaluated by a taste sensor

The purpose of this study was to evaluate the ability of a quantitative prediction method using a taste sensor to determine the bitterness of clarithromycin powder suspensions of various concentrations and of a commercial clarithromycin dry syrup product (Clarith dry syrup, Taisho Pharmaceutical Co., Ltd., Tokyo) containing aminoalkyl methacrylate polymer as a taste-masker. The bitterness of the clarithromycin dry syrup product dissolved in various beverages was also evaluated in gustatory sensation tests and using the taste sensor. In the sensor measurements, three variables were used to predict bitterness in single and multiple regression analysis: relative sensor output (R), the change of membrane potential caused by adsorption (CPA), and CPA/R ratio. The CPA values for channel 3 of the sensor predicted well the bitterness of clarithromycin powder suspensions and their filtered solutions. For Clarith dry syrup, the sensor output was small, suggesting that aminoalkyl methacrylate polymer was successful in almost complete masking of the bitter taste of the dry syrup product. When the bitterness intensities of mixtures of 1 g of Clarith dry syrup with 25 ml of water, coffee, tea, green tea, cocoa, milk, and a sports drink were examined, a good correlation was obtained between the results from human taste tests and the predicted values calculated on the basis of multiple regression analysis using CPA data from channel 4, and the CPA/R ratio from channel 3 of the taste sensor (r(2)=0.963, p<0.005). Co-administration of 1 g of Clarith dry syrup with an acidic sports drink was found to be the most bitter using either method.     

The effect of various substances on the suppression of the bitterness of quinine-human gustatory sensation,binding, and taste sensor studies

The purpose of this study was to quantify the degree of suppression of the perceived bitterness of quinine by various substances and to examine the mechanism of bitterness suppression. The following compounds were tested for their ability to suppress bitterness: sucrose, a natural sweetener; aspartame, a noncaloric sweetener; sodium chloride (NaCl) as the electrolyte; phosphatidic acid, a commercial bitterness suppression agent; and tannic acid, a component of green tea. These substances were examined in a gustatory sensation test in human volunteers, a binding study, and using an artificial taste sensor. Sucrose, aspartame, and NaCl were effective in suppressing bitterness, although at comparatively high concentrations. An almost 80% inhibition of bitterness (calculated as concentration %) of a 0.1 mM quinine hydrochloride solution required 800 mM of sucrose, 8 mM of aspartame, and 300 mM NaCl. Similar levels of bitterness inhibition by phosphatidic acid and tannic acid (81.7, 61.0%, respectively) were obtained at much lower concentrations (1.0 (w/v)% for phosphatidic acid and 0.05 (w/v)% for tannic acid). The mechanism of the bitterness-depressing effect of phosphatidic acid and tannic acid was investigated in terms of adsorption and masking at the receptor site. With phosphatidic acid, 36.1% of the bitterness-depressing effect was found to be due to adsorption, while 45.6% was due to suppression at the receptor site. In the case of 0.05 (w/v)% tannic acid, the total bitterness-masking effect was 61.0%. The contribution of the adsorption effect was about 27.5% while the residual masking effect at the receptor site was almost 33%. Further addition of tannic acid (0.15 (w/v)%), however, increased the bitterness score of quinine, which probably represents an effect of the astringency of tannic acid itself. Finally, an artificial taste sensor was used to evaluate or predict the bitterness-depressing effect. The sensor output profile was shown to reflect the depressant effect at the receptor site rather well. Therefore, the taste sensor is potentially useful for predicting the effectiveness of bitterness-depressant substances.     

The suppression of enhanced bitterness intensity of macrolide dry syrup mixed with an acidic powder

The aim of the present study was to identify a medicine which strongly enhanced the bitterness of clarithromycin dry syrup (CAMD) when administered concomitantly and to develop a method to suppress this enhanced bitterness. The bitterness enhancement was evaluated not only by gustatory sensation tests but also using pH and taste sensor measurements of the mixed sample. A remarkable bitterness enhancement was found when CAMD was mixed with the acidic powder L-carbocysteine. The acidic pH (pH 3.40) of the suspension made from these two preparations, seemed to be due to enhanced release of clarithromycin caused by the dissolution of the alkaline polymer film-coating. Several methods for preventing this bitterness enhancement were investigated. Neither increasing the volume of water taken with the mixture, nor changing the ratio of CAMD:L-carbocysteine in the mixture, were effective in reducing the bitterness intensity of the CAMD/L-carbocysteine mixture. The best way to achieve taste masking was to first administer CAMD mixed with chocolate jelly, which has a neutral pH, followed by the L-carbocysteine suspension. Similar results were obtained for the bitterness suppression of azithromycin fine granules with L-carbocysteine. The chocolate jelly will be useful for taste masking of bitter macrolide drug formulations, when they need to be administered together with acidic drug formulations.     

Study of the physicochemical properties of tulobuterol dry syrups using taste and smell sensors

The purpose of the present study was to evaluate the taste and smell of Tulobuterol Dry Syrup (TB-DS) in its original form (formulation A) and generic form (formulations B and C) by means of gustatory sensation tests and taste and smell sensors. In addition, the physicochemical properties of the syrups in a solid state were compared. Evaluation of sweetness with a powdered sample revealed significant differences between formulation A and formulation B and between formulation B and formulation C. In contrast, the results of principal component analysis (PCA) with a taste sensor revealed differences in principal component 1 (PC 1) among formulations A, B, and C. Smell sensor measurement of powdered samples revealed differences in products in terms of only PC 1, but these results were not related to the results of gustatory sensation testing with a smell sensor. Measurement of particle size distribution and scanning electron microscopy revealed differences in the particle diameter and particle surface shape for each product. Formulation B had the strongest absorption in the near-infrared spectrum, followed by formulation A and then formulation C. Accordingly, differences in preparations were presumably caused by variations in manufacturing specifications, such as types of additives and their content and coating methods used. In other words, the characteristics of each product were revealed by evaluation of their physical properties, sensing of taste and smell, and human gustatory sensation tests.     

Suppression of the bitterness of enteral nutrients using increased particle sizes of branched-chain amino acids (BCAAs) and various flavours: a taste sensor study

An improved formulation of the enteral nutrient Aminoleban EN (Otsuka Pharmaceutical Co., Ltd., Tokyo, Japan), has been commercially available since Spring 2004. Like the previous formulation, the improved product contains branched-chain amino acids (BCAAs) L-isoleucine (L-Ile), L-leucine (L-Leu), and L-valine (L-Val), but the average particle size of these amino acids has been increased to 180 to 250 microm in the improved formulation, compared with 40 to 90 microm in the old product. The improved formulation has a significantly lower bitterness intensity score than the older formulation, as evaluated both in human gustatory tests and using the artificial taste sensor. We propose that this improved taste masking is due to the larger particle size of the BCAA crystals, due to which their release rates are reduced. The addition of improved flavours has also helped to reduce the bitterness of the improved Aminoleban EN formulation significantly. Analysis of the taste sensor data suggests that the sourness and sweetness of the added flavours were critical in diminishing the bitterness of Aminoleban EN.     

Taste masking of propiverine hydrochloride by conversion to its free base

The aim of the present study was to mask the bitterness of propiverine hydrochloride (P-4) by converting it to propiverine free base. Fine granules comprising the free base, which was converted from P-4 by desalination, were prepared. By using Fourier transform infrared spectroscopy, thermogravimetry-differential thermal analysis, and powder X-ray diffraction spectra, we confirmed that P-4 had been converted into propiverine free base by desalination during the manufacturing process. Furthermore, the conversion into free base appeared to result in decreased solubility, and both the taste testing sensor and tasting volunteers determined that it masked the bitterness of P-4. On using the gustatory sensation test, the bitterness of the P-4 fine granules was confirmed to be weakened. The dissolution rate and bioavailability of fine granules of the free base were compared with tablets of P-4. The dissolution rate and bioavailability of the fine granules and tablets were almost the same. We successfully masked the taste of P-4 by converting it into free base using a manufacturing process that was suitable for commercial manufacturing.     

Inhibitory effect of aroma on the bitterness of branched-chain amino acid solutions

Nutritional products for patients with liver failure available on the Japanese market contain many branched-chain amino acids (BCAAs) such as L-leucine, L-isoleucine, and L-valine, which not only have a bitter taste but also strong, unpleasant odours, leading to low palatability. The palatability of these nutritional products can be significantly improved by the addition of flavoured powders containing various kinds of tastants (sucrose, citric acid, etc.) and odourants (fruit, coffee aromas, etc.). The specific effects of the aroma of flavoured powders have not yet been clearly evaluated. In the present article, the inhibitory effect of aroma on the bitterness of BCAA solutions was examined. The bitterness intensity of a BCAA solution at the same concentration as Aminoleban EN was defined as 3.5 (measured by a previously described gustatory sensation method). The bitterness threshold of a BCAA standard solution without added aroma was estimated to be 1.87, while those of BCAA solutions containing green-tea, coffee, apple, vanilla, or strawberry aromas were 2.02, 1.98, 2.35, 2.40 and 2.87, respectively, when evaluated by the probit method. This shows that the addition of an aroma can elevate the bitterness threshold in human volunteers. The green-tea and coffee aromas predominantly evoked bitterness, while the vanilla aroma predominantly evoked sweetness. Apple and strawberry aromas evoked both sweetness and sourness, with the apple aroma having stronger sourness and the strawberry aroma stronger sweetness. Thus, a 'sweet' aroma suppresses the bitterness of BCAA, with coexisting sourness also participating in the bitterness inhibition.     

Factors affecting the bitterness intensities of ten commercial formulations of ambroxol

The bitterness of 10 different products with ambroxol as active ingredient, the original and nine generics, were evaluated by human gustatory sensation tests in which the tablets were kept in the mouth, with water, at 20 and 37°C. The products all showed different bitterness intensities. The original and some of the generic products had comparatively low bitterness intensities but some of the generic products had comparatively high bitterness intensities. The bitterness intensities of these 10 was found to be significantly correlated with both the disintegration time, as evaluated using the ODT-101 (a recently developed apparatus), and the drug concentration in dissolved medium, as measured in a conventional dissolution test. The bitterness threshold of ambroxol solution was found to increase when the temperature of the water with which the tablets were taken, was raised from 20 to 37°C. The equation was calculated to predict the bitterness intensity of ambroxol, a function based on temperature and the ambroxol concentration using data from a standard ambroxol solution at 4, 20 and 37°C. The bitterness intensities obtained for the 10 ambroxol formulations with water at 20 and 37°C, coincided with the bitterness values predicted by the equation.     

Assessment of bitter taste of pharmaceuticals with multisensor system employing 3 way PLS regression

The application of the potentiometric multisensor system (electronic tongue, ET) for quantification of the bitter taste of structurally diverse active pharmaceutical ingredients (API) is reported. The measurements were performed using a set of bitter substances that had been assessed by a professional human sensory panel and the in vivo rat brief access taste aversion (BATA) model to produce bitterness intensity scores for each substance at different concentrations. The set consisted of eight substances, both inorganic and organic – azelastine, caffeine, chlorhexidine, potassium nitrate, naratriptan, paracetamol, quinine, and sumatriptan. With the aim of enhancing the response of the sensors to the studied APIs, measurements were carried out at different pH levels ranging from 2 to 10, thus promoting ionization of the compounds. This experiment yielded a 3 way data array (samples × sensors × pH levels) from which 3wayPLS regression models were constructed with both human panel and rat model reference data. These models revealed that artificial assessment of bitter taste with ET in the chosen set of API's is possible with average relative errors of 16% in terms of human panel bitterness score and 25% in terms of inhibition values from in vivo rat model data. Furthermore, these 3wayPLS models were applied for prediction of the bitterness in blind test samples of a further set of API's. The results of the prediction were compared with the inhibition values obtained from the in vivo rat model.     

MEMBRANE POTENTIAL CAN INFLUENCE THE RATE OF MEMBRANE PHOTOMODIFICATION

Abstract— Though cellular photomodification has been shown to change cellular resting membrane potential, an effect of membrane potential on the rate of photomodification has never been reported. Here we demonstrate that the rate of photomodification of potassium channels in frog atrial cells is voltage dependent. The rate of potassium channel photomodification using negatively charged Rose Bengal as the photosensitizer is about 2.5 times greater at the resting membrane potential of -70 m V compared to +40 mV. Similar results are obtained using the positively charged photosensitizer methylene blue. On the other hand, the rate of photomodified increase of leak current in the same cells does not significantly change in this voltage range with Rose Bengal as photosensitizer, but demonstrates a voltage dependence like that of potassium current when methylene blue is the photosensitizer. These observations cannot be explained based on voltage-dependent partitioning of the sensitizer, as similar effects on potassium current were obtained using either a positively charged or negatively charged sensitizer.     

Recognition of bile acids at cyclodextrin-modified gold electrodes.

Lipoylamino-beta- and gamma-cyclodextrin (LP-beta-CD and LP-gamma-CD, respectively) were adsorbed at the surface of gold electrodes by sulfur-gold bonding. The resultant electrodes exhibited quasi-reversible voltammograms for the redox reaction of Fe(CN)6(3-/4-) in aqueous solutions, with peak-to-peak separation (deltaEp) being 85 mV at 20 mV s(-1) as a potential sweep rate. When bile acids are added to the solution, deltaEp values increased to 200-300 mV with increasing the concentration of bile acids. A Langmuir-type adsorption analyses satisfactorily afforded the binding constants (Ksurf) of the surface-confined LP-beta-CD and LP-gamma-CD with the bile acids. The obtained Ksurf values of LP-gamma-CD are 5.0-50 times larger than the corresponding binding constants of gamma-CD in homogeneous aqueous solutions. Cyclic voltammetric experiments with positively, negatively, and non-charged adamantane derivatives as well as pH titration experiments revealed that the retardation of the electrode reaction of negatively charged Fe(CN)6(3-/4-) caused by bile acids was attributable (1) to electric potential changes due to the accumulation of the negative charges at the electrode surface, and (2) to an increase in the hydrophobicity of the electrode surface due to the binding of hydrophobic bile acids to the LP-beta-CD and LP-gamma-CD membranes.     

Suppression of bitterness and improvement of palatability of commercial prednisolone powder

The aim of the study was to suppress the bitterness and improve the palatability of pediatric prednisolone powder (PP) by the addition of simple sucrose syrup (SS) and various beverages and foods. Bitterness suppression was evaluated using the human gustatory sensory test. The suppression of the bitterness and improvement of palatability of PP by addition of SS solutions was investigated using standard taste substances: sucrose for sweetness, tartaric acid for sourness, and sodium chloride as saltiness. Dilution with SS solutions of up to 50% (w/w) was successful in bitterness-suppression and improvement of palatability, but at 80% (w/w) SS, the palatability of the diluted solution was reduced. The kinematic viscosities of SS solutions were therefore evaluated using the Uberorde viscosity meter, to see whether the high viscosity of the more concentrated solutions was responsible for the reduced palatability. The kinematic viscosity of the 80% SS was 16.60 mm(2)/s. Judging from above information, the palatability might become worse when the kinematic viscosity of syrup exceeded 15 mm(2)/s. Finally, the ability of various beverages and foods with low viscosity to suppress the bitterness and improve the palatability of PP were examined. The additions of orange juice or a carbonated lemon drink to simple syrup solution were most effective in suppressing bitterness and improving palatability of PP.