Evaluation of bitterness in mother tinctures by an electronic tongue: impact of cyclodextrin complexation

Abstract

The pronounced bitterness of herbal mother tinctures often limits their palatability, despite their therapeutic value. This study evaluates the effectiveness of different cyclodextrins (CDs) in masking the bitterness of five herbal tinctures (marrubium, propolis, thyme, plantain and eucalyptus) using an α-Astree II electronic tongue equipped with seven potentiometric sensors.

Highlights

Several types of cyclodextrins were used to mask bitterness in herbal mother tinctures.
Efficiency of taste-masking was assessed using an e-tongue analysis combined with PCA.
The efficacy of CDs in reducing perceived bitterness depended on the mother tincture.
Inclusion complexation of the highly bitter marrubiin in β-CD was shown by GC-MS.

The bitterness-masking abilities of β-CD, methylated β-CD, and hydroxypropyl β– and γ-CDs (HP-β-CD and HP-γ-CD) were investigated by applying a Principal Component Analysis (PCA) to the e-tongue data. Caffeine was used as a standard bitter reference providing the direction of bitterness in the PCA space. The e-tongue analysis does not allow a quantitative assessment of bitterness, and of taste in general. The addition of CDs reduces the perceived bitterness of tinctures.

The efficacy depended on the types of CD and mother tincture; β-CD was the most effective in reducing bitterness of marrubium mother tincture. Complementary GC-MS analysis confirmed the formation of an inclusion complex of β-CD and the highly bitter molecule, marrubiin, present in the marrubium mother tincture. These results validated the electronic tongue system for the evaluation of bitter taste masking in complex phytopharmaceutical plant extracts.

Results and discussion

The taste of the mother tinctures was investigated using the e-tongue before and after complexation with cyclodextrin. Four types of cyclodextrin were used in order to reduce the bitterness of the herbal mixtures: β-cyclodextrin (β-CD), methylated β-CD (CRYSMEB-β-CD), and hydroxypropyl β– and γ-CDs (HP-β-CD and HP-γ-CD, respectively). The structure and some physicochemical properties of the CDs used are presented in Fig. 1 and Table 1.

Jihen Kallel, Salwa Ben Aissa, Basma Ousji, Yves Chevalier, Souhaira Hbaieb, Claire Bordes, Evaluation of bitterness in mother tinctures by an electronic tongue: impact of cyclodextrin complexation, International Journal of Pharmaceutics, Volume 686, 2025, 126345, ISSN 0378-5173, https://doi.org/10.1016/j.ijpharm.2025.126345.