Three kinds of excipients were selected to investigate the anti-bitterness effect on the extremely bitter characteristics of Andrographis Herba decoction, and the optimal combined anti-bitterness formula was obtained. The preparation principle of different excipients was clarified by virtual screening and experimental verification to explore the advantages of the three kinds of excipients in the combined anti-bitterness effect. Sensory evaluation showed that mPEG_(2000)-PLLA_(2000), γ-cyclodextrin(γ-CD), and aspartame all had good anti-bitterness effect, which reduced the bitterness intensity of Andrographis Herba decoction by 0.5, 6, and 3 points, respectively. The anti-bitterness effect was superior when 0.15% mPEG_(2000)-PLLA_(2000), 1.60% γ-CD, and 0.04% aspartame were combined, and the taste score of the Andrographis Herba decoction decreased from 8 points(severe bitterness) to 1 point(almost no bitterness). Quantum chemistry calculations showed that mPEG_(2000)-PLLA_(2000) reduced the electrostatic potential of bitter groups, which spontaneously combined with it and formed a physical barrier, hindering the binding of bitter components to receptors. The interaction between γ-CD and bitter components was studied. It was found that the surface area and free energy of γ-CD decreased and the dipole moment increased, indicating that γ-CD included bitter components and self-assembled to form supramolecules. Molecular docking showed that hydroxy at position 14 and carbonyl at position 16 of andrographolide, and hydroxy at position 3 and 4, carbonyl at position 14, and five-membered lactone ring of dehydrated andrographolide were possibly the main bitter groups. The binding free energies of aspartame to bitter receptors TAS2 R10, TAS2 R14, and TAS2 R46 were-3.21,-1.55, and-2.52 kcal·mol~(-1), respectively, indicating that aspartame competed to inhibit the binding of bitter groups to bitter receptors. The results of content determination showed that the free amounts of andrographolide and dehydrated andrographolide in Andrographis Herba decoction were 0.23% and 0.28% respectively, while after adding flavor masking excipients, the dissociation amount of andrographolide and dehydrated andrographolide in the decoction decreased to 0.13% and 0.20%, respectively. The above results show that mPEG_(2000)-PLLA_(2000) involves some bitter components into it through micellar self-assembly to reconcile the entrance bitterness, and γ-CD includes the remaining bitter components in the real solution to control the main bitter taste. Aspartame further competes to inhibit the combination of bitter components and bitter receptors, and improves the taste to be sweet. Multi-excipients combined with anti-bitterness strategy significantly reduces the free concentration of bitter substances in Andrographis Herba decoction, and optimizes the taste of the decoction.
Keywords: Andrographis Herba; bitter taste; masking taste; traditional Chinese medicine decoction companion.