Load mechanism and release behaviour of synephrine-loaded calcium pectinate beads: Experiments characterizations, theoretical calculations and mathematical modeling

It is an appropriate strategy to construct the carrier material with polysaccharide pectin, which is the characteristics of good bio-compatible, safe and non-toxic, avoiding the functional loss of bioactive ingredients and achieve sustained release. However, the loading mechanism of the active ingredient and the release behaviour of the active ingredient from the carrier material is still at the stage of conjecture. In this study, a kind of synephrine-loaded calcium pectinate beads (SCPB) with high encapsulation efficiency (95.6 %), loading capacity (11.5 %) and excellent controlled release behaviour was constructed. The interaction between synephrine (SYN) and quaternary ammonium fructus aurantii immaturus pectin (QFAIP) was revealed by FTIR, NMR and density functional theory (DFT) calculation. An inter-molecular hydrogen bond and Van der Waals forces between 7-OH, 11-OH and 10-NH of SYN and -OH, -C=O and N + (CH3)3 of QFAIP were formed. The release experiment in vitro showed that the QFAIP could effectively avoid the release of SYN in gastric fluid, and also realized the slow and full release of SYN in intestinal tract. Moreover, the release mechanism of SCPB in simulated gastric fluid (SGF) was Fickian diffusion, while in simulated intestinal fluid (SIF) was a non-Fickian diffusion controlled by both diffusion and skeleton dissolution.