Purification and separation of caffeoyl spermidine derivatives from goji leaf tea with ion exchange resin and the mechanisms involved

Goji leaf (Lycium barbarum leaves, LBL) tea is a well-known beverage that has been developed and utilized for its numerous health benefits. Recently, we have successfully extracted four caffeoyl spermidines derivatives from LBL (LBLS), namely N-caffeoylputrescine, N-acetyl-N′-caffeoylputrescine, N₁-dihydrocaffeoyl-N₁₀-caffeoylspermidine and N₁, N₁₀-dicaffeoylspermidine. Given the diverse bioactivities exhibited by LBLS, our study aimed to develop a precise separation method and explore the possible purification mechanism. Firstly, the extraction process was optimized, followed by the selection of 001×7 resin for the enrichment and purification of LBLS from six resins. Subsequently, the adsorption mechanism was comprehensively examined using FT-IR, DSC, XRD, and XPS techniques. Additionally, investigations into the adsorption kinetics, isotherm models, and adsorption thermodynamics revealed the adsorption process of LBLS on 001×7 resin was spontaneous and exothermic, followed a monolayer adsorption mechanism, and conformed to the pseudo-second-order kinetic model and Langmuir model. The optimal procedure involved adsorbing a 25 mg/mL LBL extract onto a 3.5 BV (bed volume) at 2 BV/h, then eluting with an 8 % NaCl-55 % ethanol solution for 5 BV at the same rate. Finally, LBLS was separated using PHPLC to obtain monomer compounds. This process yields 1.57 %±0.1 % LBLS, and four monomers with purity range from 90.7 % to 100 % were obtained.