Adsorption and desorption characteristics of polyphenols from Eucommia ulmoides Oliv. leaves with macroporous resin and its inhibitory effect on α-amylase and α-glucosidase

Background: Eucommia ulmoides Oliv. (EUO) was a traditional Chinese herb, its leaves were abundant in China, and polyphenol compounds were considered to be an important active ingredient in Eucommia ulmoides Oliv. leaves (EUOL). However, previous research mainly focused on compound identification and extraction process, there were few reported on the efficient enrichment process and biological activity evaluation of polyphenols in EUOL. Methods: The adsorption and desorption characteristics of twelve different resins (HPD-1(X), HPD-300, HPD-600, D-3250, X-5, D-140, NKA-9, NKA-II, D-101, AB-8, S-8 and Polyamide) were investigated to develop an efficient method for the enrichment of polyphenol from EUOL, and the static adsorption, kinetics, isotherm and thermodynamics of the polyphenol from EUOL, were analyzed. The eluted component was obtained through dynamic elution, and its main polyphenol compounds were detected by high-phase liquid chromatography (HPLC) and the inhibitory effects on the enzyme activity of alpha-amylase and alpha-glucosidase was also evaluated for different elution components. Meanwhile, the binding of main polyphenol compounds to enzyme was also evaluated. Results: The selected resins (HPD-300, HPD-600, D-3250, X-5, D-140, NKA-9, D-101 and AB-8) showed adsorption patterns that fitted well to the pseudo second-order kinetics. The intra-particle diffusion model demonstrated that the diffusion of polyphenol compounds on these resins were divided into three processes. For HPD-300, HPD-600 and NKA-9, the Freundlich model better described the adsorption isotherm behavior than the Langmuir model, and the adsorption of polyphenol was a physical, exothermic, and spontaneous process. Subsequently, dynamic elution was performed yielding a higher polyphenol content in a 60% ethanol-water elution component, and it also exhibited a higher inhibitory effect on alpha-amylase and alpha-glucosidase activity. Furthermore, as the main polyphenol compounds, chlorogenic acid, rutin, quercetin and kaempferol were used to simulate the binding to the enzyme protein through molecular docking technology. The results showed that quercetin had a higher docking score for alpha-amylase, while rutin displayed superior binding to alpha-glucosidase. Conclusions: Therefore, polyphenols of EUOL could be enriched through macroporous resins and have the potential to be effective enzyme inhibitor.