Optimisation of the adsorption of polyphenols from Inga edulis leaves on macroporous resins using an experimental design methodology

Adsorption on macroporous resins was tested as a means of purifying the phenolic compounds from crude extracts of Inga edulis leaves. The experimental design methodology was used to optimise this process. The variables tested were the water proportion (50, 70 and 90%; v/v) in the hydroalcoholic extract solution, its pH value (2.0, 3.5 and 5.0) and the type of adsorbent used (XAD-7, XAD-16, EXA-90 and EXA-118). The time of contact was fixed at 2 h on the basis of kinetic studies. Statistically significant differences (p < 0.05) were obtained for the water proportion and the type of adsorbent, whereas the pH of the extract had no influence on the efficiency of adsorption. In all conditions, the XAD-7 resin gave the best results, reaching 239 mg equivalent phenolics per gresin, and XAD-16 the worst ones. Sorption isotherms were constructed for these two resins under optimal ethanol conditions and fitted well to the Freundlich and Langmuir models (R2 > 0.95). The optimized results will be used in the design of fixed-bed adsorption systems for the purification and concentration of phenolic compounds from I. edulis leaves.