Effectively recovering catechin compounds in the removal of caffeine from tea polyphenol extract by using hydrophobically modified collagen fiber

Previous research had proved that collagen fiber can be used as separation material for removing caffeine from tea polyphenol extract effectively. But the recovery rate of catechin compounds from collagen fiber column was quite low by using water and ethanol as eluent because of excessively strong hydrogen bond interaction between collagen fiber and polyphenols. To solve the problem, collagen fiber was hydrophobically modified in this work by using silane coupling agents with alkyl chains (butyl, octyl, dodecyl and octadecyl). FT-IR, DSC, SEM and EDS Mapping proved the successful grafting of alkyl chains on collagen fiber, leading to the significantly enhanced hydrophobicity of collagen fiber. Static adsorption showed that the adsorption capacity of EGCG decreased when the grafted alkyl chain length increased mainly relying on the weakened hydrogen bond interaction. Dynamic adsorption and elution behavior also indicated less retention capacity of EGCG on collagen fiber with higher hydrophobicity. In column separation of simulated tea polyphenol extract containing caffeine and catechin compounds, the collagen fiber grafted with octadecyls (CF(C18)) presented excellent separation efficiency for caffeine and catechin compounds, and simultaneously the catechin compounds were highly recovered. The recovery rates of EGC and EGCG were 2–7 times higher than those separated by pristine collagen fiber column and glutaradehyde crosslinked collagen fiber column developed in our previous work. In the reusing round of CF(C18) column, the chromatogram was almost the same as the first round, showing excellent reusability. In fact, the separation performance of CF(C18) to caffeine and catechin compounds was comprehensively superior to Sephadex LH-20, presenting great practical application potential in effectively removing caffeine from tea polyphenol extract and recovering catechin compounds.