Adsorption of catechin onto cellulose and its mechanism study: Kinetic models, characterization and molecular simulation.

Catechin, an important component of flavan-3-ol, and dietary fiber are both important ingredients with many associated health benefits. The adsorption of catechin onto various dietary fiber has been studied widely, most of the researches focus on the adsorption capacities of catechin under different fibers and the adsorption types by using adsorption models. However, little is known on the dynamic adsorption process and mechanism, including the adsorption sites, interaction types, and participant molecules. In this study, the adsorption behavior and mechanism of catechin onto cellulose were examined by the time function in combination with molecular simulation. The adsorption capacities of cellulose for catechin were 2.70 and 2.82 mg/g at pH 2.0 and 7.0, respectively. The adsorption process was fitted by three stage models (rapid adsorption, saturation, and equilibrium). The features of cellulose and catechin were characterized by FTIR to identify the functional groups in the adsorption. Molecular simulation revealed that the catechin was adsorbed onto the hydrophilic surface of cellulose rather than hydrophobic one, and that the total binding energy was -8.57 kcal/mol of the hydrophilic surface, which was due to Van der Waals' force and H-bond more than electrostatic force. Furthermore, the studies on isothermal adsorption combined with adsorption at various pH illustrated the main interaction between cellulose and catechin for the binding. This work assisted understanding of the adsorption of polyphenols on to insoluble dietary fiber and has the potential of applications in functional foods.