Selective adsorption of tannins over small polyphenols on cross-linked polyacrylamide hydrogel beads and their regeneration with hot water

The uptake of a low dose of tannins shows health benefits. However, a high dose of tannins exhibits toxic effects. Herein cross-linked polyacrylamide hydrogel beads were prepared and used to remove or partially remove tannic acid , a model of tannins, from aqueous solutions (mimicking beverages) or alcohol-aqueous solutions (mimicking alcoholic beverages) while remaining most of the low molecular weight polyphenols such as epigallocatechin gallate (EGCG) and catechin, which are beneficial for health. The beads showed 4.1- and 77-fold higher adsorption capacities for tannic acid than for EGCG and catechin, respectively. The adsorption capacities and removal percentages were positively correlated with molecular weights of the polyphenols and hydrogen bonding alone was supposed to drive the adsorption. The adsorbed polyphenols were completely desorbed with hot water from the adsorbent, which can be attributed to the fact that elevated temperatures weakened or broken the hydrogen bonds .