Selective removal of caffeine from tea extracts using macroporous crosslinked polyvinyl alcohol adsorbents

Abstract

The hydrolysis reaction of ester groups in vinyl acetate (VAc) was used to introduce hydroxyl groups into the matrix of a macroporous adsorbent, which was itself prepared by free radical suspension copolymerization of triallyl isocyanurate (TAIC) and VAc. Therefore, the copolymerization incompatibility between the hydrophilic and the hydrophobic monomer was overcome successfully and the hydrophobic matrix of the polymeric adsorbent containing a polyvinyl alcohol (PVA) segment was obtained. Introduction of the PVA segment decreased the hydrophobic adsorption affinity of the adsorbent while producing the hydrogen-bonding interaction. When isolating the two active components, polyphenols (TPh) and caffeine (CAF), from green tea extracts, this polymeric adsorbent, namely poly(TAIC-co-VA), exhibited good adsorption selectivity towards TPh over CAF. The adsorption mechanism leading to this selectivity involved a hydrophobic interaction mechanism for CAF and multiple weak hydrophobic and hydrogen-bonding interactions for TPh. The adsorption thermodynamics for TPh on poly(TAIC-co-VA) were studied. The effects of adsorbent structure and gradient desorption conditions on isolation were investigated. The result showed that adsorbent, with 20% TAIC content, was able to efficiently remove CAF from different tea extracts with different ratios of TPh and CAF. Finally, almost no CAF was detected in the TPh fraction and the recovery of TPh was greater than 95%.

Amino-functionalized ordered mesoporous silica SBA-15, a rapid and efficient adsorbent for the adsorption of (−)-epigallocatechin gallate from green tea extract

“…The adsorption of EGCG is based on the hydrogen-bonding, whereas the adsorption of CAF is mainly driven by hydrophobic interactions. 14 Therefore, the design synthesis of adsorbent with different surface chemistry, which shows different interactions to EGCG and CAF, is very important for their high efficient separation and enrichment. Adsorbents with hydrogen-bonding groups (amine, amide, hydroxyl or carboxyl) could effectively adsorb EGCG, but not CAF based on the interaction mechanisms.…”

Adsorption chromatography separation of the flavonols kaempferol, quercetin and myricetin using cross‐linked collagen fibre as the stationary phase

“…, each flavonol consists of a hydrophobic backbone, and such a molecular structure provides the capability of hydrophobic interaction with the hydrophobic regions in collagen molecules. The competition of water molecules and flavonols in forming hydrogen bonds with GCF is enhanced at lower ethanol concentrations, which may lead to weaker absorption of flavonols on GCF . But the hydrophobic interactions of the flavonols with GCF would be gradually promoted as the ethanol concentration decreases from 60% to 30%.…”

Applying Box–Behnken Design for Formulation and Optimization of PLGA-Coffee Nanoparticles and Detecting Enhanced Antioxidant and Anticancer Activities

“…The insignificant increase of the TPC in PLGA-Cf-F 3 over that in PLGA-Cf-F 2 might be attributed to the physical adsorption of phenolic compounds by the surface-free alcoholic hydroxyl groups of PVA, through hydrogen bonding and hydrophobic interactions, rather than its encapsulation compared to the EE% and LC% of PLGA-Cf-F 2 NPs. Thus, these surface-bound phenolic compounds were easily desorbed, indicating a higher value, although it was not significant [ 54 ].…”