Selective Separation of α-Punicalagin, β-Punicalagin, and Ellagic Acid from Pomegranate Husk Aqueous Extract by an Optimized Adsorption Process Employing a (Deep) Eutectic Solvent

Abstract

This research proposes an innovative and simplified adsorption/desorption method using renewable solvents to obtain punicalagin and ellagic acid–rich fractions from pomegranate husk. The type of adsorbents (PoraPak Rxn and Sepra C18-E), adsorbent mass (0.1, 0.2, 0.3, 0.4, and 0.5 g), adsorption temperature (20, 40, and 60 °C), pH of the extract (4, 6, and 8), and desorption solvents (a 1:2 betaine eutectic mixture and hydroalcoholic solutions) were evaluated. The optimized adsorption process involved 0.5 g of PoraPak Rxn and 7.5 mL extract at pH 4 and 20 °C for 5 min. Notably, PoraPak Rxn outperformed Sepra C18, exhibiting superior adsorption due to its favorable hydrophobic properties, porous structure, and affinity for the target compounds. The optimized method adsorbed 93% α-punicalagin, 95% β-punicalagin, and 100% ellagic acid. Betaine:glycerol at a 1:2 molar ratio was selected using COSMO-RS for desorption. The eutectic mixture with 50 wt.% water desorbed 91% α-punicalagin, 73% β-punicalagin, and 6% ellagic acid during the first three desorption cycles. Subsequent three desorption cycles using ethanol yielded a desorption of 62% ellagic acid free of punicalagins. This strategy of employing different desorption solvents proved efficient in recovering fractions with high concentrations of the desired compounds. Overall, this research demonstrates a promising approach for the efficient separation of punicalagins and ellagic acid from pomegranate husk extract.