Foam fractionation of rosmarinic acid from perilla leaves using surface-modified Al2O3 nanoparticle as frother and collector

Nowadays, developing an efficient, economical, and sustainable method for separating bioactive phytochemicals from plants extracts has gained increasing attention. Rosmarinic acid (RA) with potent biological activities was successfully isolated by foam fractionation from the extract of perilla ( Perilla frutescens L.) leaves. To achieve the adsorption of RA without surface activity on the stable air-water interface, γ-Al 2 O 3 nanoparticles (ANPs) modified by cocamidopropyl betaine (CAPB) were prepared and used as the nano-frother and nano-collector. After optimization of water extraction of RA, ANP–CAPB was characterized by SEM-EDS, FTIR, XPS, surface charge, and hydrophobicity analyses. The effects of ANP-CAPB with various modified degrees on the foam property and collection property were examined systematically. On the one hand, ANP-CAPB was colloidally stable, and it could generate stable foams due to the introduction of hydrophobic chains on the ANP surface. On the other hand, ANP-CAPB displayed excellent collection towards RA, and the adsorption kinetics and isotherm of this process followed the pseudo-second-order model and Freundlich model, respectively. Moreover, reasonable mechanisms were proposed to elucidate the modification and adsorption behavior. Under the suitable conditions of 400 mg/L ANP-CAPB and pH 5.0, the enrichment ratio and the recovery percentage of RA were 59.07% and 93.33%, respectively. Furthermore, the RA product showed promising antioxidant potential and significant antibacterial activity. This work not only described an efficient foam fractionation for RA isolation, but it also offered valuable clues for the separation study of other plant extracts.