High-efficiency foam fractionation of anthocyanin from perilla leaves using surfactant-free active Al₂O₃ nanoparticle as collector and frother: Performance and mechanism

Anthocyanin (ACN) is a natural pigment with significant industrial applications. However, foam fractionation of ACN from perilla leaves extract presents theoretical challenges due to its limited surface activity and foaming capacity. This work developed a surfactant-free active Al2O3 nanoparticle (ANP) as a collector and frother, which was modified with adipic acid (AA). The ANP-AA efficiently collected ACN through the electrostatic interaction, condensation reaction, and hydrogen bonding, with a Langmuir maximum capacity of 129.62 mg/g. Moreover, ANP-AA could form a stable foam layer by irreversibly adsorbing on the gas-liquid interface, reducing surface tension, and alleviating liquid drainage. Under the appropriate conditions of ANP-AA 400 mg/L and pH 5.0, we achieved a high ACN recovery of 95.68% with an enrichment ratio of 29.87 after ultrasound-assisted extraction of ACN from perilla leaves. Additionally, the recovered ACN displayed promising antioxidant properties. These findings hold significant importance in the food, colorant, and pharmaceutical industries.