Microbubble-foam fractionation enabled long-term caffeic acid stability in the separation process: Self-assembly WSP as collector

•Microbubble-foam fractionation was used to separate caffeic acid from its diluted aqueous solution.•WSP was used as bio-surfactant for the replacement of cationic surfactant.•The aggregation of WSP on foam interface could protect the stability of bioactive polyphenols.•Microbubbles were used as foam stabilizer to enhance the foam stability of protein.