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

Abstract

Bioactive polyphenols are important anti-cancer phytochemicals in natural materials. It is essential to develop a cost-effective technology to enrich bioactive polyphenols from their leaching liquor and maintain their stability. In this study, a novel microbubble-foam fractionation technology was developed to effectively separate a bioactive polyphenol from its diluted solution. Caffeic acid (CA) was considered as a structure-representative bioactive polyphenol without foaming capacity. Whey soy protein (WSP), a natural surfactant prepared from a waste soymeal, was used as both a collector and a frother. Microbubbles were introduced for enhancing the interfacial adsorption of WSP. The nitrogen was sparged through the gas distributor to form normal bubbles in the liquid phase. With the coalescence between microbubbles and normal bubbles, CA was successfully embedded in WSP and adsorbed on the surface of final bubbles and finally concentrated in the foamate. The fluorescence and reductive capacity results indicated that CA was successfully embedded in WSP, and the WSP aggregation on the bubble interface maintained the antioxidant properties of CA in a concentrated solution. Besides, their interactions could be significantly influenced by pH. Then, in the concentrated solution, CA could be easily purified from WSP. The enrichment ratio and recovery percentage of CA reached 20.0 and 73.9% under the optimal operating conditions, respectively. The reuse of WSP and the pilot-scale microbubble foam fractionation demonstrated the feasibility of the technology using in the separation process of bioactive polyphenols.