Caffeic acid grafted chitosan as a novel dual-functional stabilizer for food-grade emulsions and additive antioxidant property

The aim of this study was to develop a novel dual-functional stabilizer for food-grade Pickering emulsions by grafting caffeic acid onto chitosan via a free radical mediated method. The grafting of caffeic acid onto chitosan was confirmed by UV-vis absorption spectra, FTIR spectra and H-1 NMR spectra and DSC thermogram. The antioxidant properties of the caffeic acid grafted chitosan (CA-g-Ch) were measured by three in vitro assays. Caffeic acid-grafted chitosan displayed much better Fe2+ chelating property than both chitosan and caffeic acid, and retained comparable DPPH radical scavenging activity as caffeic acid. Moreover, the formation of the CA-g-Ch based emulsion was monitored by the turbidity, zeta potential, and particle size measurements. The CA-g-Ch polymers were found to be pH-responsive. The oil (linoleic acid) in water emulsions with the CA-g-Ch (as emulsifier/Pickering stabilizer) was prepared to examine its potential to stabilize Pickering emulsions, as well as its additive antioxidant properties. The results (zeta potential, mean droplet size, creaming index and TBARS values etc) demonstrated that the CA-g-Ch could act as a dual-functional stabilizer for Pickering emulsions. The emulsions made with the CA-g-Ch were found to be stable at a broad pH range of 3-6. Our findings proved that CA-g-Ch as novel dual-functional polymeric surfactant, may have great potential to find applications in food and pharmaceutical industries.