Tailoring zein nanoparticle functionality using biopolymer coatings: Impact on curcumin bioaccessibility and antioxidant capacity under simulated gastrointestinal conditions

Protein nanoparticles can be used to encapsulate, protect, and deliver hydrophobic bioactive agents however, they are often unstable to environmental stresses. In this study, the impact of electrostatic deposition of a biopolymer coating (alginate/gelatin) on the physicochemical and functional properties of curcumin-loaded zein nanoparticles was determined. The pH stability of the zein nanoparticles was greatly improved by the biopolymer coatings, with a 7:3 w/w alginate-to-gelatin ratio being the most effective at inhibiting particle aggregation from pH 3 to 7. The optimized biopolymer-coated nanoparticles remained stable to aggregation during long-term storage, and were resistant to heat treatment at 80 °C for up to 40 min in 10% aqueous sucrose solutions (pH 4.5). The in vitro bioaccessibility of curcumin was appreciably higher (22.4%) when it was encapsulated within biopolymer-coated zein nanoparticles than when it was not encapsulated (<8%). This effect was mainly attributed to the ability of the nanoparticles to inhibit curcumin degradation and increase curcumin solubility within the simulated gastrointestinal tract (GIT). The in vitro antioxidant capacity of curcumin after exposure to the simulated GIT was also greatly improved by encapsulation within the nanoparticles, as demonstrated by much stronger ABTS+· radical scavenging and ferric ion reducing power. These results suggest that biopolymer-coated zein nanoparticles may be an effective oral delivery system for curcumin that could be used in functional foods or beverages.