Application of starch nanoparticles as host materials for encapsulation of curcumin: Effect of citric acid modification

To encapsulate curcumin, absolute ethanolic curcumin solution with various content (300-1200 μg) was added to aqueous dispersion of citric acid-modified starch nanoparticles (M.SNPs) with various contents (0.5-2.5%), and then ethanol of the mixture was evaporated by nitrogen gas purge for 40 min (ethanol content decreased to 1%). SNPs (100 mg) could encapsulate 75.7 μg of curcumin in matrices of the composite, while 100 mg of M.SNPs could encapsulate 144.9 μg of curcumin. The XRD results revealed that curcumin was amorphously encapsulated in the composite, and hydrogen bond formation between M.SNPs and curcumin was one of the major driving forces for encapsulation as suggested by FT-IR. The composites had a spherical shape and mean particle size of the composites was increased from 136.3 to 255.3 nm with higher curcumin content in the matrices of composites. UV, pH, and thermal stability of curcumin significantly enhanced by the encapsulation, which was further increased when using M.SNPs and/or higher content of host materials. For the release of curcumin in simulated intestinal fluid digestion, release mechanism explained by Korsmeyer-Peppas model. For M.SNPs, k value was decreased from 13.097 to 2.938 as addition level of host material increased from 0.5 to 2.5%.