Rheology, stability, antioxidant properties, and curcumin release of oil-in-water Pickering emulsions stabilized by rice starch nanoparticles

Modification of rice starch nanoparticles (SNP) as an emulsifier in Pickering emulsions is reported in this work. The SNP was prepared by HCl hydrolysis with different resident times and subsequently modified via crosslinking by citric acid using various crosslinking times to improve the hydrophobicity of SNP. The modified SNP was used to prepare sunflower oil-in-water Pickering emulsions loaded with curcumin. The optimal hydrolysis conditions (2.2 M HCl, 6 days) produced SNP with a 21.87 ± 0.69 % yield and 45.56 ± 0.00 % crystallinity. The citric acid-modified SNP with a 6-h crosslinking period (SNP-M-6 h) had a water contact angle of 87.2°. The suitable Pickering emulsion containing 30 wt% curcumin-loaded sunflower oil was stabilized by 3.0 wt% SNP-M-6 h. This Pickering emulsion had shear thinning properties with a pseudoplastic fluid behavior and was characterized by a droplet size of 47.16 ± 4.22 μm with a high degree of stability over five weeks of storage. Furthermore, the curcumin release from the emulsion depended on the pH, and curcumin could maintain its free radical scavenging quality. A very beneficial property of the Pickering emulsion is that it can slowly release curcumin at low pH, but more rapid release at higher pH, making it a potentially excellent candidate for drug delivery through oral intake.