Coating oil droplets with rice proteins to control the release rate of encapsulated beta-carotene during in vitro digestion

Abstract

Food protein-based delivery systems have unique advantages. Herein, a facile one-step fabrication of oil droplets with a tunable release rate of encapsulated lipophilic compounds during in vitro digestion is reported. Modified rice proteins (MRPs) were deposited on oil droplets with a thickness controllable by the final pH during titration of an alkaline solution of MRPs blended with oil, resulting from significant changes of secondary structures and solubility of MRPs at pH 6.0–7.0. Oil droplets were smaller than 400 nm, and the tunable conformation of MRPs and therefore resistance against peptic and pancreatic digestions resulted in the release rate of encapsulated β-carotene controllable by shell structures formed during titration. The irregular aggregates at pH 6.2 resulted in the step release of encapsulated β-carotene, releasing ca. 25% and 100%, respectively, at the simulated gastric and intestinal conditions. Whereas, the release of β-carotene was limited at the simulated gastric conditions but followed the zero-order kinetics at the simulated intestinal conditions, with a higher release rate for oil droplets with thinner shells produced at a higher pH between 6.4 and 7.0. Therefore, novel emulsion-based delivery systems can be fabricated with MRPs to control release profiles of lipophilic compounds during digestion.