The Physical Characterization and Sorption Isotherm of Rice Bran Oil Powders Stabilized by Food-Grade Biopolymers

Rice bran oil (RBO) is used in several products in the food, cosmetics, and pharmaceutical industries due to its desirable health, flavor, and functional attributes. The formation and physicochemical properties of microencapsulated RBO stabilized by different biopolymers were investigated. Oil-in-water emulsions (10% RBO, citrate buffer pH 7) stabilized by either 3.5% whey protein isolate (WPI) or 7.0% modified starch (MS) containing maltodextrin (DE18) as a carrier agent were initially prepared. The diameter of emulsion droplets produced by WPI and MS were considerably smaller than 300 nm and 25 μm for dried particles. The resulting powders had poor to fair flowability and high cohesiveness characteristics: Carr index (27–37) and Hausner ratio (1.4–1.6). The microencapsulation efficiency of the spray-dried powders ranged from 92–95%. Moisture sorption isotherms of the powders were determined by a gravimetric method, while their glass transition temperatures (T_g) were determined by differential scanning calorimetry. The experimental water adsorption data were fitted to BET and GAB models. The GAB model fitted better the measured moisture isotherm than the BET model (R² = 0.99). Powders produced with MS showed higher water adsorption than those stabilized by WPI. Powders produced with WPI had a higher glass transition temperature than those produced with MS. Measurements of lipid deterioration in the RBO powder during storage showed that the reaction order was different for WPI-stabilized (n = 1) and MS-stabilized (n = 0) RBO powder. These results have important consequences for the creation of food-grade powders containing functional lipids such as RBO application.