Rice bran oil (RBO) is used in foods, cosmetics, and pharmaceuticals due to its desirable health, flavor, and functional attributes. We investigated the effects of biopolymer emulsifier type and environmental stresses on the stability of RBO emulsions. Oil-in-water emulsions (5% RBO, 10 mM citrate buffer) stabilized by whey protein isolate (WPI), gum arabic (GA), or modified starch (MS) were prepared using high-pressure homogenization. The new MS used had a higher number of octenyl succinic anhydride (OSA) groups per starch molecule than conventional MS. The droplet diameters produced by WPI and MS were considerably smaller (d < 300 nm) than those produced by GA (d > 1000 nm). The influence of pH (3 to 8), ionic strength (0 to 500 mM NaCl), and thermal treatment (30 to 90 °C) on the physical stability of the emulsions was examined. Extensive droplet aggregation occurred in WPI-stabilized emulsions around their isoelectric point (4 < pH < 6), at high salt (> 200 mM, pH 7), and at high temperatures (>70 °C, pH 7, 150 mM NaCl), which was attributed to changes in electrostatic and hydrophobic interactions between droplets. There was little effect of pH, ionic strength, and temperature on emulsions stabilized by GA or MS, which was attributed to strong steric stabilization. In summary: WPI produced small droplets at low concentrations, but they had poor stability to environmental stress; GA produced large droplets and needed high concentrations, but they had good stability to stress; new MS produced small droplets at low concentrations, with good stability to stress. Practical Application: This study showed that stable rice bran oil-in-water emulsions can be formed using biopolymer emulsifiers. These emulsions could be used to incorporate RBO into a wide range of food products. We compared the relative performance of whey protein, GA, and a new MS at forming and stabilizing the emulsions. The new OSA MS was capable of forming small stable droplets at relatively low concentrations.

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The ability of rice protein supplemented with various prebiotics to protect probiotic Lactobacillus plantarum TISTR 2075 upon freeze-drying and subsequent storage was determined. A combination of rice proteinfructooligosaccharide (RF) provided the best storage stability with the lowest specific rate of cell death (k) of 1.20 9 10-2 and 5.79 9 10-2 1/day during subsequent storage at 4°C for 180 days and 30°C for 90 days, respectively. Glass transition temperatures (T g) of freezedried probiotic in various protectants were 14.2-25.4 and 42.9-50.1°C after storage at 4 and 30°C, respectively. The functional properties of freeze-dried probiotic with protectants remained stable. The presence of RF could effectively protect and enhance the probiotic functionality during exposure to gastrointestinal tract conditions. The pathogenic inhibition of freeze-dried probiotic against foodborne pathogens was not different from the active cells. Protective agents were able to maintain high degrees of cell surface hydrophobicity.

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