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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Two sweet potato varieties, deep orange color (Mun-kai) and deep purple color (Negro) were purchased from a local market. The roots were prepared into two starch samples: orange flesh starch (OS) from Mun-Kai variety and purple flesh starch (PS) from Negro variety. The starch extraction process was performed according to the methods of Wiersema [7] with a slight modification. Sweet potatoes were washed with tap water, manually peeled, diced into 2-3 cm cubes, soaked in 0.3% potassium metabisulfite for 5 min, and thoroughly minced at a low speed using a Waring blender (Model 32BL80, Waring commercial, New Hartford, CT) for 2 min. The resulting starch slurry was filtered through a cloth bag (about 80mesh) and sieved through a 120-mesh sieve. The filtrate was collected and allowed to stand undisturbed for 3-5 h.The effects of blanching on physicochemical properties of flours and starches prepared from two varieties of sweet potatoes (Mun-Kai and Negro) were studied and compared. The pasting temperature and peak viscosity of starches, respectively, were 74 and 80 °C and 381 and 433 RVU. The pasting temperature (74.0-94.8 °C) of flours was greater than that of starch, depending on the variety and blanching process. However, the peak viscosity (ca. 103-120 RVU) of flours was lower than that of the corresponding starches. Partial gelatinization of starch granules was observed as a result of a 1-min blanching. Composition of starch and flour was found to affect swelling power and solubility. The starch content of starches, flours from unblanched sweet potato and flours from 1-min blanched sweet potatoes were 97; 66.3 and 74.9; as well as 36.6 and 40.4%, respectively. Amylose content of flours and starches varied from 17.2-20.8%.

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