The objective of this research was to evaluate the influence of storage pH (3 and 7) and biopolymer emulsifier
type (Whey protein isolate (WPI), Modified starch (MS) and Gum arabic (GA)) on the physical and
oxidative stability of rice bran oil-in-water emulsions. All three emulsifiers formed small emulsion droplets
(d32 < 0.5 lm) when used at sufficiently high levels: 0.45%, 1% and 10% for WPI, MS and GA, respectively.
The droplets were relatively stable to droplet growth throughout storage (d32 < 0.6 lm after
20 days), although there was some evidence of droplet aggregation particularly in the MS-stabilized
emulsions. The electrical charge on the biopolymer-coated lipid droplets depended on pH and biopolymer
type: 13 and 27 mV at pH 3 and 7 for GA; 2 and 3 mV at pH 3 and 7 for MS; +37 and
38 mV at pH 3 and 7 for WPI. The oxidative stability of the emulsions was monitored by measuring peroxide
(primary products) and hexanal (secondary products) formation during storage at 37 C, for up to
20 days, in the presence of a pro-oxidant (iron/EDTA). Rice bran oil emulsions containing MS- and WPIcoated
lipid droplets were relatively stable to lipid oxidation, but those containing GA-coated droplets
were highly unstable to oxidation at both pH 3 and 7. The results are interpreted in terms of the impact
of the electrical characteristics of the biopolymers on the ability of cationic iron ions to interact with
emulsified lipids. These results have important implications for utilizing rice bran oil, and other oxidatively
unstable oils, in commercial food and beverage products.