| Oxidation is a leading cause for quality deterioration and loss of nutrients in lipid-containing foods. Both bulk oils and their dispersed emulsions are known to be susceptible to oxidation. However, for lipids in a micelle system, the oxidation mechanism remains controversial. The objective of this study was to examine the effect of emulsifier type, pH, EDTA and particle size on the oxidation of soybean oil in O/W emulsions.Firstly, the visual-spectrophotometry method for peroxide value of oil-in-water emulsions was studied. The determination conditions, precision, accuracy and influencing factors of the method were discussed in detailed. The results showed that, when the concentration of Fe3+ was in the range of 04.0mg/L, the relationship between absorbance at 510nm and concentration of Fe3+ -thiocyanate complex compound accords with the Lambert & Bill's law. The relative standard deviation was 0.60%. The rates of recovery were 98.2%101.2%. The limited detection POV was 1.701meq/kg. The results indicate that this method can provide high precision and accuracy and low cost of reagents. This method is suitable for hydroperoxides analysis of oil-in-water emulsions.The effect of emulsifier type, pH, EDTA and particle size on the oxidation of soybean oil in O/W emulsions was studied in this paper. O/W emulsions were prepared with 25.0% (v/v) soybean oil, 0.50-1.00 mM EDTA, and 1.0% (v/v) anionic (SDS; DBS), cationic (CTAB; CPBM), or nonionic (sorbitan monolaurate, Span20; polyoxyethylene sorbitan monolaurate, Tween 20; sugar ester, SE-15) emulsifiers in 25.0 mM citrate-phosphate (pH 4.0) or 25.0 mM phosphate (pH 7.0 and 9.0) buffer. The emulsions were stored at 37°C and auto-oxidation was monitored by measuring peroxide value (POV). Emulsions stabilized by SDS had the highest lipid oxidation rate compared with those stabilized by cationic and nonionic emulsifiers at pH 4.0, while CTAB-stabilized emulsions oxidized the most rapidly under pH 7.0 and 9.0. The addition of EDTA to Tween 20-stabilized emulsions greatly suppressed (p< 0.05) the lipid oxidation. Droplet size distribution was influenced by emulsifier content and showed with the decreasing of diameter the oxidation of the O/W emulsions incereased. The results indicated that oxidative stability of soybean oil in O/W emulsions was critically affected by the emulsifier types and then an optimum oxidative stability can be achieved through controlling the pH of the continuous phase of the emulsion and the addition of proper metal ion chelators.The oxidation kinetics of the Tween20 stabilized soybean oil emulsion was studied. In the range of 50-65℃, the temperature coefficient (Q10) is about 2.7, the reaction activation energy (E) is 74910.8028 kJ/mol, the frequency factor (K0) is 1.644×1010. By regression linear analysis, the relationship between temperature and oxidation speed was deduced. |
