Study on the mechanism of oxidation of soybean oil in O/W 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%(V∶V)soybean oil,0.5-1.0 mM EDTA,and 1%(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 mM citrate-phosphate(pH 4.0)or 25 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 the.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.