Comparison of four analytical methods for the determination of peroxide value in oxidized soybean oils

Previous work in our laboratory demonstrated that soybean oil oxidation, expressed as PV, can be determined using NIR transmission spectroscopy as an alternative to the official AOCS iodometric titration method. In the present study, a comparison of four peroxide analytical methods was conducted using oxidized soybean oil. The methods included the official AOCS iodometric titration, the newly developed NIR method, the PeroxySafe^™ kit, and a ferrous xylenol orange (FOX) method, the latter two being colorimetric methods based on oxidation of iron. Five different commercially available soybean oils were exposed to fluorescent light to obtain PV levels of 0–20 meq/kg; periodic sampling was done to ensure having representative samples throughout the designated range. A total of 46 oil samples were analyzed. Statistical analysis of the data showed that the correlation coefficient (r) and standard deviation of differences (SDD) between the standard titration and NIR methods were r=0.991, SDD=0.72 meq/kg; between titration and the PeroxySafe^™ kit were r=0.993, SDD=0.56 meq/kg; and between the standard titration and FOX method were r=0.975, SDD=2.3 meq/kg. The high correlations between the titration, NIR, and PeroxySafe^™ kit data indicated that these methods were equivalent.