Stoichiometric Determination of Hydroperoxides in Oils by Fourier Transform Near-Infrared Spectroscopy

A rapid Fourier transform near-infrared (FT-NIR) spectroscopic method was developed for quantitative determination of the peroxide values (PVs) of edible oils. The method is based on the stoichiometric reaction of triphenylphosphine (TPP) with hydroperoxides to produce triphenylphosphine oxide (TPPO). Calibration standards were prepared by adding randomized amounts of TPPO and TPP to peroxide-free high-erucic-acid rapeseed (HEAR) to produce a calibration matrix spanning the concentrations of TPPO and residual TPP in oils having PVs in the range 0-100 after complete reaction of the hydroperoxides with added TPP. A partial-least-squares (PLS) calibration model for predicting PV was developed by using the NIR spectral region from 4710 to 4540 cm-1, where TPP and TPPO both absorb. The resulting PLS calibration was linear, the cross-validation having a standard deviation (SD) of 1.36 PV over the analytical range. The method was validated by comparing the PLS-predicted PVs of oils spiked with tert-butyl hydroperoxide (TBHP) and those of naturally oxidized HEAR oils with the results obtained by using the American Oil Chemists’ Society (AOCS) iodometric procedure. The FT-NIR PV method correlated very well (SD = 1.20) with the reference AOCS method for TBHP-spiked oil samples. Similar results were obtained for naturally oxidized HEAR oil, with a standard deviation of the difference for reproducibility of ±1.11 PV for both methods. The analysis consists of adding about 0.04 mL TPP stock solution to 1 g oil, shaking, recording the spectrum, and using the PLS calibration to predict PV. Because of its simple and rapid stoichiometric reaction and its excellent correspondence to the iodometric method, the FT-NIR method provides a simple and alternative means of measuring PV. The FT-NIR method avoids the solvent and reagent disposal problems associated with the AOCS method and can be readily auto mated by appropriate programming of the FTIR spectrometer. Thus, it provides a simple and rapid analytical technique for determining PVs of fats and oils.

Accuracy of Peanut Moisture Determinations by Using the Official AOCS Method1

A collaborative study was conducted using Spanish peanuts at Oklahoma State University and Virginia peanuts at North Carolina State University regarding the variability in moisture determination using the official AOCS method. The variability among 30 samples was estimated at 5 moisture levels for each of the two peanut types. No difference could be detected between the two types and the data were combined. The standard deviation was linearly related to the mean moisture. Data provided information necessary to compute the number of samples required for a desired precision.

Determination of Low Level Isolated Trans Isomers in Vegetable Oils and Derived Methyl Esters by Differential Infrared Spectrophotometry

A procedure is described for differential infrared spectrophotometric determination of low levels (1–6%) of isolated trans isomers in vegetable oils or derived methyl esters. Triglycerides and methyl esters of known isolated trans content were analyzed by the procedure and results compared with those obtained with the American Oil Chemists’ Society tentative method for isolated trans isomers. Results obtained by the described method are more accurate than those obtained by the AOCS method.

Emulsifiers. III. Periodic Acid Analysis for 1-Monoglycerides

Two collaborative studies were conducted to compare the official AOCS method, Cd 11–57, and a revised Miner procedure. The second study used known materials to obtain accuracy information. Studies showed that the revised Miner procedure is more accurate and more precise at low monoglyceride levels such as those encountered in commercial shortenings. It is recommended that the Miner procedure be adopted as official first action. It is further recommended that the joint AOAC-AOCS methods study of these two procedures be continued so that a single common method can be made official by both societies.