New Method for the Determination of the Induction Period of Walnut Oil by Fourier Transform Infrared Spectroscopy

A new method for the determination of the induction period (IP) of walnut oil through polyethylene-film-based Fourier transform infrared (PE-FTIR) spectroscopy was developed. The IP value was used to represent the oxidation stability of walnut oil. The characteristic infrared spectrum peaks at 3008, 1654, 914, and 723 cm(-1) changed significantly as the IP value decreased. The prediction model was established on the basis of these changes. The optimal partial least squares model was established under the following conditions: constant, original spectra, no smoothing, and wavelength range of 1640-440 cm(-1). The calibration set of the model provided a coefficient of determination (R-2) of 0.9847 and a root mean error of calibration of 3.38. The R-2 and the root mean square error of prediction for the validation set were 0.9878 and 2.32, respectively, and were 0.9948 and 3.61 for the blind sample validation set, respectively. In precision evaluation, the standard deviation and coefficient of variation of the predicted values were 4.13 and 4.19%, respectively. The present results indicated that the polyethylene-FTIR method for analyzing the IP value of walnut oil was simple and rapid and could be used as a highly effective alternative to the traditional determination method.