The fluorescence emission spectra of walnut oil, peanut oil, soybean
oil and palm oil are shown in Fig. 3. They exhibited some differences
in the peak position and peak intensity, particularly in the
emission wavelength region of 400–500 nm. The peak position of
walnut oil was at 473 nm, whereas peanut oil, soybean oil and
palm oil were at 428, 439, and 434 nm, respectively. The fluorescence
intensity of walnut oil was the lowest. The strong bands
between 400 and 500 nm in emission have been attributed to a
range of fatty acid oxidation products and tocopherols, and the
low intensity bands between 600 and 700 nm in emission were