EFFECT OF WAVELENGTH ON LIGHT-INDUCED QUALITY DETERIORATION OF EDIBLE OILS AND FATS

Rapeseed, corn, soybean and coconut oils and milk fat were subjected to fluorescent light irradiation. Effect of different wavelengths on the relative oxidation rate was studied using several sharp-cut filters transmitting exactly defined wavelength (350-370 nm). The oxidation rate was followed by the peroxide values. A distinct decrease in the oxidation rate with increasing wavelength was observed in all of the oils and fats. To study the cause of this behavior, transmission curves for these samples were determined. Short wavelengths were absorbed; long wavelength light was barely absorbed. The photo-oxidative effect per unit of radiant energy intensity in relation to wavelength varied and was characteristic of each oil or fat. The oxidation rate as determined in the darkness was greater in photo-bleached milk fat than in any other oil. Susceptibility of these oils or fats to photo-oxidation did not depend on the degree of unsaturation alone. After extinguishing the light the oxidation rate dropped to a very low level.