Riichiro Usuki

Prooxident activities of chlorophylls and their decomposition products on the photooxidation of methyl linoleate

Although chlorophylls in oils affect oxidative stabilities, little has been known about the prooxidant activity of the chlorophylls or their decomposition products. To evaluate the prooxidant activities of chlorophyll derivatives, chlorophyll (CHL) A and B, pheophytin (PHY) A and B and pheophorbide (PHO) A and B were added to methyl linoleate (ML). The sample oils were then subjected to photooxidation at O C and the peroxide value and absorbance at 234 nm were measured. Chlorophylls catalyzed oxidation of methyl linoleate at concentrations greater than 2.2×10−9mol/g ML, and CHL B showed a stronger prooxidant activity, ca. twice that of CHL A under the same light intensity. PHY and PHO exhibited stronger prooxidant activities than CHL, the prooxidant activity of PHO being the strongest among them. Moreover, photosensitive activity was found in PHY as well as in CHL. These results suggest that particular attention should be paid to the decomposition products of CHL that affect the quality of vegetable oils.

Residual amounts of chlorophylls and pheophytins in refined edible oils

The quantities of chlorophyll (CHL) A and B, and pheophytin (PHY) A and B in 10 kinds of refined edible oils were estimated by the fluorometric method. The results revealed that CHL and PHY were present in commercial edible oils. PHY A showed the highest content at ca. 67% in total pigments. Compositional ratios of CHL and PHY were similar in different kinds of plant oils. Through the analysis of rapessed oils at every refining step, we determined that PHY is not formed during oil refining. In the autoxidation of soybean oils to which various amounts of CHL mixtures had been added, the peroxide value of tested oils increased in proportion to the total chlorophyll content. In addition, the compositional changes of the 4 components during autoxidation were investigated.