Color analysis
A Labscan XE colorimeter (HunterLab, Inc., Reston, VA.) with the UV filter at nominal position, calibrated with standard white and black plates was used to analyze the color of oil samples. Oil was resented in a sample cup with a black ring and a white disk covered with a black sample cover. Three readings of each sample were recorded. The mean values of the color coordinates L* (lightness - darkness), a* (redness - greenness), and b* (yellowness -blueness) are reported.