Objective measurement of red grapefruit juice color

The color properties (CIE L*a*b*, hue, and chroma) of 90 red grapefruit juices were studied by tristimulus reflectance measurement for two growing seasons. Juices were prepared from six red grapefruit cultivars including Ruby Red, Rio Red, Star Ruby, Ray Ruby, Flame, and Marsh Red grown in Florida. Very wide varietal and seasonal variations on juice color were observed, and most notably, CIE a* values varied widely from -1.41 to 9.06 (CV = 82.6%). Lycopene is the major colored pigment in red cultivars with lesser amounts of beta-carotene as determined by HPLC on a carotenoid C-30 column with gradient elution using MeOH and MTBE. The highest correlation coefficients (r = 0.963) found between CIE a* values and lycopene contents in juices from all cultivars combined suggest the possibility that the CIE a* value would be a good indicator for pigmentation in red grapefruit juice.