A rapid and accurate method for estimating tomato lycopene content by measuring chromaticity values of fruit puree

Lycopene is the red pigment and a major carotenoid in tomato (Lycopersicon esculentum Mill.) fruit. It is a potent natural antioxidant, and the focus of many tomato genetics and breeding programs. Crop improvement for increased fruit lycopene content requires a rapid and accurate method of lycopene quantification. Among the various available techniques, high-performance liquid chromatography (HPLC) can be accurate, however, it is laborious and requires skilled labor and the use of highly toxic solvents. Similarly, spectrophotometric methods, although easier than HPLC, also require time-consuming extractions and may not be as accurate as HPLC, as they often overestimate fruit lycopene content. Colorimetric estimation of fruit lycopene using chromaticity values has been proposed as an alternative rapid method. Previous studies that examined the utility of this technique, however, were confined to the evaluation of only one or few cultivars and, therefore, lacked broad applicability. The purpose of the present study was to examine the utility of chromaticity values for estimating lycopene and beta-carotene contents in tomato across diverse genetic backgrounds. Measurements of the chromaticity values (L*, a*, b*, C*, h*) were taken on whole fruit and puree of 24 tomato genotypes and were compared with HPLC measurements of fruit lycopene and beta-carotene. Examination of different regression models indicated that a model based on the transformed value a*(4) from puree measurements explained up to 94.5% of the total variation in fruit lycopene content as measured by HPLC. When this model was applied to a second set of fruit harvested at a later date from the same 24 genotypes, it explained more than 90% of the total variation in lycopene, suggesting its reliability. The best estimation for beta-carotene content was obtained by using the b* chromaticity value from whole fruit measurements or the transformed a*(2) value from puree measurements. Neither model, however, could explain more than 55% of the variation in beta-carotene content, suggesting that chromaticity values may not be appropriate for estimating tomato beta-carotene content. The overall results indicated that fruit lycopene content could be measured simply and rather accurately across a wide range of tomato genotypes using chromaticity values taken on fruit puree.