Lycopene (C40H56) is a red carotenoid pigment, which naturally accumulates in flowers, fruits and roots of some vegetable and fruit crops. The unique properties of the lycopene molecule make this pigment one of the most powerful antioxidants available. Tomato (Lycopersicon esculentum Mill.) fruits and processed tomato products are the main sources of lycopene in the human diet. There is a growing amount of experimental data indicating that lycopene intake is associated with decreased risk of many types of degenerative and cardiovascular diseases as well as cancers in humans. In addition, lycopene concentration is associated with improved visual perception of tomato products. Therefore, there is a strong demand to increase the total amount of lycopene in tomato cultivars for either fresh market or processing. The development of cultivars for improved lycopene content is dependent upon the availability of simple yet accurate methodologies to quantify this carotene in tomato fruits and processed tomato products. The main objective of this work was to estimate the degree of correlation between the total lycopene content in tomato fruits measured spectrophotometrically and the chromaticity values (L*, a* and b*) obtained using a tristimulus colorimeter. Colorimetric readings were taken using three sampling strategies: (1) external fruit wall; (2) internal fruit wall and (3) the whole homogenized fruit pulp. For the achromatic component L* (relative darkness or lightness), the obtained R² values were within 0.63 and 0.82, with the whole homogenized fruit pulp providing the highest correlation. For the chromatic component a* (green to red) the correlation R² values ranged from 0.79 to 0.82. For the chromatic component b* (blue to yellow) lower yet significant values were observed (R² between 0.27 and 0.46). However, it was observed that lycopene content was best correlated with the mathematical relationships a*/b* (R² range from 0.88 to 0.90) and (a*/b*)² (R² range from 0.86 to 0.91), with these correlation values being consistently higher when the chromaticity readings were taken in whole homogenized fruit pulp. These results confirmed the feasibility of obtaining precise indirect estimation of lycopene content from chromaticity readings. The methodology described here could be useful for large scale selection of tomato lines with improved levels of lycopene without of high costs and of residue disposal problems associated with the employment of organic solvents in the standard spectrophotometric methods.
Lycopersicon esculentum; colorimeter; pigments; carotenoids; lycopene
