Determination of Lycopence in Tomato Products by High Performance Liquid Chromatography and the Correlation with Chromaticity Values

Anvalidated analytical method based on High Performance Liquid Chromatography-Diode Array Detector (HPLC-DAD) was established for the determination of lycopene and its isomers in ketchup. The correlation between the color variables and lycopene content of tomato products from different manufacturers was also discussed. Lycopene was separated by using YMC-carotenoid (C₃₀, 250 mm×4.6 mm, 5 μm) column. Mobile phase contained methanol (A) and methyl tert-butyl ether (B) with flow rate of 1.3 mL/min and was monitored at 472 nm by using DAD. Content of lycopene had a good linear relationship in the concentration range of 10~200 μg/mL (R²=0.9997). The average recoveries ranged from 98.3%~99.6%.The accuracy, expressed in terms of relative standard deviation (RSD), ranged from 2.8% to 4.5%. The method was simple, sensitive, accurate and suitable for the detection of total lycopene in ketchup. The distribution of (all-E)-lycopene and Z-isomers in tomato products was detected and analyzed. The correlation analysis indicated that a*, chroma, a*/b*, hue had remarkable or extremely remarkable correlation with the content of lycopene, the optimal fitting result of regression was R²=0.689.