Lycopene isomers in fresh and processed tomato products: Correlations with instrumental color measurements by digital image analysis and spectroradiometry

Tomatoes (Solanum lycopersicum L.) are food staples that contain high levels of lycopene (LYC), a red carotenoid thought to provide health benefits. Previous studies indicate that instrumental color measurements can be harnessed to estimate carotenoid levels in a rapid and non-destructive fashion, which offers important analytical advantages. In this investigation we have assessed the different LYC isomer contents by HPLC and the color of diverse tomato genotypes and tomato derived-products by SPR and DIA with four main purposes: 1) to compare the levels of LYC isomers in processed vs fresh tomato products, 2) to evaluate the validity of DIA and SPR to ascertain the color of these products, 3) to compare the ability of both instrumental methodologies to discriminate between the two different groups of samples, and 4) to compare the utility of both methodologies for estimating LYC levels. The results indicated that the parameters obtained by SPR and DIA were significantly correlated (p < 0.05) and that the higher regression coefficients were obtained for L*, C*ab and a*. This observation indicates that the DIA is appropriate to evaluate the color of tomato. It was also noticed that, overall, SPR led to better discriminations between samples considering the PCA data (97%).

► The levels of lycopene in fresh and processed tomato products were determined. ► The relative proportions of cis-isomers in both products were very similar. ► The colour parameters obtained by the two methods were significantly correlated. ► Spectroradiometry led to better correlations with the levels of lycopene.