Differences in the carotenoid content of ketchups and gazpachos through HPLC/ESI(Li+)‐MS/MS correlated with their antioxidant capacity

Abstract

Carotenoids are important antioxidant compounds in the human diet. Owing to their constrained polyene structure, carotenoids can exist in cis and trans isomeric forms that can be difficult to differentiate in natural samples. In ketchups and gazpachos, all-trans isomeric forms are predominant. However, during thermal processing, cis isomers are formed. Therefore the determination of carotenoid isomers is required for the assessment of the nutritional value of foods. The main carotenoid found in ketchups was trans-lycopene, whereas in gazpachos a higher contribution to the total carotenoid content was made by other carotenoids such as 5-, 9- and 13-cis-lycopene, lutein, β-carotene and α-carotene. Ketchups exhibited the highest lipophilic antioxidant content owing to their higher content of trans-lycopene, the main carotenoid in tomatoes. Direct analysis of carotenoids by electrospray ionisation mass spectrometry (ESI-MS) often produces poor results requiring offline time- and sample-consuming derivatisation techniques. Therefore in this work a simple ESI-MS approach is described for the direct analysis of carotenoids in ketchups and gazpachos using the post-column addition of lithium chloride to promote the cationisation of carotenoids. To the best of the authors' knowledge, this paper presents for the first time the identification of 5-, 9- and 13-cis-lycopene in ketchups and gazpachos.