Development and evaluation of an HPLC method for the analysis of carotenoids in foods, and the measurement of the carotenoid content of vegetables and fruits commonly consumed in the UK

Abstract

This study further examines the factors which affect the chromatographic response of carotenoids and contribute to analytical variation and inaccuracies in their quantitative determination. A method for the analysis of carotenoids in vegetables and fruits is described and data are presented for the carotenoid content of vegetables and fruits commonly consumed in the UK. The addition of a solvent modifier (triethylamine) to the mobile phase was shown to improve the recovery of carotenoids from the column from around 60% to over 90%. The linearity and reproducibility of the chromatographic response was investigated and the robustness and reproducibility of the method was measured using a reference vegetable material developed in the laboratory. Short and longer term reproducibility showed an average CV of around 8% for all carotenoids. Analysis showed that good sources (>1000 μg/100 g) of lutein were broccoli, butterhead lettuce, parsley, peas, peppers, spinach and watercress; of lycopene: tomatoes and tomato products; and of β-carotene: broccoli, carrots, greens, butterhead lettuce, mixed vegetables, parsley, spinach and watercress. There was little or no loss of carotenoids on cooking, green vegetables showed an average increase in lutein levels of 24% and in β-carotene levels of 38%. This study and previous studies in our laboratory have demonstrated that a number of factors affect the validity of the ‘peak response’ and are likely to contribute to within and between laboratory variation. It is suggested that the development and use of standard reference materials would significantly improve the quality of data.