Reversed phase HPLC analysis of alpha- and beta-carotene from selected raw and cooked vegetables

Traditional AOAC colorimetric procedures for carotenoid analysis are known to lack specificity and accuracy. Newer HPLC methods provide the investigator with a more precise tool for carotenoid quantification in foods and tissues. In the present studies, reverse phase HPLC was utilized to evaluate the alpha- and beta-carotene content in raw and cooked leaves of lettuce, spinach and winged bean as well as in the carrot root. The vegetables were boiled or steamed and the true retention of alpha- and beta-carotene in the cooked products was determined. Boiling for 30 minutes resulted in a 53 and 40% loss of beta-carotene from lettuce and carrots, respectively. Full retention or even an increase in beta-carotene content in boiled winged bean leaves and spinach was noted. Steaming resulted in very good retention of alpha- and beta-carotene in all vegetables (83-139% retention). Thus, although cooking procedures (especially boiling) may result in oxidative loss of carotenoids in some vegetables, heat treatment increases the chemical extractability of alpha- and beta-carotene in others. The presence of carotenoproteins in some vegetables may affect the heat stability of extractability of alpha- and beta-carotene.