Effects of Chinese domestic cooking methods on the carotenoid composition of vegetables in Taiwan

Abstract

Carotenoids, lutein, zeaxanthin, and β-carotene, common in many vegetables, have been shown to be important in visual health-promoting. However, cooking practice has a great impact on these bioactive compounds. The objective of this work was to evaluate the effect of three common Chinese domestic cooking methods including boiling, stir-frying, and deep-frying on the composition of lutein, zeaxanthin, β-carotene and their trans/cis (E/Z) isomers of vegetables. Among the 25 fresh vegetables commonly consumed in Taiwan, it was found that cilantro, Thai basil leaves, sweet potato leaves, and choy sum contained the 1st–4th highest amount of total carotenoids content (TCC), respectively. Boiling preserved the majority of carotenoids, whereas stir-frying and deep-frying significantly decreased TCC and (all-E)-forms of carotenoids. In addition, (all-E) – and (13Z)-/(13′Z)-carotenoids exhibited similar trends during boiling, since the boiling time required to reach maximum concentration for (all-E)-carotenoids was almost the same as that for (13Z) – plus (13′Z)-isomers. An overall increase of (9Z)/(9′Z)-carotenoid isomers was observed in all boiled vegetables, probably because of E/Z isomerization, which could partially result in the formation of more bioactive compounds such as (9Z)-β-carotene. Boiling may be the preferred practice of domestic cooking methods to preserve carotenoids in vegetables.