Content of carotenoids in commonly consumed Asian vegetables and stability and extractability during frying

In order to investigate the variation in β-carotene and vitamin A in commonly consumed vegetables in Asia, different leafy vegetables were analyzed. The mean β-carotene content varied between 16 and 6630 μg/100 g fresh weight (FW) with the highest content in drumstick leaves and the lowest content in common cabbage and Garland chrysanthemum leaves. In six tuber and fruit vegetables, the mean β-carotene content varied between 311 and 15,400 μg/100 g FW with the highest content in a chili pepper variety. Vitamin A activity varied significantly between the investigated vegetables (1–1280 μg retinol activity equivalents (RAE)/100 g FW). The retention of β-carotene and formation of cis-isomers were investigated in selected vegetables during stir-frying. Retentions of all-trans-β  -carotene varied between 73% and 98% in sweet bell pepper, sweet potato and tomato that were fried for 12–3min. In sweet potato, 13-cis-β-carotene was the major cis-isomer of β-carotene, while only minor amounts of 15-cis- and 9-cis-β-carotene were formed. The total amount of cis-isomers of β-carotene formed during frying depended on the frying time and the size with the highest amount in cubes, that were fried for 3 min (1070 μg 13-cis-β-carotene/100 g FW). In leafy vegetables, only 13-cis-β-carotene was detected during frying. Extraction of β-carotene into the frying oil was only observed in low amounts after 3 min frying of sweet potato shreds.