Thermal processing may result in losses of all-trans-carotenes and the formation of cis isomers. In fact, a reduction in the percentage of all-trans-b-carotene with the concomitant increase of 13-cis and 9-cis isomers has been observed during processing . Losses of all-trans-a- and all-trans-b-carotene were greater during atmospheric frying, probably as a result of their isomerisation at elevated temperatures. In fact, formation of 13-cis-b-carotene was observed in carrot crisps fried at 160 C and 180 C, representing 12.5 ± 1.1% and 28.6 ± 1.4% of total carotenes, respectively. noted that cis isomers could account for as much as 29% of total b-carotene content in processed sweet potatoes. Trans–cis isomerisation affects pro-vitamin A activity and the antioxidant capacity of carotenoids.