| Abstract
| - Isomerization of carotenoids, which is often encountered in food processing under the influence oftemperature and light, may play a role in the observed protective effects of this group of secondaryplant products. Investigation of in vitro antioxidant activity of prominent carotenoid geometrical isomerswas undertaken in light of recent reports illustrating a large percentage of carotenoid (Z)-isomers inbiological fluids and tissues. α-Carotene, β-carotene, lycopene, and zeaxanthin were isolated fromfoods or supplements and subsequently photoisomerized with iodine as a catalyst. Major Z-isomersof each carotenoid were fractionated by semipreparative C30 HPLC. In vitro antioxidant activity of allisomers collected was measured photometrically using the Trolox equivalent antioxidant capacity(TEAC) assay. TEAC values of 17 geometrical isomers investigated ranged from 0.5 to 3.1 mmol/L.Three unidentified (Z)-isomers of lycopene showed the highest antioxidant activity, being significantlyhigher than the result for (all-E)-lycopene, which had approximately two times the activity of (all-E)-β-carotene. On the other hand, (9Z)-zeaxanthin had a more than 80% lower TEAC value comparedto that of (all-E)-lycopene. These results allow for the in vivo relevance of (Z)-isomers of carotenoidsto be considered. Keywords: Trolox equivalent antioxidant capacity; α-carotene; β-carotene; lycopene; zeaxanthin;geometrical isomers
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