Year: 1999
Type: dissertation
Abstract: This thesis dealed with antioxidant/pro-oxidant action of carotenoids in in vitro lipid systems.The review of literature described the antioxidant/pro-oxidant chemistry of carotenoids and summarized the available data on the antioxidant/prooxidant action of carotenoids in different lipid systems.The experimental part evaluated the effects of carotenoids and carotenoid-tocopherol interaction on lipid oxidation based on free radical scavenger properties by electron spin resonance (ESR) study and the formation and decomposition of hydroperoxides.In ESR spin-trapping experiments, radicals were thermally generated from (2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN) and trapped by N-tert-butyl-αphenylnitrone (PBN).In acetone, all carotenoids (0.17 mM) except β-carotene diminished the formation of the amount of spin adducts.β-Carotene was a prooxidant at higher concentration (0.90 mM).In toluene, all carotenoids except lutein, bixin and a combination of lutein and β-carotene diminsihed the amount of spin adducts.The differences in free radical scavenging between eight carotenoids including β-carotene, astaxanthin, canthaxanthin, zeaxanthin, lutein, cryptoxanthin, lycopene and bixin were small.The effects of carotenoids on the formation of hydroperoxides was examined in three different lipid models in vitro: triacylglycerol fraction of rapeseed oil (RSO TAGS), emulsified RSO TAGS and methyl linoleate.The decomposition of hydroperoxides was examined in emulsified RSO TAGS.Based on promotion of hydroperoxide formation, β-carotene (20 µg/g), lutein (5-40 µg/g) and lycopene (20 µg/g) were pro-oxidants in autoxidized RSO TAGS.Based on both formation and decomposition of hydroperoxides, β-carotene (0.45-20 µg/g) was a pro-oxidant in emulsified RSO TAGS.In methyl linoleate, both β-carotene (5-200 µg/g) and its oxidative breakdown product, retinal (7-360 µg/g), promoted the formation of hydroperoxides.The pro-oxidant effect was stronger with higher concentrations of the carotenoid.This thesis raised the question of the effect of carotenoid breakdown products on pro-oxidant role of carotenoids as demonstrated with retinal.The loss of yellow colour indicates the pro-oxidant action of carotenoids in lipids.On the other hand, even a minor amount of tocopherol protected carotenoids from destruction and thus from pro-oxidant effect.In RSO TAGS and emulsified RSO TAGS, a combination of carotenoid and tocopherol at certain proportion was a more efficient antioxidant than tocopherol alone.In conclusion, the present results demonstrated that carotenoids are in vitro prooxidants in lipid environment and may act as free radical scavenging antioxidants in chemical solutions.
Source: Työväentutkimus Vuosikirja
Author: Katri Haila
Language: English
Subfield: Biochemistry (medical)
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W140262561