Key words Carotenoids
Electron spin resonance
Springer Online Journal Archives 1860-2000
Process Engineering, Biotechnology, Nutrition Technology
Abstract The influence of eight commonly occurring carotenoids on (1) the production of spin adducts, (2) the hyperfine splitting constants a H and a N of the spin adduct electron spin resonance (ESR) spectra, and (3) the production of the oxidized N-tert-butyl-α-phenylnitrone (PBN) derivative N-benzoyl-N-tert-butylnitroxide (PBNOx) was investigated in ESR spin-trapping experiments, in which radicals were thermally generated from 2,2′-azobis(2,4-dimethylvalero nitrile) (AMVN) and trapped by PBN. In the polar solvent acetone under air, all carotenoids except β-carotene were shown to diminish the number of spin adducts formed by about 20%. A prooxidative effect of β-carotene was even demonstrated at a higher concentration. In the less polar solvent toluene under air, most carotenoids lowered the amount of spin adducts, but effects were not as large as in acetone, and differences were found between (1) the more effective carotenoids with two cyclohexene rings conjugated to the polyene backbone (and lycopene), and (2) carotenoids with zero or one conjugated cyclohexene ring. The formation of PBNOx in toluene, which was essentially due to breakdown of peroxyl spin adducts, was significantly inhibited by astaxanthin, canthaxanthin and lycopene. Throughout, only alkoxyl radical adducts of PBN were observed. However, a significant difference was found between the a H values of zeaxanthin and the carbonyl carotenoid astaxanthin, indicating structural differences of the spin adducts.
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