Modified ABTS cation radical decolorization assay and EPR technique were applied to screen the antioxidant activity of three flavonoids with different polarity: 7-O-β-[2-O-feruloyl-β-glucuronopyranosyl (1→2) glucuronopyranoside] (tricine), 4'-methoxy-5,7-dihydroxyflavone 6-C-β-glucopyranoside (isocytisoside) and I 3' II 8 biapigenine (amentoflavone), with nonpolar all-trans β-carotene used as standard carotenoid molecule. The ABTS [2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid] cation radical decolorization assay was modified as follows: (1) measurements extended up to 8 days after preparation, (2) method adapted for flavonoids with different polarity and β-carotene, (3) concentrations in the 0.01-10 μM range of both trolox and antioxidants in order to use the same experimental conditions for both this technique and EPR measurement.

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The clear vibrational structure of fluorescence spectrum of β-carotene in the solvent is reported for the first time at room temperature. This finding is in good agreement with recently discovered covalent 3 1 A g -new carotenoid state. The fluorescence yield of β-carotene in ionic liquid (1-methyl-3-octyloxymethylimidazolium tetrafluoroborate) is around hundred times higher than in standard solvent n-hexane. The all-trans and 15-cis β-carotene fluorescence yields in ionic liquid are 1.96±0.03 and 2.53±0.03 %, respectively. The ionic liquid is a very useful tool for modelling photosynthetic system in situ. We present the electronic absorption data of β-carotene in ionic liquids (so called neoteric solvents) with special interest in the absorption changes as a function of temperature in the range 0-90 o C (273-363 K). Ionic liquids are also very good medium for temperature study, because they are not changing up to several hundred o C and also not evaporating during heating. The relationship between spectral characteristics of β-carotene in new generation solvents with increasing and decreasing temperature is evaluated. The energy value of the ionic state 1 1 B u + of synthetic β-carotene in ionic liquids exhibits a linear and temperature reversible dependence on temperature up to 30 o C (303 K) and up to 40 o C (313 K) for 15-cis and all-trans β-carotenes, respectively. This is valid for both 0-0 and 0-1 transitions.