10th Symposium on the Flora of Southeastern Serbia and ...

10 th <strong>Symposium</strong> on the Flora of Southeastern Serbia and Neighbouring regions,Vlasina 17 to 20 June 2010transducers, expressing notable anti-cancer behaviour. The updated studiesconnected flavonoids antioxidant activity with presence (or absence) of OH-group atC-ring 3-position, in combination with catechol B-ring structures. The importance ofthis position (wherever exists, like in flavonols – represented by quercetin) may beestimated – among other ways – by comparing stabilities of quercetin and rutin(flavon representative – not having 3-OH group) toward an extternally indicedstress, like UV-irradiation. The plant answer on the increased presence of highlyenergeticUV-B fraction in sunlight spectrum is, among others, an increasedsynthesis of UV-B absorbing pigments, mostly flavonoids (flavonoids screeningaffect). The last fact was exploited in this work. Their chemical structures permitthem to be excellent UV-absorbers which enables them to be (a) efficient preventiveantioxidants, because they reduce initiation, e.g. decrease production of free radicals(which is one of the main consequences of continuos UV-irradiation). But, in thesame time they are (b) very effective chain-breaking antioxidants, acting asscavengers of the created radical species. Both (a) and (b) are especially importantfor inhibition of lipid peroxidation (LP) process. There is undoubtfull correlationbetween stability of flavonoids toward UV-irradiation and degree of LP suppression(case (a)). This contribution deals with studies of two selected flavonoids, quercetinand rutin, subjected to continous, prolonged irradiation from three UV-sub-ranges:UV-A, 320-400 nm; UV-B, 290-320 nm; UV-C, 200-280 nm), in solution, in thepresence or in the absence of „protective target“ soy bean lecithin. The change of theflavonoids stability was related to degree of the (UV-) induced lecithin peroxidation,under the same irradiation regime. The 3-OH group was found to play the crucialrole concerning the flavonoids photostability: the flavonoids with 3-OH in thestructure are less resistent toward UV-irradiation – in this case quercetin undergoesto faster destruction (bleaching) than rutin, and the bleaching is energeticallydependent(following UV-C > UV-B > UV-A order). TBA-MDA test used to followchanges in the two flavonoids antioxidant activities – toward lecithin as theprotective target – also expressed the same UV-energy-dependent order as theoutcome. It was also found that rutin antioxidant activity is more influenced by UVeffectthan quercetin’s.87