VNIISSOK, Odintsovo Region, Moscow Province, 143080 Russia, e-mail vniissok@mail.ru, anirr@bk.ru; 64/13, Volodymyrska Str., Kyiv, 01601 Ukraine, e-mail korenevochka@mail.ru, lmishchenko@ukr.net; Ukraine, e-mail dannaval@mail.ru A b s t r a c t Antioxidants regulate functional activity and reduce the risk of development of diseases. <...> Deficiency of antioxidants leads to sharp decrease in resistance to adverse factors. <...> The vegetable food is the main and most available source of antioxidants for the human. <...> Yudinka originated by All-Russian Research Institute of Vegetable Breeding and Seed Production), was successfully introduced in Ukraine. <...> The content of the biologically active substances (BAS) in plants is known to be influenced by transfer from the places of natural growth in other climatic conditions, and by biotic factors, too. <...> Despite it, only a few papers are devoted to studying of the content of phenols, oligofructans and other BAS in the yacon depending on cultivation and storage conditions, and the data on an influence of pathogens on the BAS in the yacon are absent. <...> Therefore our aim was to determine the level of the main BAS (phenolic compounds and fructosans) in yacon of the Ukrainian introduction (in leaves and root tubers), and also to estimate the influence of biotic factors. <...> The chromatography analysis of ethanol extracts from yacon leaves and root tubers showed the phenolic compounds among which the derivatives of hydroxycinnamic acids (HCA) prevailed. <...> Using the high-efficiency liquid chromatography, it was shown that in the ethanol extract of dry yacon root tubers the derivatives of HCA are mainly presented by a not identified peak (X1) with keeping time of 11.45 min, and also chlorogenic and caffeic acids were found. <...> Main phenolic component of the fresh root tuber ethanol extracts was a substance with keeping time of 12.21 min (X2) which was absent in the dry root tubers and also was a derivative of caffeic acid. <...> The content of chlorogenic and caffeic acids in fresh yacon root tubers was higher compared to dry ones, thus there are labile HCA derivatives changed when drying. <...> We also studied other ( species , , , , Cav.), and, unlike yaсon, found one dominant peak of caffeic acid derivatives. <...> It was cichoric acid in coneflower and dandelion leaves, chlorogenic <...>