Phenolic compounds and fructosans in yacon ( Polymnia sonchifolia Poepp. & Endl.) cultivar introduced in Ukraine, and in other Asteraceae plants as influenced by growth conditions, viral and phytophage injury

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. Yacon ( Polymnia sonchifolia Poepp. & Endl. syn. Smallanthus sonchifolia ), a new perspective plant (сv. 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 Asteraceae species ( Echinacea purpurea, Arctium lappa, Helianthus tuberosus, Taraxacum officinale, Dahlia Cav.), and, unlike yaсon, found one dominant peak of caffeic acid derivatives. It was cichoric acid in coneflower and dandelion leaves, chlorogenic acid in girasol leaves, and not identified substance (X3) coinciding in keeping time with cichoric acid in burdock leaves. In yacon leaves the accumulation of HCA derivatives was higher. Majority (not less than 18) peaks on the chromatogram had a HCA specific UF-spectrum. Three components with keeping time of 7.1-7.6 min could be identified as flavonols with regard to UF-spectra. According to direct spectrophotometry of ethanol extracts, the total amount of hydroxycinnamic acids varied from 2.8 to 4.3 % (as chlorogenic acid per absolutely dry weight) depending on position of leaves on the plant. In root tubers the fructosans level changed from 36 to 45 % depending on the region of cultivation and weather conditions. A comparative assay showed that in the root tubers of yacon multiplied by cutting the fructosans level was 4.98 % higher than if the cutting was not used. Note, the fructosans level in the yacon root tubers was higher compared to girasol and dahlias tubers which are known as their effective sources with 6.2 % and 3.03 % level, respectively. A decrease in the content of main BAS in root tubers of the yacon plants influenced by biotic agents such as viruses and phytophages was also found. Particularly, in infected and damaged yacon plants the low-molecular fructosans, the sum of fructose and total fructosans, and the inulin accumulation were 8.9 %, 13.9 % and 5 % lower, respectively. Thus, the data obtained by us showed that yacon is the perspective source of fructosans and antioxidants which can be used in manufacturing bioactive preparations.