Phytochemical screening and assessment of health-related bioactivities of phenolic compounds from yacon [Smallanthus sonchifolius (Poepp. and Endl.) H. Robinson] leaves and tubers

Yacon [Smallanthus sonchifollius (Poeppig and Endlicher) H. Robinson], a tuber crop originally cultivated in the Andean region of South America, has been used as food and in traditional medicine by the native inhabitants for centuries. This study determined the nutritional value of yacon grown in Nueva Ecija [Philippines], characterized the phenolic constituents and evaluated their health-related bioactivities. By proximate analysis, a 100-gram sample of freeze-dried yacon tuber was found to contain low levels to protien (2.43 g), moderate level of fiber (4.47 g) and high level of carbohydrates (73.8 g). A 100 g sample of dried yacon leaves contained high level of protein (15.24 g) and fiber (5.67 g), and moderate level of lipids (2.81 g). Potassium comprised more than 50% of the total mineral content of yacon leaves and tuber, as determined by ICP-OES. Phytochemical screening showed the presence of phenolics, alkaloids, sesquiterpene lactones, terpenoids and triterpenoids; and absence of cyanogenic glysides, saponins and glucosinolates in yacon leaves and tubers. The total phenolic contents of the tuber and leaf extracts, as estimated by the Folin-Ciocalteu method (in terms of mg GAE per 100 g sample and mg QE per 100 g sample) were : tuber methanol extract (164.2 ± 16.9 and 167.5 +- 15.0), leaf decoction extract (3,489.4 +- 129.9 and 3,484.7 +- 142.1) and leaf methanol extract (529.2+-52.4 and 214.8 +- 46.1). Descending two-dimensional paper chromatography, TLC and RP-HPLC analyses of the phenolic extracts and their products from acid- and base-hydrolysis showed that caffeic and its esters and derivatives were the major phenolic components. Quantification by RP-HPLC showed high levels (in terms of mg per 100 g sample) of a caffeic acid ester in the tuber extract (155.32 ± 0.67) and leaf decoction (186.72 ± 4.55), caffeic acid in the based-hydrolyzed leaf decoction (395.3 +- 0.7) and ferulic acid in the acid-hydrolyzed leaf decoction (43.32 +- 7.00). Results from chromatographic analyses corroborated by the isolation and identification of the following compounds by silica gel open column chromatography. Sup 1 H-NMR spectroscopy and melting point determination; caffeic acid from leaf decoction based-hyrolysed extract, and ferulic acid from leaf decoction acid-hydrolyzed extract. The phenolic extracts were found to have significant DPPH radical scavenging activity. Furthermore, the phenolic extracts exhibited significant anti-lipoperoxidative activity on rat liver microsomes comparable to a commercial supplement containing silymarin extract, which is recommended for hepatoprotection. Using duck embryo CAM vascular irritation assay, the phenolic extracts were found to possess an anti-inflammatory activity comparable to hydrocortisome.