Changes in the concentration of phenolic compounds during growing, storing, and processing of yacon

Abstract

Changes in the concentration of major phenolic compounds that occurred during growing, storing and processing of yacon (Smallanthus sonchifolius) were investigated from the viewpoint of effective usage of the functional ingredients in yacon. Major phenolic compounds, chlorogenic acid (1), 3,5-di-O- caffeoylquinic acid (2), 2,4- or 3,5-di-O-caffeoylaltraric acid (3), 2,5-di-O-caffeoylaltraric acid (4), 2,3,5- or 2,4,5-tri-O-caffe-oylaltraric acid (5), 4-O-caffeoyl-2,7-anhydro-D-glycero-β-D-galacto-oct-2-ulopyranosonic acid (6), and 4,5-di-Ocaffeoyl-2,7-anhydro-D-glycero-β-D-galacto-oct-2- ulopyranosonic acid (7) had high DPPH radical scavenging activities. 4,5-Di-O-caffeoyl-2,7-anhydro-D-glycero-β-D-galacto-oct-2-ulopyranosonic acid methyl ester (8) occurred in the leaf and stem and was elucidated by MS and NMR spectroscopy. The concentration of compounds 1-8 peaked in the stem during the early stages of yacon growth. In the leaf, tuberous root, and tuberous stem, it peaked in the latter stage of growth. However it did not change during storage of the tuberous root, The phenolic compounds in yacon leaf and tuberous root were retained well by drying with hot air at 40-60°C, but most of them were lost at 80-100°C. About half of the phenolic compounds in yacon noodle prepared with the heat-treated yacon leaf powder were retained, but about 80% of phenolic compounds were lost in the noodle prepared by yacon leaf powder without heat treatment. The reduction in the concentration of phenolic compounds during processing yacon was assumed to be due to polyphenol oxidase.