Identification and quantification of free, conjugate and total phenolic compounds in leaves of 20 sweetpotato cultivars by HPLC-DAD and HPLC-ESI-MS/MS

Abstract

The study systematically investigated free, conjugate and total phenolics (phenolic acids and flavonoids) in leaves of 19 Chinese and one American sweetpotato cultivars grown in China. Three extraction/hydrolytic methods (direct extraction and acidic and basic hydrolysis) for sample preparation were employed to obtain different forms of phenolics. Twenty-nine phenolics were separated and identified using HPLC-DAD and HPLC-ESI-MS/MS. Three quercetin glycosides were characterised for the first time from this plant. Contents of the principal phenolics identified were determined by the HPLC-DAD procedure, which was validated in terms of linearity, precision, accuracy and limit of detection and quantification. Moreover, to the best of our knowledge, it is the first to reveal and demonstrate artifacts of esterification during acidic methanolic and ethanolic hydrolysis, and chromatographic behaviours, UV spectra and MS data of 20 hydroxycinnamic acid methyl and ethyl esters were obtained using acidic methanolic and ethanolic hydrolysis.

Keywords: 3,4,5-tri-O-caffeoylquinic acid; 3,4,5-triCQA; 3,4-di-O-caffeoylquinic acid; 3,4-diCQA; 3,5-di-O-caffeoylquinic acid; 3,5-diCQA; 3-CQA; 3-O-caffeoylquinic acid; 4,5-di-O-caffeoylquinic acid; 4,5-diCQA; 4-CQA; 4-O-caffeoylquinic acid; 5-CQA; 5-O-caffeoylquinic acid; Acidic hydrolysis; Basic hydrolysis; CA; CFQA; CQAs; Caffeoylquinic acid methyl and ethyl esters; ChA; ChAs; EDTA–Na(2); FA; FQA; Flavonoids; HBAs; HCAs; Hydroxycinnamic acid methyl and ethyl esters; Phenolic acids; QA; SF; Sweetpotato (Ipomoea batatas L.) leaves; TBHQ; caffeic acid; caffeoyl-feruloylquinic acid; caffeoylquinic acids; chlorogenic acid; chlorogenic acids; ethylenediaminetetraacetic acid disodium; ferulic acid; feruloylquinic acid; hydroxybenzoic acids; hydroxycinnamic acids; p-CoA; p-coumaric acid; quinic acid; sinapic acid; tert-butylhydroquinone.