Phenolic Compounds in Flaxseed Chromatographic and Spectroscopic Analyses of Glucosidic Conjugates

Johnsson, P. 2004. Phenolic compounds in flaxseed: Chromatographic and spectroscopic analyses of glucosidic conjugates. Licentiate thesis. ISSN 1101-5411, ISBN 91-576-6630-x The dietary lignan secoisolariciresinol diglucoside (SDG), present in high concentrations in flaxseed, and its metabolites enterolactone and enterodiol are thought to decrease the risk of hormone dependent cancers, cardiovascular disease and other “welfare” diseases. Flaxseed also contains other biologically active phenolic compounds, such as phenolic acids. The understanding of the nature of these compounds is crucial for their possible exploitation in drugs and functional foods. Until the mid 1990’s, the number of methods available for analysis of lignans and other compounds in flaxseed was limited and were divergent in terms of yields. Moreover, the structure of a “flaxseed polymer” to which these phenolic compounds are bound was not known. Thus, the aim of the work presented in this thesis was to develop a quantitative method for analysis of SDG in flaxseed and to unravel the structure of the “polymer”. A high performance liquid chromatography (HPLC) method for quantification of SDG in a base hydrolysed dioxane/ethanol flaxseed extract was developed. The method was applied to study the SDG content in 14 Swedish and 15 Danish flaxseed cultivars. The SDG content in defatted flour from the cultivars varied between 11.7 and 24.1 mg/g (6.1 – 13.3 mg/g in dried seeds). Two chromatographic peaks eluting before SDG in the developed HPLC system were identified as 4-O-β-D-glucopyranosyl-p-coumaric acid and 4-O-β-Dglucopyranosyl-ferulic acid by liquid chromatography-mass spectrometry and nuclear magnetic resonance (NMR) analyses. Moreover, by the use of different NMR techniques, a strait chain oligomeric structure with an average composition of five SDG residues interlinked with four 3-hydroxy-3-methyl glutaric acid residues was assigned to the “polymer”.