Antioxidant and antimicrobial activity of linseed lignans and phenolic acids

Abstract

In this study, we present antioxidant and antimicrobial activity of isolated lignans freed of other bioactive compounds in comparison with dominant phenolic acids. The combinations of screw pressing, solvent extractions, acid-catalysed hydrolysis and flash chromatography were used to describe and isolate linseed phenolic compounds. Secoisolariciresinol, ferulic, p-coumaric and caffeic acids were the most abundant ones while salicylic, gentisic, dihydro-p-coumaric, phenylacetic, vanillic, p-hydroxybenzoic and β-resorcylic acids were the minor secondary metabolites. Anhydrosecoisolariciresinol (ANHSECO) and levulinic acid were an artefacts formed during exhaustive hydrolysis. The effective concentration (EC50), antiradical power (1/EC50), stoichiometry (2·EC50) values and second order rate constants k 2 were determined to classify antioxidants according to reaction kinetics as slow (p-coumaric acid derivatives), medium (ferulic acid derivatives, secoisolariciresinol and ANHSECO; k 2 ranges from 1.85 to 2.29 μmol−1 dm3 s−1) and fast (caffeic acid derivatives; k 2 = 6.91 μmol−1 dm3 s−1) ones. Rancimat method was simulating lipid peroxidation and its inhibition. Linseed lignans and phenolic acids could be classified according to protection of unsaturated triacylglycerols in the following order: p-coumaric acid < ANHSECO < methyl p-coumarate < ferulic acid < secoisolariciresinol < methyl ferulate < crude extract < caffeic acid < methyl caffeate. The mechanism and the formation of secoisolariciresinol oxidation products were discovered by mass spectrometry. The effect of crude linseed extract, ANHSECO, caffeic, ferulic and p-coumaric acid on the growth of Gram-negative bacteria, Gram-positive bacteria, yeasts and moulds was also determined.