Ferulic acid dehydrodimers as structural elements in cereal dietary fibre

Abstract

Investigations on insoluble dietary fibre (IDF) of wheat, rye, barley, oat, maize, rice and millet led to the identification of several new dehydrodimers of ferulic acid (DFA). These compounds arise from 8–8′, 8–5′, 8–O–4′ and 5–5′ coupling. Esterified phenolics were set free by mild alkali hydrolysis, total amounts of phenolics (ester- plus etherified) were determined by alkali hydrolysis under pressure. Phenolic acids were analysed by gas chromatography – mass spectrometry (GC-MS) as their trimethylsilyl (TMS) derivatives and by high performance liquid chromatography – diode array detection (HPLC-DAD). In esterified form 8–8′aryl DFA and 5–5′ DFA dominate in most cereal IDF with, together, 45–60% of the DFA sum. More than 60% of total bound DFA are involved in ether linkages. Highest amounts of esterified as well as etherified DFA are estimated in millet, followed by maize. DFA contents of wheat, rye and barley are about two- to threefold lower than in millet but about twofold higher than in oat or rice.