Identification of 4-O-5‘-Coupled Diferulic Acid from Insoluble Cereal Fiber

Abstract

The extracts of saponified cereal fibers of whole grains of corn (Zea mays cv. microsperma KOERN.), wheat (Triticum aestivum L.), spelt (Triticum spelta L.), and rice (Oryza sativa L.) were investigated for dehydrodimers of ferulic acid using gas−liquid chromatography (GLC) with mass spectrometric detection (GLC−MS) and flame ionization detection (GLC−FID). In addition to the 8,5‘-, 8,8‘-, 5,5‘-, and 8-O-4‘-coupled diferulic acids previously identified from other plant materials the 4-O-5‘-coupled diferulic acid (E)-3-[4-[(E)-2-carboxyvinyl]-2-methoxyphenoxy]-4-hydroxy-5-methoxycinnamic acid (4-O-5‘-DFA) was identified in all fibers investigated. This new diferulate was authenticated by comparison of its mass spectrum and its relative GLC retention time with those of the synthesized compound. Semiquantitative determination of 4-O-5‘-DFA showed that it is present at 8−30 μg/g, approximately 70−100 times lower concentrations than the sum of 8,5‘-coupled diferulic acids, the major diferulic acids in the investigated fibers. Keywords: Ferulic acid; diferulic acid; diferulate; insoluble fiber; cereals; cell wall cross-linking; GC−MS