Phenolic acid composition and antioxidant potential of insoluble and soluble dietary fibre extracts derived from select whole-grain cereals

The consumption of whole-grain cereals (WG) has been revealed to be associated with the reduced risk of developing chronic diseases. Cereal dietary fibre (DF), as an abundant source of plant cell wall bound hydroxycinnamic acids, can be considered as an important contributor to the health benefit of WG consumption. In the present study, major phenolic acids in WG and DF alkaline extracts were analysed by reversed phase high performance liquid chromatography (HPLC) coupled with photodiode array detection (PDA) and quadrupole-time of flight mass spectrometry (Q-TOF MS). Eight monomeric phenolic acids (protocatechuic, vanillic, caffeic, syringic, p-coumaric, ferulic, sinapic, and iso-ferulic acid) and four dimeric ferulic acids (diFA) (8-5′, 5-5′, 8-O-4′, and 8-5′-benzofuran diFA) were identified and quantified in cereal samples. Ferulic acid was detected as the predominant monomeric phenolic acid and 8-O-4′ diFA was the major dimeric ferulic acid. The results of total phenolic content (TPC) measured by Folin-Ciocalteau assay and antioxidant activity (AOA) evaluated by DPPH radical scavenging assay indicated that insoluble dietary fibre (IDF) alkaline extracts had significantly (p < 0.05) higher levels of TPC and AOA than WG and soluble dietary fibre (SDF) extracts for the same sample. Corn IDF with its higher levels of TPC, ferulic acid content, and AOA can be regarded as a potential antioxidant value-added functional food ingredient.

► Cereal insoluble dietary fibre (IDF) and soluble dietary fibre (SDF) were compared. ► IDF extracts showed better antioxidant capacities than whole grain and SDF. ► Yellow corn IDF extracts had highest antioxidant activity among cereals. ► Ferulic acid (FA) was the dominant acid in both the IDF and SDF of cereals. ► Iso-FA was identified as one of the major phenolics in a wide species of cereals.