Water soluble feruloyl arabinoxylans from rice and ragi: Changes upon malting and their consequence on antioxidant activity

Malting of rice and ragi is shown to bring about dynamic changes in water soluble feruloyl arabinoxylans (feraxans). Feraxans exhibited strong antioxidant activity, several folds higher than the expected activity due to their bound ferulic acid content and this is related to their molecular characteristics. The objective of this study is to determine the changes brought about by germination on water soluble feruloyl arabinoxylans (feraxans), one of the major components of soluble fibre from rice and ragi and their consequence on antioxidant activity. Soluble feraxans, isolated from native and malted rice and ragi were fractionated on DEAE-cellulose. Ferulic acid content of the major [0.1 molar ammonium carbonate (AC) eluted] fraction was higher in malts (rice: 1045 μg/g; ragi: 1404 μg/g) than in native (rice: 119 μg/g; ragi: 147 μg/g) and this fraction was separated by Sephacryl S-300 chromatography into two peaks each in rice (native: 232 and 24.4 kDa; malt: 75.4 and 39.6 kDa) and ragi (native: 140 and 15.4 kDa; malt: 38.9 and 15.4 kDa). 0.1 molar AC eluted fractions showed very strong antioxidant activity in vitro as determined by β-carotene–linoleate emulsion (IC 50: 0.16–0.24 mg), DPPH* (IC 50: 4.1–11.4 mg) and Ferric reducing/antioxidant power, FRAP (EC 1: 0.76–3.1 mg) assays. Antioxidant activity of feraxans was several (4.9–1400) folds higher than the expected activity due to their bound ferulic acid content. Apart from ferulic acid, presence of sugars with >C O (uronyl/acetyl) groups and degree/nature of glycan-polymerization were observed to influence antioxidant activity of the polysaccharides. Malting resulted in many dynamic changes in the ferulic acid content in different feraxan types and affected their antioxidant activity.