Antioxidant activities of corn fiber and wheat bran and derived extracts

The antioxidant activity of ground untreated corn fiber and wheat bran against lipid oxidation of rapeseed-fish oil-in-water emulsions was determined with respect to the formation of primary (lipid hydroperoxides) and secondary (propanal and hexanal) oxidation products. Corn fiber inhibited the formation of lipid hydroperoxides secondary products effectively at a concentration of 800 mg/kg emulsion, but wheat bran showed only low antioxidant effects. It was shown that the activity was based on the action of bound hydroxycinnamates like ferulic acid and p-coumaric acid, which was proven by the application of ferulated oligosaccharides (FOm) that showed higher activity than free ferulic acid on a molar basis. Enzymatic treatment with ferulic acid esterases did not increase the antioxidative activity. Extraction of corn fiber and wheat bran with methanol and isopropanol resulted in products which contained only low amounts of free soluble hydroxycinnamates and their marked activity against lipid oxidation and in antioxidant tests (TEAC, DPPH) gave reason for further fractionation. It has been shown that the polyaminconjugates diferuloylputrescine and p-coumaroyl-feruloylputrescine, which are major compounds of the corn fiber methanolic extract, exhibited high antioxidant activity and it can be assumed that they will take part in the antioxidant action of untreated fibers.

► Untreated corn fiber was most active in fish oil containing emulsions. ► Ferulated oligosaccharides inhibited the formation of oxidation products effectively. ► Antioxidant effects of ferulated oligosaccharides were higher than for ferulic acid. ► Polyaminconjugates, present in solvent extracts of corn fiber, showed high activity. ► Enzymatic treatment of fibers did not enhance their activity in emulsions.