Antioxidant Properties of Aqueous Extract of Roasted Hulled Barley in Bulk Oil or Oil-in-Water Emulsion Matrix

Antioxidant properties of the aqueous extracts of hulled barley (Hordeum vulgare L.) that had been roasted at 210 degrees C for 20 min were determined in bulk oil and oil-in-water (O/W) emulsions. Bulk oils were heated at 60, 100, and 180 degrees C, and O/W emulsions were oxidized under riboflavin photosensitization. The content of phenolic compounds was analyzed by high-performance liquid chromatography, and in vitro antioxidant assays were also conducted. The major phenolics contained in the aqueous extract of roasted hulled barley (AERB) were p-coumaric, ferulic, protocatechuic, chlorogenic, 4-hydroxybenzoic, and vanillic acids. Depending on the concentration and oxidation temperature, AERB had antioxidant or prooxidant properties in bulk oil. At 60 degrees C, AERB at a concentration of 0.5% acted as a prooxidant, whereas at 1.0% it acted as an antioxidant. At 100 degrees C, AERB acted as an antioxidant irrespective of concentration. In 180 degrees C conditions, 0.5% AERB acted as a prooxidant, whereas other concentrations of AERB acted as antioxidants. In the case of riboflavin photosensitized O/W emulsions, AERB showed antioxidant properties irrespective of concentration. Antioxidant abilities of AERB are affected by the food matrix, including bulk oil and O/W emulsions, and concentrations of AERB, even though diverse phenolic compounds may display high antioxidant properties in in vitro assays.