Antioxidant activity of rye bran alkylresorcinols and extracts from whole-grain cereal products

The antioxidant properties of rye bran alkylresorcinols (C15:0–C25:0) and extracts from whole-grain cereal products were evaluated using their radical-scavenging activity on DPPH and the chemiluminescence method (CL). DPPH radical reduction varied from ∼10% to ∼60% for the alkylresorcinol homologues at concentrations from 5 to 300 μM and was not dependent on the length of the alkyl side chain of the particular homologue. Differences in the EC50 values for the studied compounds were not statistically significant, the values varying from 157 μM for homologue C23:0 to 195 μM for homologue C15:0. Moreover, values of EC50 for all the alkylresorcinol homologues were significantly higher than those for Trolox and α-, δ-, and γ-tocopherols, compounds with well-defined antioxidant activity and used as positive controls. CL inhibition was evaluated for all the tested alkylresorcinol homologues at concentrations of 5 and 10 μM and varied from ∼27% to ∼77%. Similar to the DPPH method, the slight differences in CL inhibition suggest that the length of the alkyl side chain had no major impact on their antioxidant properties. The extracts from whole-grain products were added to the DPPH and CL reaction systems and their antioxidant activities were tested and compared with the total amount of alkylresorcinols evaluated in the extracts. DPPH radical and CL reduction for the whole-grain products varied from ∼7% to ∼43% and from ∼37% to ∼91%, respectively. A clear relationship between DPPH radical and CL reduction levels and the amount of total alkylresorcinols was obtained for whole-grain breakfast cereals, in which the reduction level decreased in the order rye > wheat > mixed > barley. Therefore it may be considered that the antioxidant activity of alkylresorcinols could be of potential importance to the food industry, which is continuously searching for natural antioxidants for the protection of food products during their processing and storage.