Abstract— This study focuses on the fact that the chemiluminescence in the visible region is emitted from the H2O2/gallic acid/ horseradish peroxidase (HRP) and the H2O2/gallic acid acetaldehyde (MeCHO) systems. The concentration dependence of chemiluminescence intensity that led to the different response of HRP and MeCHO toward H2O2 indicates that the photon emission participates with peroxidase activity including an electron transfer reaction. From our experimental results, in this study, we postulated a reaction process for chemiluminescence based on a one‐electron redox shuttle from H2O2 by peroxidase. The photon intensity and spectra data from the H2O2/ HRP and the H2O2/MeCHO systems with various cate‐chins were not only affected by HRP and MeCHO but also corresponded with the chemical structure of cate‐chins. The energy calculated from the spectra is 47–64 kcal/mol. These results suggested that the chemiluminescence of both systems arose from excited carbonyl compounds produced by an intermediate of the alkyl radical and the metal‐bound hydroxyl (compound II species). Hydroxyl radical inhibition, showing a notable increase from the gallic acid addition, makes the decay of the hydroxyl form of heme iron the most likely candidate for the chemiluminescence.

The chemiluminescence (CL) constituents of cereals were detected by CL using the H(2)O(2)-acetaldehyde system. The cereals tested, such as rice, millet and sorghum, exhibited various levels of CL activity. The gamma-oryzanol fraction was extracted from brown rice and separated into four constituents by HPLC. The four constituents were identified as cycloartenyl ferulate, 24-methylenecycroartanyl ferulate, campesteryl ferulate and beta-sitosteryl ferulate. Free radical scavenging activities with 1,1-diphenyl-2-picrylhydrazyl (DPPH) and CL intensities of four constituents (gamma-oryzanol components) were measured and compared with that of gallic acid, which is a typical free radical scavenger. Four constituents scavenged DPPH radicals and scavenging activities were proportional to CL intensities. Concentrations of four CL constituents required to quench 50% (IC(50)) of the free radicals ranged from 0.9 to 1.1 mmol/L. We demonstrated that measurement of CL intensities was a rapid and convenient method for screening DPPH radical scavenging activities of rice.

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