Abstract:The relationship between radical production and oxidative properties of rice protein under microwave irradiation was investigated. Electron spin resonance (ESR) studies proved that the radicals produced in the microwaved rice protein samples were carbon-centered. Comparative studies revealed that radicals were not only produced in thermally treated materials, but also in small quantities in native samples of rice protein. Under microwave irradiation, the ESR signals for radicals gradually increased with the reduction of water activity as well as with the increase of microwave power. With the increase of irradiation time, the intensities increased, and the rate of increase of intensities of radical signals also increased. By measuring the surface hydrophobicity and the contents of carbonyl, sulfhydryl, and free amino groups, it was found that the internal hydrophobic side-chains of the protein were exposed and some of the peptide bonds were broken. Combined with the production of radicals during microwave irradiation, it was proposed that when microwaved to over 80 °C, the increase rate of production of carbon-centered radicals would be significantly higher, and was consistent with oxidation characteristics.
