Abstract: In order to make clear the causes of rice viscosity decline after 60Co-γ radiation,the morphological shape and stracture of starch granules of round-shaped rice radiated by 60Co-γ at different doses were observed with scanning electron microscope,and the alkali soluble protein segments,cooking viscosity and free radicals content were measured. The results indicated that the cooking viscosity of rice diclines straight from 213 to 21 with 60Co-γ dose inscreasing from 0 kGy to 15 kGy,the starch structure of rice are disintegrated,the proteins are cleaved into segments or peptide of 35 kD or less,and the free radicals content characterized by electron spin resonance(ESR) signal rises. 60Co-γ radiation causes excitation and ionization of electron of substance in rice from original orbit,thus free radicals that do not paire with electron are produced,and the reactions of the free radicals with starch and protein cause the cleavage of the latter. All these are the causes of rice viscosity decline induced by 60Co-γ radiation,as well as the structure disintegration of rice induced by the stress of starch and other components swelling from thermic effect of 60Co-γ radiation.

Key words: irradiation food, rice, viscosity of starch, radical, ESR