Studies on maturation changes in fruits induced by ionizing radiation. II

Tomatoes (Licopersicon esculentum MILL. ) of three stages of maturity, mature green, breaker and light pink fruits were used in this experiment. Tomato fruits were irradiated with 60Co gamma rays at 0r, 5. 0×104r and 1. 0×106r at the rate of 2. 5×105r/hour. Temperatures during the irradiation and the storage were at about 20°C. The results obtained here were as follows:1. The pigmentation of tomatoes which were irradiated by gammarays at stages of breaker and light pink was delayed. The destruction of chlorophyll and the increasing of lycopene during ripening were apparently suppressed with higher doses. Gamma irradiation caused the considerable softening of the tissue immediately after irradiation. The subsequent change of softening in irradiated fruits was smaller than that in unirradiated ones. There was a decrease in protopectin in irradiated fruits immediately after irradiation. The titrative acidity and the amount of total sugar were not affected by gamma irradiation. The reduction of ascorbic acid by irradiation seemed to be greater in fruits of breaker stage than in those of light-pink.2. Carbon dioxide production of tomatoes irradiated at breaker stage increased with higher doses and this increased carbon dioxide production lowered to some extent at 24 hours after irradiation. These irradiated fruits exhibited the climacteric-like rise at the same period as that in unirradiated ones. Carbon dioxide production in tomatoes irradiated at light-pink stage was slightly greater than that in unirradiated ones, and light-pink fruits did not exhibited the climacteric like rise in both irradiated and unirradiated fruits.3. The effect of pyruvate and malate on carbon dioxide output in tissue slices increased in irradiated fruits more than in unirradiated ones. Gamma irradiation at 1.0×106r stimulated the ethylene formation. The increasing rate was higher in mature green fruits than in others. The rates of ethylene production decreased in all irradiated fruits 5 days after irradiation.4. The organoleptic evaluation showed the acceptability of the irradiated tomatoes lowered with the high dose.