SUMMARYTextural changes of pears and peaches exposed to gamma radiation of 300, 600, and 900 Krads were found to correspond to a decrease in proto‐pectin content and an increase in pectin and pectate fractions of the fruits. Characterizations of the 700 alcohol‐insoluble solids prepared from these fruits revealed only minor differences in respect to their anhydrouronide and acetyl content and degree of esterification. To account for the marked effects of radiation, activities of pectic enzymes extracted from irradiated fruits were investigated. Pectin methylesterase showed an increased activity immediately after doses of 300 and 600 Krads, and enzymes extracted from fruit four days after irradiation had a reduced activity. Pears, peaches, and nectarines irradiated under nitrogen atmosphere softened much less than fruits irradiated under air. While this may be attributed to the reduced formation of free radicals under anoxic conditions, a further experiment with pectin solutions exposed to gamma radiation under similar atmospheric conditions did not support this suggestion. The changes in 1 pectin solutions were related to radiation dose, but were remarkably similar regardless of the presence or absence of oxygen during expos
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