Comparison of the effect of radiation of various penetrating powers on the damage to citrus fruit peel

Parts of a single harvest of mature Shamouti oranges were irradiated with 25-240 Krad doses offour kinds of ionizing radiation: ⁶⁰Co γ-rays, 0·5 MV (surface) electrons or 1·5 MV (deep) electrons applied uniformly to the whole surface, and 1·5 MV (localized) electrons applied to either stem or stylar end or to the equatorial region of non-rotating fruits. Surface and deep electrons caused significantly more peel damage than γ-rays. The extent of peel damage was similar after 2 and 4 weeks storage. Damage appeared only on that portion of the peel that had been irradiated; it was much more extensive at the stem end than at the stylar end. The dose-absorption profiles of the four irradiation treatments within the peel layers differed markedly from each other, but their effects on flavedo ascorbic acid, reducing sugars, catalase and peroxidase activities were in general similar. The mature fruit of this experiment was less sensitive for these parameters than fruits picked earlier in the season.