The effects of irradiation on 'Hayward' kiwifruit

Abstract

The responses of 'Hayward' kiwifruit towards a range of low and medium dose irradiation treatments were assessed in terms of the quality parameters knows to be important in the marketing of this fruit. The levels of CO2 and C2H4 produced from kiwifruit immediately following irradiation treatment increased and then fluctuated throughout the 12 hours of sampling at ambient temperatures. Over-night storage for 12 hours at ambient temperatures resulted in a reduction in the production of both gases and after coolstorage at 0°C, levels of C2H4 and CO2 from irradiated and not-irradiated fruit were at similar low levels. Analysis of L-ascorbic acid and dehydroascorbic acid in kiwifruit over two seasons showed conclusively that there was no loss of this vitamin from the low or medium dose irradiation treated fruit, either immediately following treatment or after a range of storage periods. Testing of irradiated fruit for a loss of texture as a possible indication of cellular damage showed no significant difference in penetrometer readings between irradiated and non-irradiated fruit. However, significant differences between control and medium dose treated fruits were found in the weight lost during storage. The differences recorded were not restricted to a particular treatment group, with variations arising in the response to both treatment and the length of the storage periods. The use of X-ray electron spectroscopy to detect damage to the skin of kiwifruit did not give any indication of damage to the cells of the outer surface layer. Studies on possible changes to the flavour of kiwifruit after irradiation treatments using gas chromatography and mass spectrometry showed differences in the volatile profiles between non-irradiated fruit and fruit treated with 1500-2000 Gy irradiation. There were no changes in the levels of titratable acids. Botrytis cinerea proved to be very resistant to irradiation and lethal effects could only be achieved at does levels beyond the physiological tolerance of the fruit. There was an indication of increased growth of fungal spores after irradiation treatments at 1000 and 2000 Gy.