Effect of irradiation on the post-harvest quality of pears

Summary of research conducted 2004 to 2007 :

The project comprised four main objectives, namely: (i) to establish the effect of cobalt-60 irradiation on storage quality of pears, (ii) to determine the minimum and maximum absorbed irradiation dose in a pallet of pears, (iii) to test methods to reduce the irradiation dose ratio, and (iv) to ascertain whether SmartFresh^SM application prior to packing can maintain flesh firmness of irradiated pears.

(i)  Three populations each of Forelle and Packham Triumph’s pears stored either under regular atmosphere, or controlled atmosphere conditions prior to packing, were irradiated within 7 days after packing with cobalt-60 at different dosages, ranging from 600 to 2500 Gy. One population of Beurre Bosc pears was irradiated from 600 to 900 Gy. Pears were evaluated after storage for 8 weeks at -0.5°C, followed by 7 days at 20°C.

No populations of Forelle and Packham Triumph, as well as Beurre Bosc pears, were adversely influenced by irradiation ranging between 600 to 900 Gy, after storage for 8 weeks at –0.5°C followed by 7 days at 20°C. Although flesh firmness was in some cases lower in irradiated than non-irradiated pears, the levels generally conformed and were acceptable according to overseas supermarket standards.

(ii & iii) A minimum: maximum absorbed irradiation dose ratio of 1:3.5 was obtained when a pallet of Forelle pears (12.5 kg cartons stacked five layers high) was irradiated. The ratio was reduced to 1:2.3 when the middle cartons of the stack were removed, or when a 3-layered stack of pears was elevated, by placing three empty pallet bases below the stacked cartons. If a larger cobalt-60 source could be used, the minimum-maximum absorbed irradiation dose ratio in a stacked pear pallet may be further reduced. This aspect of the project will need to be further investigated if required.

Summary of 2008 research :

• The effect of SmartFresh^SM on two Forelle pear populations, irradiated at 900 Gy, was evaluated during the 2008 season. SmartFresh^SM was applied at the commercial concentration and rate in metal containers at intake. Fruit were examined after a storage period of 8 weeks at –0.5°C, and 8 weeks at –0.5°C + 7 days at 20°C.

In both Forelle populations, flesh firmness of irradiated pears was significantly firmer when treated with SmartFresh^SM, in comparison to pears not treated with SmartFresh^SM, after storage for 8 weeks at -0.5°C + 7 days at 20°C. Skin ground colour in both Forelle populations irradiated at 900 Gy was significantly less advanced in SmartFresh^SM treated fruit than those not treated with SmartFresh^SM. Other storage disorders were not influenced by the treatments.

The results showed that if irradiation technology is used on Forelle pears, SmartFresh^SM treated fruit can be used to reduce loss in flesh firmness, and to maintain skin ground colour during storage.