US: Irradiation good for grapes, blueberries

New research reveals that phytosanitary irradiation which is currently being used to treat fruits such as guava, rambutan and mango, can be effective in preserving the quality of blueberries and grape during long-distance transportation, distribution, storage.

Scientists in the US monitored the effects of irradiation on the quality of three varieties of blueberries and two varieties of grapes treated at phytosanitary dose levels. Results showed that blueberries and grapes have a high tolerance for phytosanitary irradiation and that storage affects quality more than irradiation. Firmness was the primary attribute affected by irradiation for both varieties of grapes.

It is often necessary to treat produce for insects in order to transport crops out of quarantine areas. Yet fumigation with methyl bromide, one of the most common treatments, is being phased out because of its depleting effect on the ozone layer. Phytosanitary irradiation is a promising alternative.

'Star', 'Jewel', and 'Snowchaser' blueberries and 'Sugraone' and 'Crimson Seedless' grapes were irradiated at a target dose of 400 Gy (range of 400-590 Gy for blueberries and 400-500 Gy for grapes) and stored for 3 and 18 days under refrigeration, plus 3 days at ambient temperatures. "This experiment was designed to simulate the time of ground transport (from California) to Mexico and sea transport from California to Asia," the scientists explained. The fruit was then evaluated for soluble solids concentration, titratable acidity, and weight loss. With respect to these quality attributes, the results showed differences among fruit varieties, but the researchers found treatment effects to be "not significant."

The study also involved sensory tests in which consumers evaluated the fruit on appearance, flavor, texture, and overall "liking." "Firmness was the primary attribute affected by irradiation for both varieties of grapes, but sensory testing showed that consumers did not have a preference for control or irradiated fruit," the authors said. "However, sensory scores for flavor were higher for the irradiated berries than the control berries after storage, suggesting a decline in quality of the control blueberries with time," the scientists noted.


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