Phytosanitary Irradiation Maintains Grape Quality under Simulated Transportation and Distribution Conditions

Table grapes are an important export crop, with California accounting for 98% of production within the United States and exporting more than 328,000 tons to over 60 different countries.  Currently, the most widely used phytosanitary treatment for grapes is methyl bromide fumigation. Irradiation can serve as an alternative to methyl bromide and is gaining use all over the world as a phytosanitary treatment for various fruit due to its efficacy on insects and maintenance of fruit quality.  The objective of this study was to monitor the effects of low-dose irradiation on the quality of 'Sugraone' and 'Crimson' seedless grapes treated at phytosanitary dose levels.  Grapes were irradiated at 400 Gy and stored at temperatures and times, simulating transport to Asia by sea and to Australia by air. Texture was the primary attribute affected by irradiation for both varieties of grapes, causing a loss of firmness. With respect to other attributes such as color, berry shatter, weight loss, and SSC/TA, there were significant differences in varietal response.  Sensory testing showed that consumers did not notice a difference in color, flavor, and texture on both days of sensory testing of 'Sugraone' or 'Crimson' berries, nor was there a preference in overall liking. Though analytical testing detected significant differences of some quality attributes, sensory testing revealed that consumers did not have a preference between treated and non-treated berries. Our results show that irradiation is an acceptable phytosanitary treatment for table grapes and presents a viable option for export to Asia and Australia.  The differences among grape varieties point to the importance of evaluating each variety for its response to irradiation treatment.