Inactivation of Toxoplasma gondii on blueberries using low dose irradiation without affecting quality

Toxoplasma gondii is a common protozoan parasite, whose environmentally-resistant stage, the oocyst, can contaminate irrigation water and fresh edible produce. Current washing steps in produce processing may not be effective for eliminating T. gondii from at-risk varieties of produce. The objective of this study was to evaluate low-dose irradiation as a means to inactivate T. gondii oocysts on blueberries. Blueberries (10 g) inoculated with T. gondii (5 log oocysts/g) were exposed to an absorbed dose of 0 (control), 0.2, 0.4 or 0.6 kGy gamma radiation at 4 degrees C. After treatment, oocysts were recovered from berries by washing, and excysted sporozoites were enumerated using a plaque assay. Vero cells were maintained as monolayers in a 6-well microplate, exposed to sporozoites recovered from berries, and incubated for 7 days to determine plaque-forming units (PFU). Immediately after treatment, blueberries without inoculated T. gondii were analyzed for compression firmness, surface color, and total anthocyanins. The results from this experiment demonstrate that the viability of T. gondii oocysts was significantly reduced after an irradiation treatment of 0.2 kGy. All treatments produced reductions of 4 log PFU/g beyond the detection limit of 1 log PFU/g. Quality analysis showed that there was no significant change in compression firmness, anthocyanins, or color in berries after the irradiation treatment. Results of this study indicated that low-dose irradiation is a potential intervention measure for controlling T. gondii contamination on blueberries without affecting product quality. Published by Elsevier Ltd.