Inactivation of Toxoplasma gondii on Blueberries Using Low-dose Irradiation

Introduction: Toxoplasma gondii is the most common parasite that contaminates produce. However as more cases of T. gondii contamination are being linked to produce, current washing steps in produce processing may not be effective or suitable for some varieties of produce.  

Purpose: The objective of this study was to evaluate the effect of low-dose irradiation on inactivating T. gondii oocysts on blueberries. 

Methods: 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 at 4°C.  A self-contained Lockheed Corporation ¹³⁷CS gamma radiation source at a dose rate of 0.075 kGy/min was utilized.  After treatment, oocysts were recovered from berries.  Human foreskin fibroblast (HFF) cells were maintained as monolayers in a 96-well microplate, exposed to excysted T. gondii recovered from berries, and incubated for 7 days. The viability of HFF cells was evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium (MTT) assay. In addition, blueberries were analyzed for compression firmness, surface color, and total anthocyanins, immediately after each treatment. 

Results: HFF cells inoculated with oocysts recovered from the 0.6 kGy treated berries retained viability at 93% compared to the control, indicating that treated oocysts were less infectious to HFF cells. The result showed that gamma radiation significantly (P < 0.05) inactivated T. gondii oocysts on blueberries. Quality analysis showed that there was no significant change in texture, anthocyanins, or color in berries after the irradiation treatment

Significance: Findings of this study indicated that low-dose irradiation is a potential intervention measure for controlling T. gondii contamination on blueberries without affecting product quality.