Purpose: The objective of this study was to evaluate the effect of papain and bromelain on Tulane virus (TV) as evaluated by TV infectivity in cell culture.
Methods: TV was propagated in LLCMK2 cells in the absence of serum, filtered (0.2 um pore) from cell debris, and treated in duplicate trials (approximately 104 PFU/ml initial concentration) for two hours at 37°C with papain at 1,000 ppm or a combination of papain and bromelain at 500 ppm each. The effect of protease treatment on TV infectivity in LLCMK2 cells was evaluated by plaque assay in cell culture media M199 containing 10% fetal bovine serum to inhibit plant protease activity on host cells. Controls included untreated TV, TV treated at 37°C for 2h without papain or bromelain, uninoculated cell culture media, and uninoculated protease solutions held at 37°C for 2h.
Results: No reduction in TV infectivity was observed as a result of treatment by papain and bromelain at the conditions tested. TV was also stable to the mild heat treatment in the absence of plant proteases. Detection sensitivity was at least 10 PFU/ml.
Significance: Plant proteases, especially those with current applications in food processing, would make desirable antiviral agents for enhanced safety of raw produce and ready-to-eat foods. While the conditions tested did not reduce TV infectivity, additional treatment conditions to enhance enzymatic activity or in combination with other sublethal stresses are worthy of investigation.