The total protein content of the purified VLP preparation was determined using the Pierce BCA Protein Assay (Thermo Science, Rockford, USA). Endotoxin levels in the VLP preparations were quantified using the Limulus amebocyte lysate (LAL) assay (Lonza, Walkersville, MD, USA). The level of endotoxin was\0.1 EU/10 lg of protein, which is below the international standard of B30 EU/20 lg of protein [15] . All samples were analyzed for protein expression by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blot. The presence of NoV VLPs was verified by electron microscopy (EM). VLP preparations were negatively stained with 3% uranyl acetate (UA), pH 4.6. The VLPs were examined using an FEI Tecnai F12 electron microscope operating at 120 kV.