Transfer of Salmonella from Inert Food Contact Surfaces to Wheat Flour, Cornmeal, and NaCl

Salmonella contamination in a dry processing facility frequently requires removal methods that are nonaqueous. Removal of pathogens from food processing systems with a purge of uncontaminated dry food materials has been proposed; however, little is known with respect to efficacy. In this study, survival of Salmonella on inert contact surfaces and transfer of Salmonella from inert contact surfaces to low-moisture foods were evaluated. Six stainless steel and polymeric food contact material types, in bead form, were contaminated at 11 log CFU/mL and then stored at two temperatures, 25 and 4°C, for 6 months. Simultaneously, three dry food materials or ingredients were used to remove Salmonella from contaminated beads. Wheat flour, cornmeal, and NaCl (1 g each) were mechanically mixed with 3 beads of each material type. The rate of microbial transfer from contaminated beads to food materials was measured. Further experimentation using multiple transfers was applied on two representative beads types, 316 stainless steel and polypropylene, representing common surface contact materials used in processing equipment. Survival of Salmonella on beads depended on storage temperature, with longer survival (P < 0.05) at 4°C than at 25°C, but survival was not influenced by type of bead material. Transfer of Salmonella from stainless steel beads to flour was significantly greater (P < 0.05) than from plastic. Transfer rates from stainless steel to wheat flour, cornmeal, and NaCl were measured as -0.5713, -0.2592, and -1.4221 log CFU of Salmonella removed per cm2 per g of clean material used. Transfer rates from polypropylene to whole wheat flour, cornmeal, and NaCl were more than 10-fold lower at -0.0156, -0.0148, and -0.0129 log CFU of Salmonella removed per cm2 per g of clean material used. These results indicate that although material type may not influence Salmonella survival during storage, Salmonella is more easily removed from stainless steel than polypropylene.