Research – Impact of chlorinated water on pathogen inactivation during wheat tempering and resulting flour quality

Journal of Food Protection

Outbreaks of enteric pathogens linked to wheat flour have led the wheat milling industry to seek solutions addressing this food safety concern. Chlorinated water at 400-700ppm has been used in the flour milling industry as a tempering aid to control growth of yeast and mold in tempering bins. However, the effectiveness of chlorinated water for inactivating enteric pathogens on wheat kernels remained unknown. Five strains of Shiga-toxin producing Escherichia coli (STEC) and two strains of Salmonella were inoculated onto hard red spring wheat at 7 log CFU/g and stored at room temperature for 1-month. Inoculated wheat was tempered with four concentrations (0, 400, 800, 1200ppm) of chlorinated water (pH 6.5). The reduction due to chlorine was determined by calculating change in cell density at each chlorine level using the response at 0ppm as a reference. Uninoculated wheat tempered with chlorinated water was used to measure flour quality parameters. Changes in pathogen density over 18 hours ranged from -2.35 to -0.30 log CFU/g with 800ppm chlorinated water and were not significantly different from changes at 400ppm and 1200ppm. Significant (p< 0.05) differences in the extent of reduction were observed among strains. However, the effect of chlorinated water at reducing native microbes on wheat kernels was minimal, with an average reduction of 0.39 log CFU/g for all concentrations. No significant (p>0.05) changes occurred in flour quality and gluten functionality, or during breadmaking for grains tempered at 400 and 800ppm chlorinated water. There were small but significant (p<0.05) changes in flour protein content, final viscosity, and water absorption when tempered with 1200ppm chlorinated water. The data showed that the level of chlorinated water currently used in industry for tempering could reduce enteric pathogen numbers by 1.22 log CFU/g for STEC and 2.29 log CFU/g for Salmonella, with no significant effects on flour quality and gluten functionality.