Survival of Salmonella and Shiga toxin-producing Escherichia coli during tempering of wheat berries

Wheat flour contaminated with Salmonella or Shiga toxin-producing Escherichia coli (STEC) has been linked to foodborne outbreaks and recalls. The survival of five strains of rifampicin-resistant Salmonella and STEC on wheat berries was evaluated during tempering (hydration). Wheat berries were inoculated with Salmonella (cocktail) or STEC (individual strains or cocktail) and dried at ambient conditions for 24 h. Sterile water (control), lactic acid (LA; 5.4 or 10.9%) or peracetic acid (PAA; 100 or 500 ppm) was added and then samples were held at 15, 23, or 30 degrees C for up to 24 h. Significant population reductions were observed after addition of LA or PAA (time 0 h), with small but significant additional declines occurring between 0 and 12 h but not between 12 and 24 h. Salmonella populations declined 0.43 and 1.79 log CFU/g on wheat berries tempered at 23 degrees C for 12 h with sterile water and 5.4% LA, respectively. Similar 12-h reductions of 0.45-0.80 log CFU/g (water) and 1.43-1.68 log CFU/g (5.4% LA) were observed for the STEC cocktail. Increasing LA to 10.9% during tempering resulted in significantly greater reductions (1.87-2.03 log CFU/g) of STEC after 12 h; similar reductions were observed for individual STEC isolates (1.74-2.14 log CFU/g). Reductions of STEC during 12 h of tempering were 1.70 and 1.78 log CFU/g with 10.9% LA at 15 degrees C and 30 degrees C, respectively, and 0.73 and 1.21 log CFU/g with 100 and 500 PAA, respectively at ambient conditions. Addition of LA or PAA during tempering may provide a tool to reduce Salmonella or STEC in wheat.

Automated summary

The addition of lactic acid or peracetic acid during tempering reduces the population of Salmonella or STEC on wheat berries.