Effect of water activity on the inactivation kinetics of Escherichia coli O157:H7 by electron beam in ground beef, chicken breast meat, and trout fillets

Water activity (a_w) of ground beef, chicken breast meat, and trout fillets was modified to intermediate (a_w 0.98–0.99) and lowest (a_w 0.94–0.96) levels. The meat samples with modified and unaltered (native, a_w 1.00) a_w were inoculated with Escherichia coli O157:H7 and subjected to electron beam (e‐beam). Survivor curves were plotted and the D₁₀‐values were calculated. The D₁₀‐values ranged from 0.22 kGy for trout at native a_w to 0.33 kGy for beef at intermediate, and chicken and trout at lowest a_w. Regardless of the species, a_w reduction increased E. coli resistance to e‐beam, suggesting that even small depletion of unbound water from food increases survival. The difference of the D₁₀‐values between the samples at intermediate and lowest a_w was insignificant. E‐beam could be used before a_w‐reducing techniques are applied to food products. However, this would require stringent microbial control following e‐beam processing. The ‘tailing’ of survivors was observed for some samples with reduced a_w.