Processing temperature, alcohol and carbonation levels and their impact on pulsed electric fields (PEF) mitigation of selected characteristic microorganisms in beer

Beer was inoculated with Saccharomyces cerevisiae, Lactobacillus plantarum, Bacillus subtilis, and Salmonella Choleraesuis prior to pulsed electric fields (PEF) treatment at different levels of inlet temperature (≤ 4 °C pre-cooled and ≤ 14.7 °C ambient), alcohol (3.5 and 0.5%), and carbonation (degassed and carbonated). PEF was applied at the electric field strengths of 35–45, 35, and 35–40 kV/cm, with respective treatment times of 402–2296, 765, and 612–765 μs, and corresponding energy densities of 530–2339, 707, and 707–739 kJ/l to investigate its germicidal efficacy with regard to beer processing temperature (PT), alcohol content, and carbonation. In pre-cooled and ambient-temperature PEF-processed beer, reductions in microbial count of 4.0 (PT ≤ 40.7 °C) and up to 8.4 log10 (PT ≤ 68.7 °C) were achieved, respectively (P < 0.05); inactivation using ambient-temperature PEF processing was comparable to thermal pasteurization applied at 76 °C for 30 s (up to 8.3 log10 reduction in count (P ≥ 0.05)). Electric field strength and treatment time were fitted using a response surface model indicating higher PEF resistances of B. subtilis and S. Choleraesuis in beer (P < 0.05) while energy density and processing temperature gradients fitted for these microorganisms could allow optimization of PEF beer treatment. No difference in microbial inactivation due to alcohol and carbonation levels was obtained, except for higher reductions (P < 0.05) of L. plantarum in 3.5% beer and of S. Choleraesuis in carbonated beer.