Inactivation of enterobacter aerogenes in carboxymethyl cellulose solution using intense pulsed electric fields (iPEF) combined with moderate thermal treatment

This paper describes low-temperature sterilization of Enterobacter aerogenes in carboxymethyl cellulose solution using intense pulsed electric fields (iPEF) combined with moderate thermal energy. The bacterial suspension was exposed to moderate temperatures of up to 55°C for 2 minutes after tens of 530 ns-long, 50 kV/cm pulses in a single-pass continuous flow system. Suspension temperatures at the entrance and exit of the iPEF exposure chamber were maintained at 40°C by means of an electrode cooling system. The iPEF combined with subsequent thermal energy of 55^oC reduced bacterial population by 6.6 Log10 cycles or more, compared with a reduction of only 2.1 Log10 cycles by iPEF without heat treatment. Sterilization effects increased with increasing thermal treatment temperature and pulse number. Results obtained after culturing the iPEF-exposed bacteria in NaCl rich agar, which hinders the reorganization of the damaged membrane, implies that even bacteria surviving the iPEF exposure are damaged to some extent though may later recover. Bacteria were made vulnerable to subsequent thermal treatment by iPEF-induced membrane damage. This indicates that moderate thermal stress after iPEF exposure increases sterilization effects.