SUMMARY This paper describes the pasteurization of liquid whole egg (LWE) using intense pulsed electric fields (PEF) combined with mild heat. Four kinds of liquids as solvents including carboxymethyl cellulose (CMC) solution, CMC solution with adding lipoproteins extracted from LWE (CMC+), LWE, and centrifuged LWE for reducing lipoproteins (LWE−) were compared for the effectiveness of the PEF pasteurization. The liquids including Enterobacter aerogenes (107 /mL) were subjected to a number of PEF with an amplitude of 30 kV/cm or 50 kV/cm. Pre‐ and post‐PEF thermal treatments with a temperature below 55 °C were used to enhance the killing effect. Our experiments show that the bacteria logarithmic reduction ratio of the pasteurization using 30 kV/cm PEF for CMC, CMC+, LWE, and LWE− were 6.6, 2.4, 1.4, and 1.6, respectively, whereas the reduction ratios were all more than 6 when the increased field of 50 kV/cm. Only bacteria in CMC solution were effectively killed compared to other liquids, which include lipoproteins, more or less. Numerical analysis of the electric field indicates the presence of lipoproteins in the vicinity of bacteria lessens the bacterial membrane potential, which results in weakening the killing effect.

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 55ºC 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 40ºC by means of an electrode cooling system. The iPEF combined with subsequent thermal energy of 55ºC reduced bacterial population by 6.6 Log 10 cycles or more, compared with a reduction of only 2.1 Log 10 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.

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