Increase temperature to optimize microbial reduction.

Egg-related outbreaks of Salmonella and an awareness of the potential for Listeria contamination have heightened concerns for the safety of egg products. Heat pasteurization is typically used by the food industry to assure the microbial safety of liquid whole egg (LWE). The use of pulsed electric fields (PEFs) for pasteurizing LWE or liquid egg white (LEW) has been studied, but has resulted in a limited reduction of pathogens.

USDA scientists wanted to see if changing egg pH or increasing the treatment temperature would make PEF technology more effective in inactivating pathogens. They found that the effectiveness of the treatment depended on the pH of liquid eggs. Increasing treatment temperature at neutral pH would enhance the effectiveness of PEF treatment.

In their tests, the researchers inoculated S. typhimurium, S. enteritidis and L. monocytogenes cells into LWE or LEW. They adjusted the pH of samples to pH 6.6, 7.2 or 8.2. The investigators used treatment temperatures of 15 C, 25 C, 30 C or 40 C.

The scientists applied PEF process conditions: a field strength of 25 kV per cm, a pulse duration of 2.1 [micro]s, a total treatment time of 250 [micro]s, a pulse repetition of 200 pulses per second and a flow rate of 1 mL sec. The non-treated control and treated samples containing S. typhimurium and S. enteritidis were plated onto tryptic soy agar, and the sample containing L. monocytogenes was plated onto brain-heart infusion agar and incubated at 35 C for 24 hours.

Researchers found that treatment temperatures--15 C and 25 C--did not affect the inactivation of S. typhimurium, S. enteritidis and L. monocytogenes in LWE at pH 6.6. However, levels of S. typhimurium cells in LWE at pH 7.2 were reduced by 2.1 logs at 40 C and by 1.8 logs at 30 C. The scientists obtained 1.3-log and 0.6-log reductions of S. typhimurium in LEW at pH 8.2 at 25 C and 15 C, respectively.

Further information. Tony Jin, USDA-ARS Eastern Regional Research Center, Room 3028, 600 E. Mermaid Lane, Wyndmoor, PA 19038; phone: [phone]; fax: [phone]; email: [e-mail].