Egg white proteins are quite susceptible to heat damage. It has been shown that pasteurization temperatures used by the industry today may decrease foaming properties of egg white. Liquid egg white is pasteurized at 56.7°C for 3.5 minutes. The industry also pasteurizes egg white using a combination of hydrogen peroxide and heat.
Injection of hydrogen peroxide into the holding tube allows for a lower pasteurization temperature at 51.7°C. The heat plus hydrogen peroxide method minimizes damage to egg white proteins. There is a continuing need to develop improved pasteurization methods for egg white. Pulsed electric field (PEF) has been proposed as a non-thermal method for inactivating pathogenic and spoilage organisms in food systems.
Very few studies have investigated the combination of heat and PEF as a pasteurization method. A new study by Amiali et al., 2006 (Journal of Food Science 71:M88-M94) evaluated the effect of heat in combination with PEF on inactivation of S. enteritidis (SE) and E. coli 0157:H7.
They inoculated egg white with 108 colony-forming units of E. coli 0157:H7 and SE. Inoculated egg white was treated with a continuous flow PEF system at 60 pulses (2µs width) using electric field intensities of 20 and 30 KV/cm. Temperatures used were 10°C, 20°C or 30°C.
The combination of PEF and heat provided a maximum inactivation of E. coli 0157:H7 cells of 1.7, 1.9 and 2.9 logs at 10°C, 20°C and 30°C, respectively. S.E. inactivations of 1.8, 2.6 and 3.7 logs were observed at 10°C, 20°C and 30°C. They found that the number of pulses was most important followed by temperature and electric field in providing inactivation of these two pathogens. There was a synergistic interaction of temperature and PEF on microbial inactivation in liquid egg white.
This research indicates some potential for using pulsed electric fields in combination with heat as a pasteurization method. Further studies varying the pulse rate and temperature to give a better log reduction perhaps warrant further study. For example, temperatures between 40° and 50°C in combination with PEF may provide better log reductions. It would be necessary to have a better log reduction than 3.7 logs for application of PEF by the egg products industry. As this non-thermal method is further considered, there is a need to investigate the effect of combined heat and PEF on functional properties.
