Dry-pasteurization of egg albumen powder in a fluidized bed

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Hot room pasteurization of dried egg albumen has been utilized by the egg processing industry for a number of years. This practice to assure Salmonella-free egg albumen is time-consuming and requires considerable storage area. New studies by Hammershoj et al., 2006, (Journal of Food Science and Technology 41:249-261 and Journal of Food Science and Technology 41:263-274) propose a fluidized bed process to pasteurize dried egg albumen. This process would force hot air or gas through a bed of albumen solids at a velocity to overcome gravity and suspend the particles in a fluidized manner. The close contact with the hot air would provide a high heat transfer and allow for a faster heat treatment. Fluidized beds are used in the food processing industry to dry, cool, freeze and agglomerate food products.

The first paper investigated the effect of a fluidized bed process on bacterial, physical and chemical properties. In their first experiment they investigated at temperatures of 90°C and 130°C at a relative humidity of 2-3%. Experiment 2 used two different relative humidity levels of 2% and 20% and a fixed temperature of 113°C. The higher relative humidity gave a much greater bacterial elimination and an increased surface hydrophobicity indicating more protein unfolding, which would likely improve functional properties. They indicated that using temperatures of 115°-130°C for 1 to 2 hours at high moisture levels gave bacterial elimination (total plate counts) comparable to that achieved with traditional pasteurization. They noted some discoloration (darker and more yellow) of the albumen powder which may have been a result of the Maillard reaction. They postulated that perhaps the desugaring was not complete. These scientists also noted an increased particle size, particularly at the high relative humidity which may have been due to agglomeration.

The second paper evaluated the effect of fluidized bed treatment on functional properties. They observed that gels prepared from powders treated at higher temperatures and higher relative humidity had higher stress and strain and better water holding capacity. Foaming capacity was improved at a higher air moisture level. Foam stability was improved by increasing surface pressure.

These authors concluded that fluidized bed technology has potential for pasteurization of dried egg albumen. There is a need to investigate further the effect of this process on color. Also, the effectiveness for eliminating Salmonella needs further study. Investigation of other times and temperatures may also need further investigation. This technology appears to hold some promise and needs additional consideration. (Dr. Glenn W. Froning, Professor Emeritus, Department of Food Science and Technology, University of Nebraska, Lincoln, Nebraska 68583-0919)

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