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Weekly UpdatesGood news for fans of raw cookie dough. USDA-ARS researchers have filed a patent application on a crossflow microfiltration (CMF) membrane separation technique that can protect pasteurized liquid eggs from naturally occurring spoilage bacteria and pathogens, such as S. enteritidis, the primary cause of egg-related foodborne illness in the United States. The technology has also been successfully applied to milk.
CMF removes more pathogens than thermal pasteurization does. And it does so without affecting the eggs' ability to foam, coagulate and emulsify--meaning that CMF-treated eggs could be safely substituted for pasteurized eggs in products where those characteristics are desired, such as angel food cake and mayonnaise.
In a pilot-scale study, CMF removed 99.9999% of inoculated S. enteritidis from unpasteurized liquid egg whites. CMF can also remove B. anthracis spores from egg whites. USDA researchers had used CMF to remove 99.9999% of B. anthracis spores inoculated into fluid milk. Microfiltration can also protect milk from more common bacterial pathogens, potentially extending its shelf life. CMF works best when treated as an accompaniment to pasteurization, not as a replacement for it. Combining the two processes significantly reduces the pathogen load.
In each of 16 trials, unpasteurized liquid egg white containing approximately 6.0 log10 CFU per ml of total aerobic bacteria was wedge-screened, homogenized and diluted with deionized water (1:2 w/w). The water contained 0.5% sodium chloride to lower the viscosity of the liquid egg white and subsequently facilitate microfiltration.
Next, the researchers adjusted the liquid egg white pH to 6.0, 7.0, 8.0 or 9.0. Then the samples were inoculated with approximately 7.0 [log.sub.10] CFU per ml of a five-strain cocktail of S. enteritidis before undergoing microfiltration at 25 C or 40 C using a ceramic membrane with a nominal pore size of 1.4 mm at a crossflow velocity of 6 meters per second.
Permeate flux was maximum at the lowest pH studied--pH 6. But temperature had little influence on the flux at any value of pH studied. Salmonella levels were reduced to below the detection limit of less than 0.5 [log.sub.10] CFU per ml using the direct plating method. In addition, there was no subsequent outgrowth of any remaining cells of the pathogen for up to 21 days at 4 C. Only about a 0.7 [log.sup.10] CFU per ml increase occurred when the samples were stored at 10 C.
Further information. Sudarsan Mukhopadhyay, USDA-ARS Eastern Regional Research Center, 600 E. Mermaid Lane, Wyndmoor, PA 19038; phone: 215-233-6600; fax: 215-233-6581; email: sudarsan.mukhopadhyay@ars.usda.gov.
About 40,000 cases of salmonellosis are reported in the United States each year. Now, scientists believe that the new technology can compensate for the shortcomings of thermal pasteurization.
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