of Salmonellosis and recalls of
low-moisture foods including extruded products highlight the need for the food and
feed industries to validate their extrusion processes to ensure the destruction
of pathogenic microorganisms. Response surface methodology was employed to study
the effect of moisture and temperature on inactivation by extrusion of Enterococcus faecium NRRL B-2354 in a
balanced carbohydrate-protein mix was formulated to different combinations of
moisture contents, ranging from 24.9% to 31.1%, and each was inoculated with a
pure culture of E. faecium to a final
level of 5 log CFU/g. Each mix of various moistures was then extruded in a
pilot scale extruder at different temperatures (ranging from 67.5 to 85 degrees C).
After the extruder was allowed to equilibrate for 10 minutes, samples were
collected in sterile bags, cooled in dry ice and stored at 4 degrees C prior to
E. faecium was enumerated
with tryptic soy agar and membrane Enterococcus
media, followed by incubation at 35 degrees C for 48 h. Each extrusion was repeated
twice, with the central point of the design being repeated four times. From
each extrusion, three subsamples were collected for microbial counts and moisture
to the response surface analysis, the greatest reduction of E. faecium for the inoculation levels
studied here (about 5 log) in a carbohydrate-protein meal would occur at the
temperature of 81.1 degrees C and moisture content of 28.1%.
Source: A. Bianchini et al., 2012. Validation of extrusion as
a killing step for Enterococcus faecium
in a balanced carbohydrate-protein meal by using a response surface design. J Food Prot 75: 1646–1653. doi:10.4315/0362-028X.JFP-12-085
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