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P1-115 Optimization of Extrusion for the Inactivation of Enterococcus faecium NRRL-B2354 Using a Response Surface for Moisture and Temperature

Monday, July 23, 2012
Exhibit Hall (Rhode Island Convention Center)
Andreia Bianchini, University of Nebraska , Lincoln , NE
Jayne Stratton, University of Nebraska , Lincoln , NE
Steven Weier, University of Nebraska-Lincoln, Lincoln, NE
Brian Plattner, Wenger Manufacturer, Sabetha, KS
Galen Rokey, Wenger Manufacturer, Sabetha, KS
Gerry Hertzel, Wenger Manufacturer, Sabetha, KS
Tim Hartter, Wenger Manufacturer, Sabetha, KS
Lakshmi Gompa, University of Nebraska-Lincoln, Lincoln , NE
Bismarck Martinez, University of Nebraska-Lincoln, Lincoln , NE
Introduction:  Outbreaks of salmonellosis and multiple recalls of low moisture foods including extruded products highlight the need for industry to validate their extrusion processes to ensure the destruction of pathogenic microorganisms.  The use of surrogate organisms allows for studies to be conducted with safer organisms than pathogens. Enterococcus faecium NRRL B-2354 has been previously reported as an appropriate surrogate for Salmonella for the validation of thermal processes in almonds and was used in this study to validate the extrusion process for inactivation of Salmonella enterica.

Purpose:  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 carbohydrate-protein mix.

Methods:  A balanced carbohydrate-protein mix was formulated to different combinations of moisture contents ranging from 25.8 to 31.1% and each was inoculated with a pure culture of Enterococcus faecium NRRL-B2354 to a final level of 5 logs or above.  Each mix of varying moistures was then extruded in a pilot scale extruder at different temperatures (set points ranging from 65°C to 85°C).  At each combination of moisture and temperature the extruder was allowed to equilibrate for 10 minutes before sample collection.  Samples were collected in sterile bags, cooled in dry ice, and stored at 4°C prior to analysis.  E. faeciumwas enumerated using TSA and mEnterococcus media followed by incubation at 35°C for 48 hours.  Each extrusion was repeated twice, with the central point of the design being repeated four times.  From each extrusion, 3 subsamples were collected for microbial counts and moisture determination.

Results:  Based on the response surface analysis of the results, temperature and moisture combinations above 77°C and 28% moisture would completely eliminate E. faecium, with the main factor being temperature.  Other temperature and moisture combinations needed to achieve specific log reductions were plotted in a three-dimensional response surface graph that can be referenced by industry.  Decreasing moisture and temperature combinations resulted in higher survivability of the microorganism.

Significance:  The response surface model showed a very good coefficient of correlation (above 0.9) with temperature having a significant effect on the survivability of E. faecium NRRL-B-2354 during extrusion.  The response surface model gives industry a tool to better understand the effect of moisture and temperature on the inactivation of heat resistant microorganisms in their processes.

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