Validation of extrusion as a killing step for Enterococcus faecium in a balanced carbohydrate-protein meal by using a response surface design

Andreia Bianchini, Jayne Stratton, Steve Weier, Timothy Hartter, Brian Plattner, Galen Rokey, Gerry Hertzel, Lakshmi Gompa, Bismarck Martinez, Kent M. Eskridge

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


Outbreaks 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 carbohydrate-protein mix. 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°C). After the extruder was allowed to equilibrate for 10 min, samples were collected in sterile bags, cooled in dry ice, and stored at 4uC prior to analysis. E. faecium was enumerated with tryptic soy agar and membrane Enterococcus media, followed by incubation at 35uC 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 determination. Based on the results, the response surface model was y=185.04 - 3.11X 1 - 4.23X2 + 0.02X1 2 - 0.004X 1X2 + 0.08X2 2, with a good fit (R2 = 0.92), which demonstrated the effects of moisture and temperature on the inactivation of E. faecium during extrusion. According 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°C and moisture content of 28.1%. Other temperature and moisture combinations needed to achieve specific log reductions were plotted in a three-dimensional response surface graph.

Original languageEnglish (US)
Pages (from-to)1646-1653
Number of pages8
JournalJournal of food protection
Issue number9
StatePublished - Sep 2012
Externally publishedYes

ASJC Scopus subject areas

  • Food Science
  • Microbiology


Dive into the research topics of 'Validation of extrusion as a killing step for Enterococcus faecium in a balanced carbohydrate-protein meal by using a response surface design'. Together they form a unique fingerprint.

Cite this