Evaluation of methods for inoculating dry powder foods with salmonella enterica, enterococcus faecium, or cronobacter sakazakii

Justin R. Wiertzema, Christian Borchardt, Anna K. Beckstrom, Kamal Dev, Paul L Chen, Chi Chen, Zata M Vickers, Joellen M Feirtag, Laurence Lee, R. R Ruan, David J Baumler

Research output: Contribution to journalArticle

Abstract

Salmonella and Cronobacter are two bacteria of concern in powdered food ingredients with low water activity, due to their ability to remain viable for long periods of time. There is great interest in studying the survival of these bacteria in powdered foods, but discrepancies have been reported between broth-grown and lawn-grown bacterial cells and their thermal resistance and desiccation tolerance once inoculated onto powdered foods. The purpose of this study was to evaluate three different powdered food inoculation methods, two broth-grown and one lawn-grown. To evaluate these methods on three types of powdered food matrices, Salmonella enterica serovar Typhimurium LT2 (ATCC 700720), Salmonella surrogate Enterococcus faecium (NRRL B-2354), and Cronobacter sakazakii (ATCC 29544) were inoculated onto nonfat dry milk powder, organic soy flour, and all-purpose flour using one of the three previously developed inoculation methods. In the first broth-grown method, labeled broth-grown pelletized inoculation, a bacterial cell pellet was added to powdered foods directly and mixed with a sterile wooden stick. The second broth-grown method, labeled broth-grown spray inoculation, used a chromatography reagent sprayer to spray the bacterial cell suspension onto the powdered foods. The third inoculation method, lawn-grown liquid inoculation, made use of a spot inoculation and a stomacher to incorporate each bacterium into the powdered foods. Results indicated that the method of inoculation of each powder impacted repeatability and bacteria survivability postequilibration (4 to 6 days). Brothgrown spray inoculation, regardless of the powder and bacterium, resulted in the highest log reduction, with an average ~1-log CFU/g reduction following equilibration. Broth-grown pelletized inoculation resulted in the second-highest log reduction (~0.79 log CFU/g), and finally, lawn-grown liquid inoculation was the most stable inoculation method of the three, with ~0.52- log CFU/g reduction. Overall, the results from this inoculation study demonstrate that inoculation methodologies impact the desiccation tolerance and homogeneity of C. sakazakii, E. faecium, and Salmonella Typhimurium LT2.

Original languageEnglish (US)
Pages (from-to)1082-1088
Number of pages7
JournalJournal of food protection
Volume82
Issue number6
DOIs
StatePublished - Jun 1 2019

Fingerprint

powdered foods
Cronobacter sakazakii
Enterococcus faecium
Salmonella enterica
Powders
powders
inoculation methods
Food
Bacteria
bacteria
Desiccation
Flour
methodology
Salmonella Typhimurium
Salmonella
Cronobacter
dried skim milk
liquids
soy flour
food matrix

Keywords

  • Cronobacter
  • Enterococcus
  • Inoculation
  • Low moisture
  • Salmonella

PubMed: MeSH publication types

  • Journal Article

Cite this

Evaluation of methods for inoculating dry powder foods with salmonella enterica, enterococcus faecium, or cronobacter sakazakii. / Wiertzema, Justin R.; Borchardt, Christian; Beckstrom, Anna K.; Dev, Kamal; Chen, Paul L; Chen, Chi; Vickers, Zata M; Feirtag, Joellen M; Lee, Laurence; Ruan, R. R; Baumler, David J.

In: Journal of food protection, Vol. 82, No. 6, 01.06.2019, p. 1082-1088.

Research output: Contribution to journalArticle

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abstract = "Salmonella and Cronobacter are two bacteria of concern in powdered food ingredients with low water activity, due to their ability to remain viable for long periods of time. There is great interest in studying the survival of these bacteria in powdered foods, but discrepancies have been reported between broth-grown and lawn-grown bacterial cells and their thermal resistance and desiccation tolerance once inoculated onto powdered foods. The purpose of this study was to evaluate three different powdered food inoculation methods, two broth-grown and one lawn-grown. To evaluate these methods on three types of powdered food matrices, Salmonella enterica serovar Typhimurium LT2 (ATCC 700720), Salmonella surrogate Enterococcus faecium (NRRL B-2354), and Cronobacter sakazakii (ATCC 29544) were inoculated onto nonfat dry milk powder, organic soy flour, and all-purpose flour using one of the three previously developed inoculation methods. In the first broth-grown method, labeled broth-grown pelletized inoculation, a bacterial cell pellet was added to powdered foods directly and mixed with a sterile wooden stick. The second broth-grown method, labeled broth-grown spray inoculation, used a chromatography reagent sprayer to spray the bacterial cell suspension onto the powdered foods. The third inoculation method, lawn-grown liquid inoculation, made use of a spot inoculation and a stomacher to incorporate each bacterium into the powdered foods. Results indicated that the method of inoculation of each powder impacted repeatability and bacteria survivability postequilibration (4 to 6 days). Brothgrown spray inoculation, regardless of the powder and bacterium, resulted in the highest log reduction, with an average ~1-log CFU/g reduction following equilibration. Broth-grown pelletized inoculation resulted in the second-highest log reduction (~0.79 log CFU/g), and finally, lawn-grown liquid inoculation was the most stable inoculation method of the three, with ~0.52- log CFU/g reduction. Overall, the results from this inoculation study demonstrate that inoculation methodologies impact the desiccation tolerance and homogeneity of C. sakazakii, E. faecium, and Salmonella Typhimurium LT2.",
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