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United States Department of Agriculture

Agricultural Research Service


item Narang, Neelam
item Cray Jr, William

Submitted to: Food Protection Trends
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2006
Publication Date: 5/1/2006
Citation: Narang, N., Cray Jr, W.C. 2006. Evaluation of hand mixing of ground beef and poultry specimens as an alternative to stomaching for the detection of salmonella. Food Protection Trends. 26:14-19.

Interpretive Summary: In food testing and regulatory microbiological laboratories, large numbers of food samples are processed daily to determine the presence of specific pathogenic bacteria. An instrument called a Stomacher is routinely used to homogenize foods such as raw ground beef, poultry, and cooked meat samples to detach the bacteria from the food samples. The Stomacher apparatus, however, is relatively expensive, the procedure is time consuming, and there is the possibility of cross-contamination of food samples and the laboratory. The present study was undertaken to compare the effectiveness of hand mixing of samples to pummeling using a Stomacher for detection of Salmonella in artificially contaminated raw ground beef and poultry samples. Food samples seeded with Salmonella at different concentrations were processed for the detection and identification of Salmonella according to the method described in the FSIS (Food Safety and Inspection Service) Microbiological Laboratory Guidebook Chapter 4.02. No notable differences were observed in numbers of recovered bacteria between the two types of treatments in ground beef, chicken, and turkey samples inoculated with different Salmonella isolates. The results suggest that both treatments can be used in laboratory protocols for detection of Salmonella isolates in food. Thus, it may not be necessary for the FSIS and food testing laboratories to process large numbers of samples using a Stomacher apparatus, since simple hand mixing of samples was shown to be equally effective for detaching the target bacteria from food. Hand mixing of samples reduces testing costs, processing time, and the possibility of contamination when large numbers of food samples are processed.

Technical Abstract: A study was conducted to compare hand mixing with pummeling in a Stomacher for preparing raw ground beef and poultry samples for the detection of Salmonella. A total of 800 ground beef samples, and 400 each of ground chicken and turkey, were analyzed. Ten Salmonella isolates were studied in ground beef and five each in ground chicken and turkey. Each package of raw ground meat was divided into eight (25 g each) samples. Six of the samples were inoculated (0.04-0.25 CFU/g) with one of ten Salmonella isolates. Three samples were hand mixed briefly until clumps were dispersed, whereas, the other three were pummeled in a Stomacher for two minutes. The additional two samples were not inoculated and served as controls. The samples were processed for detection and identification of Salmonella according to methods described in the FSIS Microbiological Laboratory Guidebook 4.02. Statistical analyses using the analysis of variance and t-test showed no evidence of a significant (p< 0.05) difference in CFU/ml and MPN/g between the two treatments for any of the ground beef and turkey samples inoculated with Salmonella. In ground chicken samples, there appeared to be no consistent treatment effect across the five isolates studied; when analyzed as a group, there was no evidence of a treatment effect on the detection of Salmonella spp. This study demonstrated that pummeling of food samples with a Stomacher can be substituted with hand mixing to detach bacteria, since all of the ten Salmonella isolates tested could be detected following both treatment methods in the three types of food samples.

Last Modified: 06/21/2017
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