Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2005
Publication Date: 10/1/2005
Citation: Musgrove, M.T., Jones, D.R., Northcutt, J.K., Harrison, M., Cox Jr, N.A. 2005. Shell rinse and shell crush methods for the recovery of aerobic microorganisms and enterobacteriaceae from table eggs. Journal of Food Protection. 68(10):2144-2148.
Interpretive Summary: There are many types of methods available for the recovery of microorganisms from the shells and membranes of eggs. It was theorized that the stage of commercial processing and the target population may influence which recovery method is best. Eggs were collected at twelve different points along the processing chain and sampled by two methodologies: a shell rinse and a shell crush methods. The numbers and presence of aerobic microorganisms and Enterobacteriaceae were determined from samples collected by both methods. For aerobic microorganisms, which are plentiful on eggshells, the methods were equal in how often they recovered this population. However, a greater number of aerobic cells were recovered by rinsing than by crushing, particularly from unwashed eggs. Enterobacteriaceae were recovered most often from eggshells by rinsing for unwashed eggs but more often by crushing shells for washed eggs. This information will assist researchers and quality control personnel in choosing the most sensitive method for analyzing safety and quality of shell eggs. Ultimately, this will allow us to obtain the best information whether conducting commercial surveys or laboratory research.
Technical Abstract: Recovery of bacteria from shell eggs is important for evaluating the efficacy of processing as well as the quality and safety of the final product. Shell rinse (SR) techniques are easy to perform and widely used. An alternative sampling method involves crushing and rubbing the shell (CR). In order to determine the most appropriate method for shell eggs, 358 shell eggs were collected from a commercial egg processor and sampled by SR and CR techniques. Total aerobic mesophiles and Enterobacteriaceae were enumerated on plate count and violet red bile glucose agar plates, respectively. Unwashed (PREP), in-process (INPR), and clean eggs (POST) were evaluated in the study. Aerobic microorganism prevalence for eggshells sampled was similar for both methods (~100%) but log CFU/ ml were higher from SR than CR samples (3.2 and 2.2, respectively). Average Enterobacteriaceae recovery was similar for both methods (45% SR v. 40% CR) when all eggs were considered together. This population was detected more often by SR when PREP eggs were sampled (90% SR v. 56% CR), equally by SR and CR for INPR eggs (30% SR v. 29.3% CR) but more often by CR for POST eggs (10% SR v. 36% CR). SR was easier to perform and recovered larger numbers of aerobic organisms, particularly for PREP eggs. However, CR was more efficient for recovery of Enterobacteriaceae from POST eggs. Stage of shell egg processing may be an important consideration when choosing egg sampling methodology. Key words: shell eggs, methodology, rinse, Enterobacteriaceae, aerobic microorganisms