A microbial challenge test of a commercially available non-shelf-stable formulation fruit pie
LE3 .A278 1998
Bachelor of Science
To determine the safety of a food product, some food companies and government agencies conduct a microbial challenge test (MCT). This study conducted 3 repetitions of a MCT on a commercially available non-shelf-stable formulation fruit pie, using 2 strains each of Listeria monocytogenes, Staphylococcus aureus, Campylobacter jejuni, and Salmonella spp. Each strain was tested at 3 inoculum levels -1D2cfu/g, 104cfu/g, and 106cfu/g. It was determined, using ANOVA, that pathogen, strain, and inoculum level interactions had significant effects on the mean population counts and growth rates over an 8 day period. It was determined that pathogen type, significantly (F pr<0.001) affected the average microbial population(log10 cfu/g of pie filling), as did the initial inoculum level (F pr<0.001). Pathogen.strain interactions revealed significant differences between the mean population counts of the 2 strains of Listeria monocytogenes, which behaved quite differently from each other on both the non-selective Tryptic Soy Agar (TSYA) and the selective Oxford agar. Staphylococcus aureus behaved differently in relation to the other 2 pathogens, but the 2 strains of S. aureus behaved similarly to each other. This suggests, as did the pathogen.strain.inoculum level interaction, that not only is pathogen type important in a MCT, but so too is strain and inoculum level. Salmonella.spp. showed substanitially lower mean population counts when measured on both TYSA and Brilliant Green Agar compared to the other 2 pathogens. In combination, these results are evidence of the importance of each of the factors and factor x factor interactions as influential conditions that can have significant effects on the outcome of the MCT, and should be considered prior to the MCT being conducted.
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