The most probable number (MPN) technique is extensively used in food microbiology. However, because statistics involved often are cumbersome and it is difficult to obtain some of the widely scattered literature, many individuals are not able to delve into the subject to gain a thorough understanding of the method. To overcome these inherent difficulties, this review and discussion was prepared as an introduction and aid in presenting the MPN method to students and individuals working in food microbiology.
Ninety lamb carcasses were evaluated for shrink loss, microbial growth and temperature reduction following treatment with: (1) an edible calcium alginate coating, Flavor-Tex Q; (2) plastic wrap; or, (3) no treatment (control). Lambs (n = 30) were slaughtered on three consecutive days with 10 carcasses/day being randomly assigned to each treatment. Carcasses receiving the edible coating were significantly (P < 0.05) lqwer in 24-hr shrinkage loss (1.55%) than the controls (2.77%); however, those in plastic wrap had the least amount of shrinkage (1.20%), and maintained this advantage through 7 days postmortem. Total surface microbial counts from the sirloin area indicated a significant (P < 0.05) reduction at day 5 and 7 for the alginate coated carcasses, with the plastic wrap carcasses having the highest counts on all days. Internal leg temperature reduction (chilling) was essentially uniform at the end of a 24-hr chill at 2°C regardless of treatment. No significant differences were observed between treatments for cooking loss, flavor, juiciness, off-odor or overall acceptability.
Coliphages were recovered from 18 of 18 fresh chicken and pork sausage samples as well as from 2 of 6 processed delicatessen meat samples employing a rapid technique using EC medium as both an eluent and as a modified phage assay plating medium. Coliphage recoveries ranged from approximately 3.3 to 4.4 log10, 1.2 to 3.5 log10 and zero to 2.7 log10 plaque forming units per 100 g in fresh chicken, fresh pork sausage and roast turkey breast, respectively. High coliphage levels generally reflected high fecal coliform counts, particularly for fresh meat samples. These data indicate that coliphages can be readily enumerated in foods within 16 h.
Effects of a calcium alginate coating on retail beef pieces and steaks were studied. Microbiological analyses were performed on beef pieces following treatments with: (1) a calcium alginate coating; (2) a 200 ppm HOC1 solution; (3) a combination of 1 and 2; (4) a coliform inoculation and/or (5) no treatment (control). Each sample was wrapped in a polyvinyl chloride (PVC) film and stored at 5°C for up to 7 days. The rate of microbial growth for total and coliform counts on the meat was not significantly different with coated and uncoated meat samples. The HOC1 treated meat had significantly lower total microbial counts and coliform populations when compared to either the calcium alginate or the HOCl-calcium alginate treated meat. Acceptance of the calcium al&ate film involved retail display and organoleptic evaluations of 40 2.54 cm thick beef steaks. Steaks that received the calcium alginate coating were significantly lower in shrinkage loss, drip and degree of off-odor detected through 96 hr storage when compared to the uncoated steaks. The coating significantly prolonged muscle color through 96 hr storage. No significant differences were observed between treatments for appearance, surface discoloration, flavor, juiciness, tenderness, overall acceptability or cooking loss.
The distribution of coliphages in various foods and the relationship between the incidences of coliphages and bacterial indicators were investigated. A total of 120 food samples comprising twelve products and including fresh meats, shellfish, vegetables and processed meats, were analyzed for indigenous coliphages using Escherichia coli hosts C, C-3000 and B. Bacterial analyses included enumeration of E. coli, fecal coliforms and coliforms, as well as aerobic plate counts and Salmonella analyses. Coliphages were detected (≥10 PFU/100 g) in 56% of samples and eleven of twelve products. Coliphages, E. coli, fecal coliforms and coliforms were recovered at a level of at least 30 organisms per 100 g in 43, 43, 68 and 81% of samples, with overall mean recoveries of 13, 19, 93 and 4300 organisms/100 g, respectively. Highest and lowest recoveries of coliphages and E. coli were from fresh meats and vacuum-packaged processed meats, respectively. Significant nonparametric correlations between coliphages, E. coli, fecal coliforms and coliforms were found among all food samples.
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