Several methods for estimation of the potential shelf-life of pasteurized fluid milk products were evaluated for their efficacy in this investigation. These methods were evaluated and compared to sensory, biochemical and bacteriological indices through a series of experiments conducted on different brands of commercially pasteurized fluid milk. The methods evaluated included: Standard Plate Count (SPC), Psychrotrophic Bacteria Count (PBC), Modified Psychrotrophic Bacteria Count (MPBC), the Moseley keeping quality test (MKQT), Parmelee tube test (PTT), tetrazolium salt-resazurin test (TRT), modified Parmelee tube test (MPTT), and p-iodonitrotetrazolium violet-phenazine methosulfate test (INT-PMS). Several different conditions of preliminary incubation (PI) were attempted in an effort to accelerate outgrowth of psychrotrophic bacteria and hence obtain sufficient numbers and metabolic activity to reduce the redox potential indicator dye. Correlation coefficients (r) and chi-square (χ²) values were obtained in an attempt to detect significant relationship between the parameters studied and the potential shelf-life of the product. Results suggested that the PTT, TRT and MPTT tests were not reliable predictors of the potential shelf-life of pasteurized milk (r values between -0.445 and 0.734, non-significant P>0.05). The INT-PMS Test at 21°C for 20 minutes following PI at 21°C for 25 hours provided the best estimate of the potential shelf-life of pasteurized whole milk (r= -0.840). This method shows some potential as a method for determining post-pasteurization contamination: it was accurate (92.3%), rapid ( <26 hours), simple, inexpensive (4.54 to 9.64 cents/sample), and sensitive (it was able to detect less than 1 PBC/ml and less than 5.0 x 10¹ total CFU/ml in fresh milk if bacteria were able to reach 1 PBC/ml and 1.0 x 10³ total CFU/ml during PI). However its accuracy could be significantly affected by the intensity of the pasteurization heat treatment given to the milk due to possible denaturation of the whey proteins and release of heat activated reducing substances (-SH groups). / Graduation date: 1987

No description available.

Thesis (MMedVet. (Production Animal and Community Health, Veterinary Science))--University of Pretoria, 2000. / Also available in print format.

Afhandling--Kgl. Veterinaer- og Landbohøjskole, Copenhagen. / Summaries in Danish and German. Includes bibliographies.

Inaug.-diss.-Bern. / "Literaturverzeichnis": p. [61]-64.

No description available.

Thesis(M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.

No description available.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1983. / Typescript. Vita. Includes bibliographical references.

Selected public health criteria of pasteurised milk available to the consumer from milk -shops in a selected area of Pretoria compared with a national distributor's milk were evaluated. Pasteurised milk samples were obtained from five randomly selected milk-shops in the northwestern part of Pretoria over a six-week period from June to August 1998. Milk from a wellknown national distributor was also obtained from three supermarkets in the same area during the same time period to act as the control milk. Mean total aerobic bacterial counts, coliform counts and psychrotrophic bacterial counts were determined. The presence of Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Salmonella species, staphylococcal enterotoxins, inhibitory substances, alkaline phosphatase and somatic cells in milk were also determined. Of the 135 milk samples purchased from milk-shops, 87% were not fit for human consumption on the basis of the minimum standards prescribed in the Foodstuffs, Cosmetics and Disinfectants Act (Act 54 of 1972). In contrast, 100% of the 79 control milk samples passed all the safety criteria laid down in the Act. x Milk-shop milk quality varied between milk-shops and between sampling days. All milk-shop milk was sold as having been pasteurised, yet 38.5% of milk samples purchased failed the alkaline phosphatase test, indicating that they had not been pasteurised correctly or were contaminated with raw milk. The total aerobic plate counts were generally high for all milkshop milk samples ranging from 1.0 x 102 to 2.7 X 107 CFU/mQ with a median value of 41000 CFU/mQ, whereas for the control milk it ranged from 7.0 x 102 to 8.7 X 103 CFU/mQ, with a median value of 2 200 CFU/mQ. Coliform counts varied from 0 to 3.4 X 104 per mQ in milk-shop milk, with 68% of samples having counts lower than 20 coliforms/mQ, which is the maximum number allowed when the Petrifilm method of counting is used. Coliforms could not be detected in 1 mQ of control milk samples. E. coli was detected in 1 mQ of 17% of milkshop milk, 95% of which originated from milk which was alkaline phosphatase positive. Salmonella spp. could not be detected in 1 mQ in any of the E. coli-positive milk tested. Psychrotrophic bacterial counts done after pre-incubation of milk-shop milk were extremely high, and ranged from 3 x lOS to 2.2 X 108 CFU/mQ, with a median value of 2.4 x 107 CFU/mQ. In Europe the psychrotrophic count may not be greater than 100 000 CFU/mQ. None of the milk-shop milk passed this European standard, whereas 98.7% of the milk obtained from the national distributor fell within the prescribed parameters. S. aureus was isolated from 54 (40%) milk-shop milk samples, and four (7.8%) of 51 isolates tested produced staphylococcal enterotoxins A (SEA), B (SEB), D (SED) or a combination. Control milk did not contain any S. aureus and 15 milk samples tested for the enterotoxin gave a negative result. All control milk was negative for inhibitory substances, but these were detected in 54.1 % of milk-shop milk. Somatic cell counts varied between 1.2 x 104 and 1.6 x 106 cells/mQ in the milk-shop milk, with a median count of 4.2 x 105 cells/mt Only 18.7% of samples had counts above the legal limit of 500 000 cells/mQ. The national distributor's milk always had counts less than 150 000 cells/mQ. xi The results showed that milk-shop milk differed significantly (p < 0.05) from the national distributor's milk, and that the quality of milk purchased from milk-shop outlets was generally of a poor bacteriological quality. The presence of inhibitory substances, and the isolation ofE. coli and S. aureus (some of which were able to produce enterotoxins) indicated potentially unsafe milk and posed a serious public health risk to consumers. / Dissertation (MMed Vet (Hyg))--University of Pretoria, 2000. / Production Animal Studies / unrestricted