A comparison of selected public health criteria in milk from milk-shops and from a national distributor

Abstract

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.