Tariq Masud ( Department of Dairy Technology, National Agricultural Research Centre, Islamabad. )
Abdul Bari ( Department of Biological Sciences, Quaid-e-Azam University, Islamabad. )
A. Amin Shah ( Department of Dairy Technology, National Agricultural Research Centre, Islamabad. )
A total of 244 samples of milk and milk products were collected to assess the staphylococcal counts. Of these, 137 samples were found contaminated with an average staphylococcal count between 9x102/g in dahi to 1 .7x106/g in khoa. Among all the products khoa was heavily contaminated. Measures should therefore be en-forced to control food-borne diseases by the maintenance of high public health standards in foods and meticulous care in their preparation and selling (JPMA 38 , 1988).
Staphylococcal food poisoning is a common illness all over the world and is caused by the ingestion of foods contaminated with the enterotoxins of Staphylococcus aureus. Among foods, milk and milk products are the most common foodstuffs acting as mediators of Staphylococcal intoxication.1-3
In Pakistan milk and milk products such as khoa, kulfi, ice cream, pera, burfi, butter and dahi are consumed in large quantities. Therefore, the present study was done to screen milk and milk products for Staphylococcal counts.
MATERIALS AND METHODS
A total of 244 samples of milk and milk products including khoa, burfi, KulfI, ice cream, pera, butter and dahi were aseptically collected in glass sample bottles from Rawalpindi and Islam. abad markets. The samples were transported to the laboratory and processed within an hour of their collection.
Detennination of Staphylococcal Count
The Staphylococcal count of each sample was carried out according to the procedures prescribed by FAO manual for microbiological food analysis. 4 A ten fold serial dilutions of homogenized sample were made in Ringer’s solution and the diluted samples were poured in sterilized petri-dishes, subsequently these plates were added with Staphylococcus medium No. 110 (oxoid). These plates were incubated at 37°C for 24 to 48 hours. The Staphylococcal concentration in the original sample was estimated from the geomatric mean of count5.
Out of 244 samples examined 137 were found contaminated with Staphylococci while 107 samples did not yield any bacterial growth. There was a large variation in Staphylococcal count among the tested products. The average number of Staphylococci varied from 9x10,2 in dahi to 1 to 1.7x106/g in khoa (Table 1).
Staphylococcal profile of 244 samples is shown in Table II.
The highest Staphylococcal count was recorded in khoa wherein 17 (56.66%) showed a count of 100,0000, followed by 14 (46.66%) milk samples presenting a count upto 1000, next was kulfi 10 (33.33%), ice cream 10 (31.25%), butter 9 (30.00%), Pera 5 (16.66%) and burfi 3(10.00%), harbouring less than i000/g Staphylococci. In case of dahi only four samples (13.33%) yielded staphylococci with a count less than 100/g, whereas 21 dahi samples did not show any evidence of Staphylococcal infection.
The highest frequency of Staphylococcal count was found in khoa (4.8x10~/g) with a very high mean count of 1.7x106. This product is not eaten as such but is stored for sometime at room temperature prior to its use for the preparation of secondary products, moreover certain growth promoting stimulators like serine/glycine, glutamicacid/threonine and proline6 are also present in khoa.
High Staphylococcal count in case of milk could be attributed to hand milking, poor washing of udder and unhygienic utensils used for milk collection and distribution2. Another source is mastitis, which is believed to be present in 50% of the lactating animals7.
Since kulfi, ice cream, and butter are stored at cold temperature, these are expected to be low in microbial counts. Staphylococcal mean count in these products was 4.6x104/g in kulfi and in ice cream 23x104/g. High counts in these frozen products may be due to unhygienic practices and inferior quality of raw ingredients used in their production. The presence of Staphy. lococci in butter may be due to incomplete pasteurization of cream, poor quality of milk, coupled with bad hygiene of the manufacturing unit. Similar frequency of Staphylococci have been reported from USA, Argentina and India with almost similar source of contamination2-3-8
The high Staphylococcal counts observed in pera and burfi in the present study have also been reported earlier9. Dahi samples were least contaminated probably due to its high acidic content. Similar views are expressed by others10
Of the total samples checked ,73% samples had an acceptable Staphylococcal count 102/g whereas 27% samples were not in acceptable range. The International Commission on Microbiological Specifications for Foods (ICMSF) has recommended 102/g Staphylococcal count to be permissible in milk and milk products11 Considering the ICMSF standards 25 khoa, 18 milk, 8 kulfi, 6 pera, 7 ice cream, 2 burfi and one butter sample had non permissible levels. None of the dahi samples attained non.permissible range. Seventeen samples of khoa had a Staphylococcal count of 106/g which could be hazardous to consumers since milk products containing 1 .0x106/g Staphylococcal counts are said to be potentially hazardous12. The presence of coagulase positive Staphylococci in a food Supply is un-desirable, due to rapid multiplication in food and is uncontrolable if proper handling and storage is not observed13.
On the basis of results obtained in this study, it is concluded that milk and milk products available to the consumer in this area have a high number of Staphylococcal count posing a high risk of food-borne disease. The critical time rendering milk and milk products dangerous for human consumption varies from product to product. It is prolonged in case of frozen products which may extend upto weeks. It is hardly more than 6 to 12 hours for products which are stored at room temperature. The critical storage time is also influenced by the type of product, type of ingredients used and its subsequent contamination as well as the storage temperature.
It could be suggested that sooner a milk product is consumed the safer it is. Every added storage hour is likely to double the number of contaminants thus adding more toxins to the product rendering it further dangerous for the consumers. Therefore, it requires a meticulous care during preparation and subsequently handling in order to get a good quality product, safe for human health.
1. Kostic, D., Kostic, S., Maxkovic, M., Nesic, 3. andRandelkovic, M. Microbiology of foods in theterritory covered by the Leskovac Institute ofPublic Health in 1976. Hranai labrana., 1981;22: 137-138.
2. Terayamo, T., Shingaki, M., Igaxashi, H.,Ushioda,H., Takahashi, M., Sakai, S., Yamada, M., Mito,K., Kotegi, T. and Yamaguchi, Y. Incidence of S. aureus in bovine raw milk and some characteristics of the isolates. Annual report of TokyoMetropolitan Res. Lab. Pub. Health, 1980; 31:115.
3. Kahion, S.S. and Grover, N.K. Incidence ofstaphylococci in milk products sampled from Ludhiana. Indian J. Dairy Sci., 1984; 37: 381.
4. FAO Manuals of food quality control No. 4, Microbiological analysis, Rome, 1979.
5. SEAMIC Laboratory diagnosis of bacterial food poisoning and the assessment of sanitary quality of food. 12th Southeast Asian Medical Information Centre Publication Japan, 1978.
6. Varadaraj, M.C. and Nambudripad, V.K.N. Presence of certain growth promoting Factorsin khoa enabling rapid Staphylococcal growth.Indian J. Dairy Sci., 1984; 37:271.
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8. Rivas, M., Cordal de Bobbi, M.E., Palma, M.S.R.and Morn, A.A. ice cream from Industrial sources. Incidence o. Staphylococcus aureus and itsentexotoxigenicity. Revista Argentina de Microbiologia., 1984; 16: 225.
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11. ICMSF. Micro-organism in foods, sampling for microbiological analysis: Principles and specific application. London; University of Toronto Press, 1978.
12. Jay, J.M. Modern food microbiology, 2nd ed.New York, 1978.
13. Donnelly, C.B., Black, L.A. and Lewis, K.H.Occurrence of coagulase-positive Staphylococciin chedder cheese. Appi. Microbiol., 1964; 12:311.