MICROBIAL QUALITY OF MILK AVAILABLE IN KATHMANDU VALLEY

Journal of Nepal Medical Association 2004; 43: 137-140 ORIGINAL ARTICLE MICROBIAL QUALITY OF MILK AVAILABLE IN KATHMANDU VALLEY * * ** Arjyal C , Dahal B N , Khadka B ABSTRACT With an objective to find microbial quality of the market milk available in Kathmandu valley, this study was conducted in the Microbiology Laboratory, Himalayan College of Agriculture Science and Technology (HICAST). Different milk brands were collected from different outlets in the valley and analyzed for microbial quality. The samples were cultured using the standard microbiological techniques. Almost all the samples showed the presence of bacterial growth including coliform bacteria. The bacterial isolates were of 7 different genera. E. coli was the most frequently isolated organism (92%) followed by coagulase negative Staphylococci (CONS) (24%). Other organisms isolated were Bacillus species, Staphylococcus aureus, Streptococcus species, Salmonella species, Shigella species. The culture results were similar to direct microscopic count results and showed that bacterial contamination in some of the samples was too numerous to be counted. Thus, it was concluded that the market milk available in Kathmandu is contaminated with various types of microorganisms and does not meet the required standard. The dairy industries should work seriously to maintain the standards of their products. Key Words: Microbiology, Contamination, Milk, Quality, Coliform. INTRODUCTION Milk is one of the most complete single foods available in nature for health and promotion of growth. It supplies the body building proteins, bone-forming minerals and healthgiving vitamins and furnishes energy giving lactose and milk fat. Milk contains the above nutrients in an easily digestible and assimilable form. All of these properties make milk an important and ideal food.1 Since milk is a good medium for practically all microorganisms, there is a risk that pathogenic bacteria will develop in milk and thus spread through milk. The microorganisms often encountered in milk are of various types including spoilage bacteria like Proteus spp., Serratia spp., Pseudomonas fluorescens, Brevibacterium linens; spore forming bacteria like Bacillus spp., Clostridium spp.; coliform bacteria like Escherichia coli, Enterobacter aerogenes etc. In addition to these, many other pathogenic types like Streptococci, tubercle bacilli, Brucella abortus, Bacillus anthracis, Corynebactrium diphtheriae, Salmonella spp., Shigella spp., Staphyloccocci, Clostridium botulinum are found in milk. 2 Human infections may be caused by the ingestion of animal milk which contains microorganisms derived either from the animal, e.g. by contamination with its feces, or from the environment or from milk handlers such as dairy workers.3 The diseases transmitted by milk include tuberculosis, typhoid fever, scarlet fever, septic sore throat, undulant fever, gastroenteritis, diphtheria.4 Other diseases include dysentery, food poisoning, anthrax and paratyphoid fever. 2 The annual bulletin (2001/2002) published by Department of Food Technology and Quality Control has shown that the milk available in Kathmandu valley is highly contaminated by coliform and other group of microorganisms.5 * Integrated Bioscientific Research Group (BIOINT), Kupondol, Lalitpur, Nepal. ** Himalayan College of Agriculture Science and Technology (HICAST), Gatthaghar, Bhaktapur, Nepal. Address for correspondence : Charu Arjyal Integrated Bioscientific Research Group (BIOINT), Kupondol, Lalitpur, Nepal. Email: JNMA, May - June, 2004, 43 Arjyal et al. Microbial Quality of Milk Available in Kathmandu Valley This trend has been persisting since many years and there seems to be no improvement in the quality of the milk. This study was undertaken with a view to find out the microbial quality and also the microbial load of the major milk brands available in Kathmandu valley. It was felt necessary that everybody involved with milk and dairy products should be familiar with the nature and characteristics of pathogenic bacteria so that they can take the appropriate measures to combat them in the daily production and use. 60000 50000 40000 Bacterial load per ml 30000 20000 10000 0 A B C D F G H I MATERIALS AND METHODS 138 J K L M N Fig. 1 : Bacterial load per milliliter in milk by direct microscopic count (DMC) method bacteria per ml milk A total of 14 different milk brands (A,B,C…,N) available at the major outlets in Kathmandu valley were analyzed to determine the microbial load and the quality of the milk. For each brand, 10 samples were analyzed for the reliability of the test. whereas the maximum load was found in sample E in which the number of bacteria was too numerous to be counted (TNTC) and could not be shown in the figure. Among the countable ones, sample K and M had maximum load i.e. 56593 bacteria per ml milk. The results are expressed in figure 1. The study was carried out following the standard microbiological technique as listed below. After collection of the sample, they were transported to the laboratory within a period of 30 minutes to 1 hour and processed immediately. The microbiological analysis included three major tasks Direct Microscopic Count (DMC), Dye Reduction Test and Total Plate Count (TPC). DMC was performed by the conventional Breed count method and the total number of organisms per ml of milk was determined. Dye reduction test was performed by Methylene Blue Reduction Time (MBRT) test. The time required for the reduction of methylene blue, a redox dye, by the milk sample was determined. The quality of the milk was then interpreted using the standard chart.6 Total Plate Count was performed following the pour plate method. The total microbial load was found using the all purpose nutrient agar (NA) and the total coliform count per ml of the sample using the selective media for coliforms, Violet Red Bile Agar (VRBA). The different types of colonies on these two agar media were then sub-cultured to obtain pure culture of these organisms. The pure culture thus obtained was used for different biochemical tests and the identification of the bacteria was done according to their colonial, morphological and biochemical characteristics. RESULT AND DISCUSSION The result of direct microscopic count (DMC) showed that the sample N had the minimum bacterial load i.e. 3961 Good 57% Bad 29% Very bad 7% Fair 7% Fig. 2 : Quality of milk samples as shown by methylene blue reduction time (MBRT) test The results of methylene blue reduction time (MBRT) test as shown in figure 2 showed that eight of the samples were of good quality, one of fair, four of bad quality and one of very bad quality. The result of this test is based on the approximate estimation of the quality of the milk using a standard value chart.6 Methylene Blue Reduction time test like other dye reduction tests is usually done in dairy industry for assessing the overall microbial quality of raw milk.7 This study was c (...truncated)