4 Bacteriological Examination of Milk Normal flora of milk:Enterococcus faecalisStreptoccus lactusLactobacillus sp.Candida albicans (yogurt)
5 Bacteriological Examination of Milk Pathogenic bacteria may be present in milk:E.coliStreptoccus pyogenesMycobacterium tuberculosisSalmonella sp.Brucella sp.
6 Bacteriological Examination of Milk Microscopical Examination of milk:Note the cells of the normal floraEnterococcus faecalisStreptoccus lactusLactobacillus sp.Candida albicans (yogurt)
7 Bacteriological Examination of Milk Determination of viable bacterial count :Using the pour plate methodafter preparation of 10 fold serial dilution from the milk sample with ringer solution.
8 Viable Bacterial Count Using 10 fold serial dilution method1 ml milk1 ml1 ml1239 ml SalineMilk sample1/10 x 1/101/1001/100 x 1/101/10001/10Melted NA1 ml1 ml1 ml123
9 Viable Bacterial Count Results:Viable Bacterial CountYDilution factor123XX . y10x1X1.y1102x2X2.y2103x3X3.y3No. of colonies per plateNo. of cells per 1 ml =X1.y1 + X2.y2 + X3.y33
10 Viable Bacterial Count Results:Permissible number of bacterial flora in pasteurized milk is 5 x 104 cfu/mlPermissible number of bacterial flora in long life milk is 10 cfu/ml
11 Bacteriological Examination of Milk Methylene Blue Reduction Test:To determine quality of the milkIncreasing the number of bacterial flora will reduce the colour of methylene blue more rapidly due to increasing consumption of oxygen.i.e: The speed of reduction of methylene blue colour is directly proportional to the number of bacteria present in milk sample.
12 Bacteriological Examination of Milk Methylene Blue Reduction Test:Results:The shorter the decolorization time, the higher the number of bacterial flora present in milk, and the poor quality of milkDecolorization timeResult30 min – 2 hrsPoor quality2 – 6 hrsfair quality6 – 8 hrsgood qualityOver 8 hrsexcellent quality
13 Bacteriological Examination of Milk Test for coliforms:Done by inoculation of MacConkey’s broth with 0.1 ml of milk sample.Examine for the production of acid detected by changing the color of the medium from purple to yellow.
14 Thank youكل عام وأنتم بخيرWith my Best Wishes,,,Manal Abu El-Khair