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Lab. No. 11. Food Microbiology  Water Milk  Normal flora of milk: Bacteriological Examination of Milk  Enterococcus faecalis  Streptoccus lactus.

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Presentation on theme: "Lab. No. 11. Food Microbiology  Water Milk  Normal flora of milk: Bacteriological Examination of Milk  Enterococcus faecalis  Streptoccus lactus."— Presentation transcript:

1 Lab. No. 11

2 Food Microbiology  Water Milk

3

4  Normal flora of milk: Bacteriological Examination of Milk  Enterococcus faecalis  Streptoccus lactus  Lactobacillus sp.  Candida albicans (yogurt)

5  Pathogenic bacteria may be present in milk: Bacteriological Examination of Milk  E.coli  Streptoccus pyogenes  Mycobacterium tuberculosis  Salmonella sp.  Brucella sp.

6 Bacteriological Examination of Milk  Microscopical Examination of milk: Note the cells of the normal flora  Enterococcus faecalis  Streptoccus lactus  Lactobacillus sp.  Candida albicans (yogurt)

7  Determination of viable bacterial count : Using the pour plate method Using the pour plate method after preparation of 10 fold serial dilution from the milk sample with ringer solution. after preparation of 10 fold serial dilution from the milk sample with ringer solution. Bacteriological Examination of Milk

8 Using 10 fold serial dilution method Viable Bacterial Count 9 ml Saline 1 23 Milk sample 1 ml milk1 ml 1 ml 1/10 1/10 x 1/10 1/100 1/100 x 1/10 1/ ml 1 ml1 ml Melted NA 1 23

9 Results: Viable Bacterial Count Dilution factor 123X X. y 10 x1x1x1x1 X 1.y x2x2x2x2 X 2.y x3x3x3x3 X 3.y 3 No. of colonies per plate Y No. of cells per 1 ml = X 1.y 1 + X 2.y 2 + X 3.y 3 3

10 Permissible number of bacterial flora in pasteurized milk is 5 x 10 4 cfu/ml Permissible number of bacterial flora in pasteurized milk is 5 x 10 4 cfu/ml Permissible number of bacterial flora in long life milk is 10 cfu/ml Permissible number of bacterial flora in long life milk is 10 cfu/ml Results: Viable Bacterial Count

11  Methylene Blue Reduction Test: Bacteriological Examination of Milk Increasing the number of bacterial flora will reduce the colour of methylene blue more rapidly due to increasing consumption of oxygen. Increasing 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. To determine quality of the milk

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 milk Decolorization timeResult 30 min – 2 hrs Poor quality 2 – 6 hrs fair quality 6 – 8 hrs good quality Over 8 hrs excellent 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 كل عام وأنتم بخير With my Best Wishes,,, Manal Abu El-Khair


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