Microflora of raw milk, sources of milk contamination and their control.

microorganisms present in raw milk and the sources of milk contamination along with its control.

1. Microflora of raw milk. Sources of milk contamination and their control. SUBMITTED TO- SUMBITTED BY- Dr. Paras Porwal Shaista Khan Assistant Professor MSc. MB. 3 rd Semester. AIB. A07199319007 .

2. Introduction- Milk is a white nutrient- rich liquid produce by mammary glands of mammals. Primary source of nut- rition for young ones. Around 6 billion people consumed milk products , globally.

3. Properties of Milk - White emulsion or colloid of butter fat globules. Fat globules and small casein micelles imparts opacity. Yellow-orange carotene provide creamy yellow colour. Contains 30-35% protein per litre of milk, 80% of which is arranged in casein micelles. Oligosaccharides, vitamins ( A, B6, B12, C,D, K), minerals (calcium, Magnesium, etc.) are also present.

4. MICROORGANISMS IN RAW MILK -

5. Milk is sterile at secretion in the udder but it gets contaminated by several bacteria as it leaves the udder. Further the number of microflora in milk can be increase during milking, handling, storage and other pre-processing activities. Supports the growth of several bacteria including the pathogenic bacteria.

6. Alkali-forming bacteria – Aerobic , spore forming bacilli. Renders the milk alkaline. Eg- Alkaligenes spp. Achromobacter. Proteolytic bacteria – Produces proteolytic enzymes, hence causes bitterness and putrefaction. Eg- Bcillus subtilis, Proteus vulgaris, Pseudomonas, Staphylococcus micrococci, etc.

7. Gas-forming bacteria- Produces acid and gas, resulting in the spoilage of milk. Eg- Coliform bacteria, Cl. Butyricum, etc. Acid-forming bacteria – Ferment lactose, forms the lactic acid and leads to the formation of curd. Eg- Streptococcus lactis, Str. Faecalis lactobacilli, Lactoacid bacteria, etc. Presence of inert bacteria shows no visible change.

8. Leuconostoc bacteria- Facultative anaerobes coliform bacteria, with an optimum growth at 37 degree celsius. Can be associated with the presence of milk but not themselves are pathogens. Can cause spoilage of milk as they produce gas and acid resulting in the fermentation of milk. Killed by HTST method. Eg- Escherichia coli.

9. Pathogenic microroganisms in milk - There are some pathogenic bacteria still of concern in raw milk :- Yersinia enterocolitica. Bacillus cereus. Salmonella spp. Campylobacter jejuni. Listeria monocytogenes. E. coli 0157:H7.

10. Moulds- Species of A spergillus, Penicillium, and Fusarium can grow in milk and its products. On favourable conditions, these moulds can produce mycotoxins which can lead to a health hazard.

11. SOURCES OF MILK CONTAMINATION AND THEIR CONTROL -

12. Sources of Contamination - From the farm- During the process of milking, the milk is contaminated by the surrounding areas. Bacteria normally present in soil, manure, and water may enter from this source. The other two most important sources of contamination are milk-contact surfaces and dairy milk utensils.

13. Contd. These includes milking machines and milk pail. The bacteria from these sources involove psychrotrophic (gram negative rods), thermodurics (eg- Micrococcus, Streptococcus, Clostridium, etc. ), Coliform bacteria. Other sources of contamination – Hands or arms of the dairy workers or milker. The air of the milk parlour or the barn. The flies, if present any.

14. 2) At the manufacturing level – After the farm, the other possible contamination may occur via transfer pipes, sampling utensils, transfer trucks, and the equipments use for the processing. Tank pumps, pipelines,vats,valves, and separators are the major possible sources of conatmination. The level of contamination is depend on the sanitizing and cleaning methods.

15. Control method- Animal Cleanliness All animals should be kept clean. All lying areas should be of sufficient size and should be kept clean and dry. Passageways and access routes should be free from accumulations of dung and slurry. Fields, tracks and gateways should be well maintained and kept free from accumulations of dung, slurry and mud .

16. Milking Practices Milk from each animal must be examined for physical/chemical/organoleptic abnormalities and where abnormal milk is detected this milk must be rejected. Teats, udders and adjacent parts must be clean before milking. Hands, contact surfaces and milking equipment must be kept clean at all times. Milking Equipment Milk contact surfaces must be appropriately cleaned and disinfected immediately after each milking. All equipment must be kept clean and in good condition.

17. Milk Storage and Cooling Milk must be protected from contamination during transfer and storage. Milk must be cooled quickly to minimise bacteria multiplication. Bulk tanks must be cleaned and disinfected after each milk collection and kept in good condition . “ these control lies in the guidelines of GMP and HACCP method of food safety.” Where GMP stand for Good Manufacturing Process and HACCP stand for Hazard Analysis and Critical Control Point.

18. Preservation methods - Asepsis . Prevention as far as is practical of the contamination of milk is important in its preservation. 2. Removal of microorganisms . After microbes have entered milk, it is difficult to remove them effectively. So, the process of centrifugation, as in clarifying or separating, will remove microbes from milk. Use of heat (pasteurization and Ultra-pasteurization ). Pasteurization temp- 72 degree celsius for 15 seconds. Ultra-pasteurization temp- 130 degree celsius for 1 sec. or more.

19. Contd.. 4. Steam Under pressure. Evaporated milk is canned and then heat-processed by steam under pressure. The forewarming of milk at 93-100 degree celsius before evaporation kills even resistant bacterial spores. 5. Use of Low temperature (freezing, refrigerated storage). Refrigerated storage- raw milk for pasteurization cooled at 10 degree celsius or less within 2 hrs after being drawn and kept that cold until processed. Freezing- pasteurized milk has been frozen at about -28 to -29 degree celsius and shipped. 6. Drying (condensed products and dry products). 7. Use of preservatives (sugar).

20. Thank you