Dairy Microbiology of Fluid Milk

1. Hygenic milk production system; microbial quality of milk produced under organised and unorganised milk sector in India and composition with developed countries.
2. Microbial and non-microbial contaminent their sources entry points and effects. In milk during the various stages of production and processing.
3. Good hygenic practices (GHP) during milk production operation and processing.
4. Microorganisms associated with raw milk is mainly; morphological and biochemical characteristics of important group and their classification. Significance of different group of bacteria i.e., Cyclotrophs, Mesophilic, Thermoduric and Thermophyl.
5. Microbial changes in bulk refrigerated raw milk, impact of various stages like milking, chilling, storage and transportation. On microbial quality of milk with special reference to cyclotrophic organism.
6. Direct and indirect rapid technique for assesment of microbial quality of milk in industries.
7. Role of microorganism in spoilage of milk, souring, curding, protolysis (anerobic breakdown of protein).
8. Abnormal flavours and discolouration.
9. Mustitic milk; processing and public health significant, organism causing mustitis.
10. Study of milk as a vehicle of pathogen, food infection and intoxication of milk. Milk infection caused by milk bond pathogens. Bacillus syrus, S or ES, Bacillus suptilis and many more.
11. Anti - micobial substances immunoglobline, lactophilene and LP System.

Microbiological aspects of Fluid Milk

1. Pasteurisation, boiling, sterilisation, UHT, non - thermal (pulse feed microfiltration), bactofugation, standardistion, thermonisation.
2. Significant of heat resistance and post processing contaminents in fluid milk, with a special reference to proteases and lipase enzymes and their role in spoilage of processed milk.
3. Biophil during processing and their controlled measures, public health aspects of fluid milk:

• Microbial diseases transmitted to fluid milk.
• Milk born diseaases.
• Microbial grading and legal standards of raw and processed milk.

Microorganisms related to Raw Milk

• Cyclophiles: They grow on very low temperature i.e., refrigerated temperature.
• Mesophile: They grow at room temperature. Prevention of mesophiles is through refrigeration or pasteurisation.
• Contamination:

1. Air contamination i.e., air born microorganism. Examples: spores forming organisms, Bacillus.
2. Soil contamination, while milking, through hands of milking man, storage, utensils, etc.
3. Water contamination (Main Contamination), while cleaning udder, cleaning utensils, mixing, etc. Examples: E.coli, Proteases, Enterococcus.
4. Formation of film (milk layer) in processing plant.

• Types of Contamination:

1. Microbial Contamination
2. Non - Microbial Contamination

Microbiology of Raw Milk

• Pasteurisation
• Process
• Number of microoraganism in raw milk

The number and types of microorganism present in the raw milk depend on the nature and extent of the contamination that terms or varies with condition of milk production and subsequent storage container. The microbial count in the raw milk usually vary from less than 1000 per ml to more than 1000000 per ml. The microbial load in the raw milk can be estimated by SPC. The different test which provides estimation by microbial loads are dye reduction type test (MBRT) and Resourary reduction, Presemptive Coliform Test.

Pasteurisation Principle

Temperature is inversalyy proportional to time.

Source of Microorganism in Raw Milk

Air, water, feed, health, storage, milking animal, infected udder, collection center, collection tank, transportation, contamination during process, contamination during or after packaging.

• Abnormal MIlk
• Mustitic Milk

Mustitic milk is the milk fromanimal suffering from udder disease called mustitis. It has higher microbial load and somatic cell count, it also has altered composition and reduced yield. According to IDF mustitis is defined as inflammation of  udder almost always of microbial origin and is the outcome of either of microbial origin and is the outcome of either of local or general infection. Common symptoms are swelling, 'hot red' udder with painful sensation.

Forms of Mustitis based on Symptoms or Extent of disease:

1. Acute or Clinical: This is the form in which macroscopic changes in milk or udder are readily detected by milker or milkman.
2. Sub-acute or sub-clinical: This is the form in which both milk and udder appears to be normal and can be examined only by the various compositional changes and presence of pathogenic bacteria and somatic cells.
3. Chronic: This form of mustitis involves the little compositional changes in milk and complete absence of pain in the udder.

Common forms of mustitis based on Causitive Organism

1. Contagenous Mustitis: Streptococcus agalactic.
2. Coomon Mustitis: mainly due to Streptococcus, Strephylococcus andd E.coli.
3. Summer Mustitis: Mainly caused in the summer season due to organism known as Corynebacterium pyogenes.

Microorganisms causing Mustitic Milk

The types of microorganisms which can cause infection in the udder of milking animals are:

• Bacterial Species

1. Coliforms (E.coli, Anterobacter, Khebsiella, Citrobacter)
2. Steptococcus Species (Streptococcus uberis, Strptococcus faecalis, Steptococcus pyrogenes)
3. Stephylococcus Species (Stephylococcus epidermis, Stephylococcus albus)
4. Psudomonas
5. Micrococcus Species
6. Bacillus (Bacillus cereus, Bacillus subtilis)
7. Clospridiem
8. Brucella abortus
9. Actinomycetes
10. Nocardia
11. Mycoplasma (Mycoplasma bovis)
12. Rickettsia (Coriella burnetti)

• Fungus Species

1. Molds. Example: Astergillus.
2. Yeast. Example: Candida, Cryptococcus.

Somatic Cells present in Mustitic Milk

The animal body cells called somatic cells are normally present in the milk but as their number increases this depicts the cause of mustitic milk. There are two types of somatic cells which are associated with milk:

1. Epithial Cells: Derived from thee outer surface of the decreating tissue of the udder.
2. Lucosides of WBC: Derived from blood and are more adounded than epithilial cells or their fragments.

Compositional changes in Mustitic Milk

1. Constituents with increased concentration: The levels of total whey protein mainly bovin serum, elbumin, eminoglobilin, sodium, chloride and other ions like copper, iron, zinc various enzymes and certain glycoprotein increases significants. pH of milk also increases.
2. Constituents with decreased alityconcentration: The levels of lactose, fat, total casiem some whey protins (beta lactose globline), potassium and other minerals like calcium, magnesium, phosphorus decreases with the mustitis. Mustitic milk generally have lower SNF, fat content, casiem and lactose with higher serum protein, chloride ion and pH.

Significance of Mustitic Milk

1. Milk Yield: The net milk yield and also the productive life of the milking animal are adversly affected due to mustitis.
2. Milk Quality: Quality of milk decreases due to compositional processes. It also hamper quality and leads to poor product stability.
3. Sutability for Fermentation: Mustitic milk is not suitable for fermentation industry.

Tests for Mustitis Milk

Mustitic milk can be detected on the basis of tests used for examination of different causing organisms such as microscopy test.

1. Hotis Test
2. Blood Agar Plating
3. Higer pH
4. Chloride Test
5. Catalase Test

• Chlorine Test: Normal milk has chloride content from 0.08  to 0.18%. Abnormal milk has more of chloride content then 0.18% chloride content of milk can be tested by addition of 0.1435% of silver nitrate solution (5 ml) and 2-3 drops of indicator potassium chromate (10% solution). A yellow colour appearence indicates higher quality of chloride content.
• Catalase Test:; Presence of catalase can be examined by evolution of oxygen on addition of Hydrogen peroxide 3% to milk, 9 ml of milk + 1 ml of Hydrogen peroxide. This indicates presence of mustitic organism organism in milk.

Somatic Cell Count

An increase in somatic cells indicates increase in mustitic organism.

1. Sodium Loreal Surface Test
2. Direct Lucoside Count
3. Resasuring Rennet Test

This test is based upon the distribution in the salt balance and increases in lucosite content in mustitic milk cogulation of milk by rennet is slowedd due to distributed salt balance and lucosite reduce due to lucosite abnormal.

Microbiological Test

1. Microscopic Examination
2. Hotis Test: This test is meant for differentiation of streptococcus agalactiae milk (9.5 ml) is mixed with 0.5% aqueous solution of bromo crysol purple (indicator) and incubated at 37 degree Celcius for 24-74 hours in the culture tube. The appearence of yellow colonies along the walls of test tube or at the bottom of the tube dignosis the positive test for Streptococcus agalactiae, whereas Stphylococcus alorius gives rusty brown colour on the walls of the tube.
3. Blood Agar Test: The mustitic milk sample is plated on the blood agar media.

(a) Observation: Small colonies and humolysis. Organism: Streptococcus agalactiae

(b) Observation: Small zone around the colonies and green discolouration. Organism: Streptococcus dysgalactine

(c) Observation: No reaction. Organism: S. ulberis.

(d) Large colonies than Streptococci a wide zone of clearence around colonies. Organism: Stephylococcus atorius.

Lactoperoxides

Lactoperoxide is present in milk in considerable amount i.e., 30 mg/ml. This enzyme has been found to be identical with LZ fraction of lactinies. The inhibitary action of this enzymes is due to the formation of anti-microbial system (lactoperoxide, thiocynide, hydrogen peroxide) the secreation of thiocynide in the milk is governed by the neutrition of the contributed either by polymorpho nuclear glocosides (PML) or by the hydrogen peroxide reducing udder flora. The LP system system is the bacterioststic for the organism like Streptococcus, Saslmonela, Strephylococcus, Listeria.

Significance of anti-microbial system present in Milk

1. Prevents spoilage of milk.
2. Prevention of new born diseases to human.
3. Help in the processing problem.
4. Help to stabilize composition.
5. Starter culture propagation and prevention.

Microbial quality controlled test for Raw Milk

• 1. Rapid Platform Test
• Organo laptic Test
• Clot on Boiling
• pH
• Titratable Acidity
• Sediment Test
• Alcohol Aliglene Test
• 10 minute Resasuring Reduction Test
• Direct Microscopic Count

2. Microbiological Testing

• Standard Plate Count (SPC)
• Dye Reduction Test (MBRT)
• Coliform Test
• Thermoduric Count (very high temperature 110 degree Celcius)
• Thermophilic Count
• Spore Count
• Protolytic and Lipolytic

3. Test for Abnormal Milk

• Mustitic Milk - pH, chloride content, resasuring rennet test, somatic cell count, hotis test, blood agar test.
• Milk with anti-biotic Residue - different test to be conducted for residual anti-biotic.

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