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Fresh Milk Quality Testing Methods

1) Check the specific gravity using the tool Laktodensimeter ditera at a temperature of 27.5 o C. The principle of this test is that solid object which is inserted into a fluid will get upward pressure weighing the displaced liquid volume. Density measured between 20 ° – 30 ° C adjustable at:
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2) The level of fat by Gerber method with the principle of concentrated sulfuric acid and dissolve remodel casein and other proteins, thus causing a loss of form of dispersion of fat. Separation of fat is accelerated by the addition of amyl alcohol will melt the fat with the heat it generated. By centrifugation will cause the fat accumulated on the scale section butirometer

3) The level of non-fat dry matter minimum (BKTL) can use the method of drying. The principle is that a number of milk samples were dried at a constant temperature (constant) until a constant dry weight is reached. Weight after drying is the weight of dry matter.

4) The level of minimum protein using methods kjedahl. The principle is heating the milk sample in concentrated sulfuric acid resulted in the destruction of the protein into its elements. To speed up the destruction process is often added potassium sulphate together with cupri sulfate (as an indicator) so that the group N (organic) will turn into a cluster of ammonium sulfate. Through the addition of sodium hydroxide and heating there was a distillation process in which ammonium sulfate is broken down into ammonia. Further ammonium liberated will be captured by boric acid, whereas the rest of boric acid which does not react with ammonia to be titrated with 0.1 N hydrochloric acid difference in the number of titration blank sample with an equivalent amount of nitrogen.

5) Check the color, smell, taste and viscosity done organoleptic test. The principle is that the milk can change the color, smell, taste and consistency by causes following: 

  • Milk into a bluish color when added to water or reduced fat and become reddish if blood is from a cow suffering from mastitis.
  • The smell of milk will be affected by the milk fat very easily absorb odors from the surroundings.
  • Flavored milk will taste bitter because of the germ forming peptone, milk has a taste of radish caused by coli bacteria, the milk has a taste of soap saponaceae caused by Bacillus lactis, milk has a rancid taste caused by germs sour butter, and milk has a taste rancid by kuman- certain other germs.
  • The viscosity of milk; milk will slimy if contaminated by germs kokki derived from water, food waste or tools milk.

6) Test alcohol; This test is done to check quickly acidity of fresh milk. The principle is the stability of the colloidal properties of milk proteins depends on the water surrounding her veil. This is especially casein. When milk is mixed with alcohol which has the properties of dehydrated then the protein will be coagulated so that the milk will be broken. The higher the degree of acidity of milk is checked, the lower the amount of alcohol with certain concentrations necessary to solve the milk with the same volume. The experiment started positively on the degree of acid 8-90 SH

7) Testing of microbial contamination; Testing of microbial contamination in fresh milk is intended as an indicator of roses sanitation in the production or handling of milk as well as indicators of the health and safety of milk. A wide variety of microbiological test can be carried out, covering microbial quantitative test to determine the quality, qualitative test of pathogenic bacteria to determine the level of security, as well as bacterial test indicator to determine the level of the milk sanitation. Testing of microbial contamination include:

a) Determination of total plate count at 35 o C; The principle is the figure of total plate (Total Plate Count) is intended to indicate the number of microorganisms found in milk with a cup count method. If the surviving microbial cells grown on agar medium, the microbial cells will multiply and form colonies that can be viewed directly by the eye without a microscope.

b) Calculation of Coliform and Escherichia coli; The principle is crystal violet and bile salts in the media would inhibit other Gram-positive bacteria that only grow coliform organisms. During growth, coliform will convert lactose into acids and these changes

will be detected by neutral red indicator will change color to red. Additionally acidic conditions will cause the precipitation of bile acids.
c) Calculation of Staphylococcus aureus with a cup count method; This method is used to calculate the amount of S. aureus is greater than 100 cells per ml of S. aureus / gram sample. The method used is a method of scatter / surface. The principle is to be modified by Staphylococcus Mannitol which grew into an acid and this acid susuana phenol red indicator will change to yellow. Tellurite that there will be a tellurite black.

8) Testing of antibiotic residues qualitative and semi-quantitative screening test. The principle is homogenized milk samples. Tetesi paper disc with samples of milk, and then put the paper discs on the surface of an agar medium that has been mixed with the test bacterial culture and incubated at 37 0 C for 16-18 hours. Milk samples tested positive for residues of antibiotics when the barrier zone is formed around the paper disc.