Hygiene evaluation of Milk. Taking of the milk samples. Laboratory tests.
Hygiene evaluation of milk
-good source of proteins, fats, sugars, vitamins and minerals; milks protein is casein (in combination with calcium); contains all essential amino acids; milks carbohydrate is lactose; high in calcium and Vitamin D, NO Vitamin C
Taking samples
-from container: mix the milk 5 min., take 250-300cm³, place it in a clear vessel
-from bottles, cartons, cans: same procedure, when packages are <1000 → each 100. package is taken for sampling; packages >1000 → each 500. Package is taken for sampling
Laboratory tests
-Organoleptic analysis: should be with white or light cream color (homogenously), no sedimentation, agreeable odor, light sweet taste
-Milk density test: done with a "lactometer", density of milk → 1,027-1,034 at 20°C → if temperature is below 20°C: -0,2 for each degree below 20°C +0,2 for each degree above 20°C → example at 17°C: 1,030 – (0,2*3) = 1,024
-Milk acidity determination: by titration of 0,1n NaOH solution → measured in degree of Toerner (T°, 1T° is equal to 1ml NaOH solution needed to neutralize acids in 100ml milk) → normal value fluctuates between 15T°-21T° (should be with slight pink color then) → if >21T° => acidic, may be due to growth of microorganisms in milk
-Pasteurization: heating of milk to a certain temperature over a certain time to destroy any pathogens; several methods: HOLDER, HTST, UHT → to check for the enzyme peroxidase (only present in not pasteurized milk); after adding hydrogen peroxide solution → color change into blue = inadequate pasteurization
-Test for sodium bicarbonate: adding of rosolic acid; color change to yellow/orange→no sodium bicarbonate; color change to raspberry-red→sodium bicarbonate is present
-Microbial content: using direct microbial indices (standard colony count), test for pathogenic microorganisms