Milk Quality Tests

The Resazurin Test

The Resazurin Test is conducted similar to the Methylene Blue reduction test with the judgement of quality based either on the colour produced after a stated period of incubation or on the time required to reduce the dye to given end-point.

Prepare Resazurin solution by dissolving one Resazurin tablet in 200ml of hot distilled water, place 1ml of dye solution in a sterile test tube then add 10ml of sample. Stopper the tube, place in incubator and when temp reaches 36deg C invert to mix milk and dye. Incubate at 36deg C. Tubes are examined and classified at the end of an hour in the “one-hour test”

Products required from LABTEK Services:

  • RZN-100 Resazurin Tablets (100units
  • RT510100 Reductase 5/10ml Tubes (100units) RTS010190 Stoppers Rubber Red Solid (pk of 10)

Methylene Blue Reduction Test

The Methylene Blue reduction test is based on de-colorization of a dye due to milk quality. The removal of oxygen from milk and the formation of reducing substances during bacterial metabolism causes the colour to disappear. The greater number of bacteria present the faster the dye color will disappear, thus the time of reduction is an indication of the number of organisms in the milk.

Methylene Blue Procedure:

  1. Sterilize all glassware and rubber stoppers either in autoclave or in boiling water.
  2. Boil 200ml of distilled water in a light resistant (amber) stoppered flask and then add one methylene blue tablet, tablet should be completely dissolved and solution cooled before use. Fresh Solution should be prepared weekly.
  3. Add 1ml of Methylene Blue solution into a test tube and add 10ml of Milk and stopper the tube.
  4. Place tubes immediately in waterbath or store in refrigerator for more convenient time of incubation, bring samples to 35deg C within 10mins, when temperature reaches 36Deg C slowly invert tube a few times. Record this as the beginning of the incubation period, cover to keep out of light.
  5. Check samples for de-colorisation after 30mins, make subsequent readings at hourly intervals thereafter.

Products required from LABTEK Services Ltd:

  • MB100 Methylene Blue Tablets (100units)
  • RT510100 Reductase Tubes 5/10ml (100units) RTS010190 Stopper, Rubber, Red Solid (pk of 10)

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