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Procedure

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Italy

Known as an Italian recipe, with similar versions prepared across other nations.

Ingredients 3 ingredients

  1. Milk
  2. Casserole
  3. 100 ml water
Contains Milk Read from the ingredients, not verified. Check labels.

Method

  1. Pipet graded volumes (0.60, 0.55, 0.50, 0.45, 0.41, 0.38, 0.34, 0.31, 0.28, 0.26 ml) of the 50 unit per ml sample and standard solutions into rows of 10 dry 6-inches x 5/8-inch bacteriological test-tubes.
  2. Add 4.6 ml of the inoculated milk to each by means of an automatic pipetting device.
  3. The addition of inoculated milk is made in turn across each row of tubes containing the same nominal concentration, not along each row of ten tubes.
  4. Place the tubes in a water-bath at 30° for 15 min, then cool in an ice water bath while adding 1 ml resazurin solution to each.
  5. The addition is made with an automatic pipetting device, in the same order used for the addition of inoculated milk.
  6. Thoroughly mix the contents of the tubes by shaking.
  7. Continue incubation at 30° in a water-bath for a further 3-5 min.
  8. Examine the tubes under fluorescent light in a black matt-finish cabinet.
  9. The sample tube of the highest concentration which shows the first clear difference in colour (i.e.
  10. has changed from blue to mauve) is compared with tubes of the standard row to find the nearest in colour.
  11. Make further matches at the next two lower concentrations of the sample and standard.
  12. Interpolation of matches may be made at half dilution steps.
  13. As the standard tubes contain known amounts of nisin, calculate the concentration of nisin in the sample solution.
  14. Obtain three readings of the solution and average them.
  15. Calculate the activity in terms of IU per gram of preparation.
  16. Determination of sodium chloride Accurately weigh about 100 mg of sample, and transfer to a porcelain casserole.
  17. Add 100 ml water, 2 ml 2% dextrin soln, and 1 ml 0.1% dichlorofluoroscein soln.
  18. Mix, and titrate with 0.1 N silver nitrate soln until the silver chloride flocculates and the mixture acquires a faint pink colour.
  19. Sodium chloride, % (w/w) = where: V is the volume of silver nitrate solution consumed (ml), N is the normality of the silver nitrate solution, 58.5 is the formula weight of sodium chloride, and W is the weight of the sample (mg).

Plating

Cookware for this recipe

  • Casserole pot