Appendix XI N. Bitterness Value

The bitterness value is the reciprocal of the dilution of a compound, a liquid or an extract that still has a bitter taste. It is determined by comparison with quinine hydrochloride, the bitterness value of which is set at 200 000.

A taste panel comprising at least 6 persons is recommended. The mouth must be rinsed with water R before tasting.

To correct for individual differences in tasting bitterness amongst the panel members it is necessary to determine a correction factor for each panel member.

Stock solution Dissolve 0.100 g of quinine hydrochloride R in water R and dilute to 100.0 mL with the same solvent. Dilute 1.0 mL of this solution to 100.0 mL with water R.

Reference solutions Prepare a series of dilutions by placing in a first tube 3.6 mL of the stock solution and increasing the volume by 0.2 mL in each subsequent tube to a total of 5.8 mL; dilute the contents of each tube to 10.0 mL with water R.

Determine as follows the dilution with the lowest concentration that still has a bitter taste. Take 10.0 mL of the weakest solution into the mouth and pass it from side to side over the back of the tongue for 30 s. If the solution is not found to be bitter, spit it out and wait for 1 min. Rinse the mouth with water R. After 10 min, use the next dilution in order of increasing concentration.

Calculate the correction factor k for each panel member from the expression:

Persons who are unable to taste any bitterness when using the reference solution prepared from 5.8 mL of stock solution have to be excluded from the panel.

If necessary, reduce the sample to a powder (710) (2.9.12). To 1.0 g of sample add 100 mL of boiling water R. Heat on a water-bath for 30 min, stirring continuously. Allow to cool and dilute to 100 mL with water R. Shake vigorously and filter, discarding the first 2 mL of the filtrate. The filtrate is labelled C-1 and has a dilution factor (DF) of 100.

If liquids have to be examined, 1 mL of the liquid is diluted with a suitable solvent to 100 mL and designated C-1.

Test solutions:

Starting with dilution C-4 each panel member determines the dilution which still has a bitter taste. This solution is designated D. Note the DF of solution D is Y.

Starting with solution D prepare the following sequence of dilutions:

Determine the number of millilitres of solution D which, when diluted to 10.0 mL with water R, still has a bitter taste (X).

Calculate the bitterness value for each panel member from the expression:

Calculate the bitterness value of the sample to be examined as the average value for all panel members.