Figure 3. Absorption spectra of cyanidin-3- rhamnoside in buffer solutions at pH values of 0.71-4.02. The concentration of the pigment is 1.6 X 102 g/L.

be removed by addition of potassium hydroxide since the resulting precipitate of potassium hydrogen tartrate can be easily removed by filtration. Purification of the crude extract can be accomplished by passing the extract through an ion-exchange resin bed with the added advantage that the colorant eluate can be fractionated. The first portion of

Commercial specifications are usually confined to tinctorial power, total acidity, %solids, %ash, heavy metals, sulfur dioxide, tannins, and alcohol. The tinctorial strength of grape extracts is often expressed as the ab-sorbance of a 1% solution in a 1-cm cell at 520 nm in citrate buffer at pH 3. The tinctorial power of red cabbage extracts is sometimes expressed as the absorbance of a 10% solution in a 1-cm cell measured in citrate buffer at pH 3 (eg, E 10%, 1 cm = 190).

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