National University of Singapore
Food Science & Technology
Determination of colour change in Anthocyanins
Materials:
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Grape Juice
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Ribena
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1 M NaOH
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Test-tube
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pH meter
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250 ml Beaker
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Magnetic Stirrer
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Micropipette
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Plastic Dropper
(Top) Demonstration video on effects of pH on the colour changes of anthocyanin.
Procedure:
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Mix 25 ml of the fruit juice and 25 ml of deionized water.
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Determine the pH of the solution.
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Remove 5 to 10 ml of this solution to a test tube.
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Adjust the remaining solution to pH 5.0 with 1 N NaOH.
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Remove 5 to 10 ml of this solution to a test tube.
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Adjust the remaining solution to pH 7.0.
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Remove 5 to 10 ml of the solution to a test tube.
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Adjust the remaining solution to pH 10.0.
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Remove 5 to 10 ml of the solution to a test tube.
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Compare all the samples, especially noting the colour.
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Repeat steps 1 to 10 with other fruit juice.
ATTENTION:
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Students tend to record the pH of the solution before the pH stabilises. Ensure that the pH stabilises before removing the solution.
Colour changes of anthocyanin at different pH. From left to right: original pH of ribena, pH 5, 7 and 10
Due to its ability to change colour at different pH, anthocyanin is sometimes used as a natural pH indicator. Therefore, if you want to conduct a kitchen experiment on the acidity of certain foods in the kitchen, grab some red cabbage and extract its juice and you have for yourself a home-made pH indicator.