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International Starch Institute
Science Park Aarhus, Denmark
ISI 12-1e Determination of Acidity

1. Scope The method is applicable to starch milk and hydrolysates


LT 12. Dec. 1966
Rev. LT 16. Dec. 1997
2. Principle Titration with NaOH to pH 8.3.


3. Apparatus 3.1 Burette
3.2 pH meter
3.3 Volumetric flask 50 ml


4. Reagents 4.1 Sodium hydroxide 0.1 N
4.2 Phenolphtalein: 1 g in 1 l ethanol 90%


5. Procedure Fill volumetric flask (3.3) with liquid sample. Transfer to 300 ml conical flask.


Add 1 ml (4.2) and titrate with (4.1) to faint persistent pink  or use pH meter to 8.3
V = ml (4.2). N = normality of (4.2)


6. Calculation Calculate acidity as normality N of sample by averaging results of two samples with one decimal.

N = N V / 50


7. Notes J. Assoc. Off. Anal. Chem. 66 (1983) no. 6, 1395-1399 recommend pH 6.0 as end point, but AOAC limits this method to HFCS.
Ph. EUR 4ed acidity test for starch. Add 10 g sample to 100 ml of alcohol (70 per cent V/V) R previously neutralised to 0.5 ml of phenolphthalein solution R and shake for 1 h. Filter and take 50 ml of the filtrate. Not more than 2.0 ml of 0.1 M sodium hydroxide is required to change the colour of the indicator.
8. Reference AOAC Official Methods of Analysis (15th edition)

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Keywords: laboratory method determination acidity starch hydrolysate