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International Starch Institute
Science Park Aarhus, Denmark
ISI 14-2e Determination of Acetyl Content

1. Scope The method is applicable to acetylated starch

 

KM
Rev. LT 14 Sep 1999
2. Principle Bound acetyl reacts with strong alkali and excess alkali is titrated

 

3. Apparatus 3.1 Burette
3.2 Conical flask, Erlenmeyer 250 ml with stopper

 

4. Reagents 4.1 Sodium hydroxide 0.1 N
4.2 Sodium hydroxide 0.45 N
4.3 Hydrochloric acid 0.2 N
4.4 Phenolphthalein: 1 g in 1 l ethanol 90%

 

5. Procedure Weigh 5 g of sample to the nearest mg. Transfer to conical flask (3.2) and disperse in 50 ml distilled water. Add a few drops of indicator (4.4) and titrate with (4.1) to permanent pink colour.

Bound acetyl reaction

Add 25.0 ml of NaOH 0.45 N (4.2). Stopper and shake vigorously for hour Use mechanical shaker

Titration 

Flush stopper and neck of flask with a little distilled water and titrate excess alkali with 0.2N HCL to disappearance of pink colour.

Blank

25.0 ml 0.45N NaOH (4.2) is titrated as a blank

 

6. Calculation Calculate acetyl groups by averaging results of two samples with two significant digits:

Acetyl groups % of sample = ((b-s) * N * 0.043 * 100) / w ; where

b = ml 0.2 N HCl used to titrate blank
s = ml 0.2 N HCl used to titrated sample
N = normality of 0.2 N HCL
w = weight of sample in g

Correct eventually to acetyl groups % of sample dry matter

Molecular weight of CH3CO = M = 43
7. Notes Alternative determination of acetyl by enzymatic method ISO 11213

 

8. Reference JECFA

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Keywords: laboratory method determination acetyl group starch