Determination of Total Titratable Acidity

Weigh 10-20 g of macerated sample (Sect. 2.3.1) into a tared 250-ml flask and record the exact weight of the sample. Add distilled water to the flask to bring the volume to 100 ml. Colorimetric titration may be used if the sample is not highly coloured or electrometric titration for highly coloured samples. 

Fill a burette (50 ml graduated in 0.1ml) with 0.1 N sodium hydroxide then add three to five drops of phenolphthalein indicator to the sample. While stirring or swirling the titration flask carefully, add alkali from the burette until the colour changes from colourless to a faint pink throughout the solution. The colour should remain after mixing for 30 s. 

Place the electrodes of pH meter in the sample, if the electrode is not covered completely add distilled water. Add 0.1 N sodium hydroxide from the burette while stirring the flask. Continue to add the NaOH until the pH reaches 8.3 on the pH 

For a 10-g sample multiply the number of millilitres of 0.1 N NaOH used in the titration by the appropriate factor for the acid listed below to obtain the percentage of total titratable acid. For a 20-g sample divide the millilitres of 0.1 N NaOH by 2 before multiplying by the acid factor. 

A range of from 03-2.6 malic acid/lOOml juice with an average of 1.6 is normally found for apricot (Mehlenbacher et al. 1983 Visagie 1985). 

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