SOP: Determination of Total, Fixed and Volatile Acidity in Pickles and Chutneys

GIFSQ — Global Institute for Food Safety & Quality

Principle

The total acidity of the pickle or chutney is found by titration of a weighed portion of the composite sample. A second portion is evaporated with water to drive off the volatile acids; the acidity remaining is the fixed acidity, and the difference between total and fixed acidity is the volatile acidity. Results are expressed as acetic acid. In sweet pickle containing oil, the oil is first separated from the aqueous extract so it does not interfere.

Apparatus required

• Evaporating dish
• Water bath
• 250-ml separating funnel

Reagents

a. Reagents for total acidity as prescribed for vinegar (0.5 N NaOH, phenolphthalein indicator).

b. Water.

Procedure

For sweet pickle containing oil: weigh 25 g of the composite sample into the sample container, add 150 ml of water, stir vigorously and allow to settle; transfer the supernatant to a 250-ml separating funnel and allow the water and oil layers to separate; drain the aqueous layer back into the sample container; wash the oil phase once or twice with 5 to 10 ml portions of water and transfer the washings to the sample container

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Total acidity: determine the total acidity in 25 g of the composite sample by the procedure prescribed for vinegar

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Fixed acidity: to another 25 g of the sample in an evaporating dish, add about 150 ml of water and evaporate on a water bath; determine the acidity of the residue, which gives the fixed acidity

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Volatile acidity: take the difference between the total acidity and the fixed acidity as the volatile acidity

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Express the results as acetic acid

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Alternatively, instead of evaporating and finding volatile acidity by difference, determine the volatile acids in the sample (with water added, and the oil separated in the case of sweet pickle) by steam distillation as in the case of vinegar

Precautions

• Adopt repeated evaporation or continued distillation where needed to ensure accurate estimation of the volatile acidity.
• Keep the sample portions identical (25 g) for the total and fixed acidity determinations.

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.