SOP: Kirschner Value of Fats

GIFSQ — Global Institute for Food Safety & Quality

Principle

The Kirschner value is a measure of the steam-volatile, water-soluble fatty acids forming water-soluble silver salts (butyric acid). After the R.M. value determination, the R.M. titrate is treated with silver sulphate, which precipitates the fatty acids forming water-insoluble silver salts; the remaining filtrate is redistilled and titrated, and the Kirschner value is calculated from the Kirschner and R.M. titres. In recent years, this analysis is not usually done.

Apparatus required

• Standard R.M.-Polenske-Kirschner distillation apparatus
• 9 cm Whatman No. 4 filter paper (dry)
• Dark place (for the silver sulphate treatment)

Reagents

a. 0.05 N barium hydroxide (used in place of 0.1 N NaOH in the R.M. value titration).

b. Finely powdered silver sulphate.

c. Cold CO₂-free distilled water.

d. Dilute H₂SO₄ (25 ml of conc H₂SO₄ made to 1000 ml with water).

e. Pumice powder.

Procedure

Proceed as in the determination of the R.M. value, but titrate 100 ml of the filtrate using 0.05 N barium hydroxide instead of 0.1 N NaOH

↓

After the R.M. value determination, add 0.5 g of finely powdered silver sulphate to the solution; keep in a dark place for 1 hr with intermittent shaking

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Filter through a dry Whatman No. 4 filter paper

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Add 35 ml of cold CO₂-free distilled water, 10 ml of dilute H₂SO₄ and 0.1 g of pumice powder; connect to the distillation apparatus and distil 110 ml in 19–21 min

↓

Cool the distillate at 15°C for 10 min; mix and filter through a 9 cm Whatman No. 4 filter paper as before

↓

Titrate 100 ml of the filtrate as in the R.M. value, using 0.05 N barium hydroxide; carry out a blank determination similarly

Calculation

The source’s printed expression for the Kirschner value is garbled in the available text. It is carried below as printed, with the terms defined as the source defines them:

Kirschner value = (T₁ − T₂) + [100 − (T₃ − T₄)] × 121 / 10,000

Where,

• T₁ and T₂ = sample and blank titres respectively in the Kirschner value determination
• T₃ and T₄ = sample and blank titres respectively in the R.M. value determination

Note: the printed formula is not fully legible; the procedure and the term definitions are as the source gives them. Do not apply this calculation without confirming the expression against the printed book.

References

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