SOP: Determination of Moisture in Pectin

GIFSQ — Global Institute for Food Safety & Quality

Principle

The pectin sample is dried in vacuo at 100°C; the loss in weight gives the moisture content. Because drying at 100°C degrades the pectin, samples intended for further measurements are dried under milder conditions instead.

Apparatus required

• Tared metal dish (5 cm in diameter, with cover)
• Vacuum oven (5 to 20 mm Hg)
• Desiccator
• Phosphorus pentoxide (for the desiccator)

Reagents

a. Phosphorus pentoxide (for the desiccator).

Sample preparation

Grind the sample to pass 80-mesh.

Procedure

Weigh 1 g of the 80-mesh sample into the tared metal dish (5 cm in diameter, with cover)

↓

Dry in vacuo (5 to 20 mm Hg) for 4 hr at 100°C

↓

Cool in a desiccator over phosphorus pentoxide and weigh

Precautions

• Do not use the sample dried at 100°C for subsequent measurements, as the pectin would have been degraded.
• If the sample is to be used for other measurements, dry it at 70°C for 16 hr instead.
• Add 1% to the per cent moisture observed to obtain agreement with the Fischer method.
• Determine the moisture content and apply a correction for it in all other analyses and physical measurements.

References

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

Johnson, C.M., Ind. Eng. Chem., Anal. Edn., 17, 312 (1945) — cited in the book.