SOP: Determination of Recoverable Oil in Citrus Juices by Steam Distillation

GIFSQ — Global Institute for Food Safety & Quality

Principle

Peel oil is co-distilled from the juice with steam and collected in a graduated receiver, where the volume of separated oil is read directly. This is the steam-distillation (CSIRO) method for recoverable oil in citrus juices.

Apparatus required

• 2-litre flask (steam generator)
• 5-litre flask containing the juice sample
• Spray tube extending nearly to the bottom of the 5-litre flask
• Still head and 18-inch condenser
• 1000-ml Wilson flask (oil receiver), discharging into a 125-ml graduated cylinder

Procedure

Clean the condenser thoroughly before beginning

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To the 2-litre flask add 1 litre of water; connect it by a glass or rubber tube to the spray tube entering the 5-litre flask containing exactly 3 litres of citrus juice

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Connect the outlet tube from the sample flask to the still head and the 18-inch condenser, discharging into the 1000-ml Wilson flask, which discharges into the 125-ml graduated cylinder; fill the Wilson flask with distilled water

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Bring the water in the steam generator to boiling and simultaneously heat the juice nearly to boiling by direct heat

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Close the steam generator so the steam passes through the sample and then through the condenser; withdraw the direct heat from the sample during the early part of the distillation, and apply heat again if excessive condensation occurs in the sample flask

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Adjust the boiling rate so that condensation of the distillate is complete in the upper half of the condenser and the distillation finishes in about 20 minutes

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Continue distillation until 125 ml of water has collected in the graduated cylinder

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Tip the Wilson flask to bring the oil layer within the graduation marks, let stand for 10 minutes, and estimate the volume of oil to the hundredth of a millilitre

Calculation

Recoverable oil, % (v/v) = millilitres of oil recovered × 0.0333

Precautions

• Clean the condenser before every run — carry-over of oil from a previous run inflates the result.
• Keep the distillation rate as specified; too fast a boil drives water over before the oil separates cleanly.

References

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

Standard Methods for the Analysis and Examination of Foodstuffs, C.S.I.R.O., Australia, 4th edn., p. 9 (1952) — as cited in the book.