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Determination of volatile oil in spices

INTRODUCTION

Volatile oil content is a measure of aroma strength of spices and condiments. The volatile oil content in different spices ranges from 1 to 12%. The volatile oil content varies with source, variety and seasons.

PRINCIPLE

The method involves distilling the volatile oil over with boiling water, condensing and collecting the oil in a measured volume of xylene in a graduated tube, after cooling, direct reading from the volume of volatile oil separated from the distillate.

REQUIREMENTS

Apparatus
Volatile Oil Traps-Clevenger-type with joints.
Flask with Magnetic Stirrer-1 litre capacity round bottom and short-neck wit standard joint and having egg-shaped magnetic stirrer bar.

Reagents

Xylene (AR grade)

PROCEDURE

Transfer enough weighed sample to 1 litre flask to yield 2 to 4 ml volatile oil.

Add water to fill flask to half-full. Insert stirring bar and place flask in heating mantle set over magnetic stirrer. Add antifoaming agent.

Clean trap and condenser with chromic acid cleaning solution just before use and fill trap with water.

Set the apparatus so that the condensate will not drop directly on surface of liquid in trap but will run down the sides.

Start stirrer and heat mantle through variable transformer set at 90 Volts (63 Amp).

If oil separates in graduated portion of trap or clings to walls, add several drops standard aqueous detergent solution through top of condenser.

Repeat, if necessary (usually once is enough).

Distil for 10 minutes after adding detergent to wash it out of trap.

When density of oil is nearly 1 g/cc, as in cassia, or if oil separates into two fractions in trap, as in nutmeg and allspice, add 1 ml xylene, accurately measured, to lighter than water trap.

Distil, until two consecutive readings taken at 1 hour intervals show no change in oil content (taken after 6 h); cool and read the volume of collected oil.

If xylene was added, subtract its volume and report oil as ml per 100 g spice.

Note 1: With the material containing volatile oils lighter than water and fixed oils heavier than water like nutmeg, discontinue distillation when the fraction of oil obtained during 1 hour is heavier than water.

Note 2: To correct the unsatisfactory separation of oil and water, agitate the liquid in the trap with a copper wire through the condenser top. Measure the oil in the trap after allowing to stand until it is cooled. Report volatile oil in ml per 100 g of the material

CALCULATION

where,
a = volume, in ml, of steam volatile oil collected through steam distillation; and
b = mass, in g, of the sample taken.

RESULTS AND INFERENCE

Measure the volume of the oil estimated to the nearest 0.02 ml. The difference between two single and independent results found by two analysts working in different laboratories on identical test material should not exceed 0.5 ml. Spices having strong aroma have higher content of volatile oil.

PRECAUTIONS

• The apparatus should be cleaned before each distillation.
• Clear separation of water and volatile oil is essential.
• Distillation should be continued until successive readings of the volume of volatile oil are the same.

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