1. Lab Activity 4 A. Extraction & Determination of Crude Fat from Plant or Animal Tissues B. Determination of Dry Matter and Moisture Content In Plant Materials C. Determination of dry matter & Moisture in Meat
IUG, Fall 2012
Dr. Tarek Zaida

2. A. Extraction & Determination of Crude Fat from Plant or Animal Tissues
A Soxhlet extractor is a piece of laboratory apparatus invented in 1879 by Franz von Soxhlet.
It was originally designed for the extraction of a lipid from a solid material.
However, a Soxhlet extractor is not limited to the extraction of lipids.
Typically, a Soxhlet extraction is only required where the desired compound has a limited solubility in a solvent, and the impurity is insoluble in that solvent.
If the desired compound has a significant solubility in a solvent then a simple filtration can be used to separate the compound from the insoluble substance.

5. A solid material containing some of the desired compound is placed inside a thimble made from thick filter paper, which is loaded into the main chamber of the Soxhlet extractor.
The Soxhlet extractor is placed onto a flask containing the extraction solvent.
The Soxhlet is then equipped with a condenser.
The solvent is heated to reflux. The solvent vapour travels up a distillation arm, and floods into the chamber housing the thimble of solid.
The condenser ensures that any solvent vapour cools, and drips back down into the chamber housing the solid material.

6. The chamber containing the solid material slowly fills with warm solvent.
Some of the desired compound will then dissolve in the warm solvent.
When the Soxhlet chamber is almost full, the chamber is automatically emptied by a siphon side arm, with the solvent running back down to the distillation flask.
This cycle may be allowed to repeat many times, over hours or days.
During each cycle, a portion of the non-volatile compound dissolves in the solvent.
After many cycles the desired compound is concentrated in the distillation flask.
The advantage of this system is that instead of many portions of warm solvent being passed through the sample, just one batch of solvent is recycled.

7. Cool to room temperature and weigh the extraction flask.
At the end of extraction (some 12 hours), the extraction flask is removed from the apparatus, then heated on a hot plate under the hood until most of the solvent has evaporated and before complete dryness.
Place the extraction flask containing the crude fat in an oven for 30 min at 70 C
Cool to room temperature and weigh the extraction flask.
Calculate the percentage of crude fat in the air-dried sample.
Crude fat % = (wt of ext. flask + crude) – (wt. of ext. flask) x 100
wt. of sample

8. B. Determination of Dry Matter and Moisture Content In Plant Materials
Air dried food (plant) material (ground samples),
oven 105 C,
Porcelain crucibles (25 ml)

9. 1. weigh 2 clean dry crucible
Procedure
1. weigh 2 clean dry crucible
2. Place about 2 g of food material in the crucible
3. Place crucible and sample in an oven, set at 105 C overnight (12 h)
4. Cool in a desiccator and weigh crucible plus dry sample
Calculations:
Dry matter% = wt. of crucible + wt. of dried sample) – (wt. of crucible) x 100
Wt. of sample before drying

10. C. Determination of dry matter & Moisture in Meat
Procedure
At 103 C dry 15 g acid washed sand in a flat metal dish together with a thin glass rod
Cool and weigh the dish and contents
Weigh in 5 g prepared sample and add 5-10 ml ethanol, mix the mass thoroughly with the glass rod
Place the dish on a water bath at C, remove the alcohol by evaporation and stir occasionally.
Heat the dried mass at 103 C for 2 hours in a drying oven.
Cool in a desiccator and weigh, repeat drying and weighing until successive weightings differ by less 0.1% of the mass of the test portion.
Calculate the moisture percent in the meat sample