Lipids are groups of substance which can be dissolved in organic solvents such as ether, chloroform, and other organic substances. It is a broad group of naturally occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The main biological functions of lipids include energy storage, as structural components of cell membranes, and as important signaling molecules.
Soxhlet extraction is a 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.
To determine the content of lipid has been one of the important standardizations in food industry. An accurate and quantitative method to determine the content of fat and oil is the Soxhlet extraction. The Soxhlet extraction allows the calculation of total lipid (fat) content in food substances. The present experiment involves the extraction of fat from commercial French fries and potato chips by the Soxhlet extractor apparatus.
Food sample from package was mashed and grinded using the mortar and pestle. About 10.0g of the crushed sample was weighed in analytical balance. 1:1 (w/w) of sodium sulfate was added and mixed with crushed samples in cellulose thimble.
After thoroughly mixed of sample with sodium sulfate, sample was tapped down gently and a plug of glass wool was placed on top of the thimble to prevent spillage.
A flat-bottomed flask with anti-bumping granules was weighed. [Pre-weigh->data 1]
A Soxhlet extractor was set up. 2 rounds of petroleum ether solvent were poured into the thimble. Water flow was turned on after the connection
The flat-bottomed flask was heated. The solvent was brought to vaporization without boiled. The sample was flushed by the solvent every 5-10 minutes. The whole apparatus was monitored continuously to ensure no vapor flow out of the condenser.
The extraction was continued for 1-2 hours.
The flask was picked out from the set up. The thimble was picked out from the apparatus. The remaining solvent was poured out from the apparatus to the flask.
The solvent was removed by steam-bath heating in flame hood for about 30minutes. Then the flask was putted in 100°C oven for 5 minutes for complete removal of water in the flask.
The flask was cooled down and weighed. [Data 2]
The fat contented was calculated in food sample.
All the lipid sample was kept in a clean capped test-tube(4°C, wrapped) for the next experiment.
Results
Group
Food sample
Weight of Food used(g)
Weight of flask+ anti-bumping granule (g)
Weight of flask+ anti-bumping granule+ food sample (g)
Remark
(any sample loss?)
1
Chips
10.0038
96.7715
99.1759
N/A
2
Chips
10.0060
98.2992
100.9885
N/A
3
Fries
10.0600
91.4608
95.6817
N/A
4
Fries
10.1159
94.8433
99.3668
N/A
5
Fries
10.0845
96.3123
99.3827
Sample loss
Calculations
Chips sample:
Group1,
(99.1759-96.7715)/ 10.0038 *100= 24.0349% Fat(w/w)
Group2,
(100.9885-98.2992)/10.0060*100= 26.8769% Fat(w/w)
Average fat content in chips sample:
(24.0349+26.8769)/2= 25.4559% Fat(w/w)
Fries sample:
Group3,
(95.6817-91.4608)/10.0600*100= 41.9573% Fat(w/w)
Group4,
(99.3668-94.8433)/10.1159*100= 44.7167% Fat(w/w)
Group5,
(99.3827-96.3123)/10.0845*100= 30.4467% Fat(w/w)
Because group 5 has sample loss due to careless mistakes, so we omit the calculation of group5.
Average fat content in fries sample:
(41.9573+44.7167)/2= 43.3370% Fat(w/w)
Discussion and Questions
Why sodium sulfate is added?
Drying the food at elevated temperatures is undesirable because some lipids become bound to proteins and carbohydrates, and bound lipids are not easily extracted with organic solvents. Sodium sulfate will be unaffected by the organic solvent but will scavenge excess water from the sample. Most of foods contain a certain percentage of water. Removal is necessary either prior to or, in this case, during the extraction to prevent mixture of immiscible solvents or lengthy drying time of final product.
Compare and discussion the %Fat (w/w) of the 2 food samples
25.4559% Fat(w/w) was found in the chips sample. 43.3370% Fat(w/w) was found in the fries sample.
In contrast, fat content in fries sample is higher than that of chips sample.
43.3370-25.4559= 17.8811%Fat(w/w)
Fries sample contain more fat than chips sample 17.8811%Fat(w/w). Also, from the reference value, 43.3370%Fat(w/w) is higher than daily energy intake(30% Fat(w/w))from fat sources. Eating fries sample is unhealthier than chips sample.
What are the possible errors in this fat extraction technique? Any possible precautions should be noticed in order to get a proper comparison between the food samples?
Some evaporation of solvent has been observed if the temperature of the heater is too high. It was necessary to control the temperature of heater properly. There are many joints in the soxhlet extractor. Care should be taken to ensure a good sealed joint. In order to increase the precision, doing more samples is necessary. Wash all the soxhlet glassware with petroleum ether before experiment to prevent contamination. It is better to hold the thimble with forceps because if our hand contains oil or fat, result in contamination.
Conclusion
25.4559% Fat(w/w) was found in the chips sample. 43.3370% Fat(w/w) was found in the fries sample.
