Determination of Saponification Value of a Fat or Oil
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Determination of Fat
Name: T.L.V.Peiris Index No:
GS/MSc/Food/3630/08
Date Performed: 05/12/2009
Introduction Fat is important to all aspects of meat production and processing. Fresh and frozen meat prepared for manufacturing purposes is specified in terms of fat content (expressed as chemical lean). This is an important specification of commercial trading as well as being an important technical specification for product end-use. Manufacturing meat that is traded as a commodity on the international market is specified in terms of its fat content (expressed as chemical lean) and this is one of the primary product testing criteria for product. Apart from the commercial importance of the fat content of unprocessed meat, especially manufacturing meat, fat content is an important technical and regulatory specification for almost all processed meat products. The “Soxhlet” method is recognised by the Association of Official Analytical Chemists (AOAC) as the standard method for crude fat analysis. Crude fat content is determined by extracting the fat from the sample using a solvent, then determining the weight of the fat recovered. The sample is contained in a porous thimble that allows the solvent to completely cover the sample. The thimble is contained in an extraction apparatus that enables the solvent to be recycled over and over again. This extends the contact time between the solvent and the sample and allows it time to dissolve all of the fat contained in the sample. In order for the solvent to thoroughly penetrate the sample it is necessary for the sample to be as finely comminuted as possible. Before the solvent extraction step can begin the sample must be dried. Often a moisture analysis is required as well as a fat analysis and this can be achieved by accurately weighting the sample after drying and before extraction, as well as before drying. If a moisture analysis is not required the sample need only be weighed before drying and again after solvent extraction. In either case the sample must be weighed accurately on an analytical balance at each stage of the analysis. When the sample is being weighed it is important not loose any part of it including any moisture that may weep from the sample during weighting. Loss of this moisture can be avoided by weighing the sample directly into a pre-dried extraction thimble or alternatively on to a pre-dried filter paper. If a moisture analysis is required, the dried extraction thimble or filter paper also has to be pre-weighed. After weighing, the sample (in the thimble or filter paper) can be placed in the oven for drying. After drying, the sample can be placed directly into the distillation apparatus for extraction. Determination of total fat content by acid hydrolysis This method is suitable for the determination of total fat content of a wide range of foods including chocolate, confectionery, nuts, biscuits, fruit and vegetable products, meat and meat product and milk products. Principal of method The product is hydrolysed with hydrochloric acid and filtered. The dried mass containing the fat is extracted with petroleum ether, the solvent evaporated and the residue weighed. Determination of Fat
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Determination of crude fat Materials and method Materials 1. 2. 3. 4. 5. 6. 7.
Method Around 6g of finely chopped sample was added into a motor and around 12g of sodium sulphate was added . Then this was grounded until a free flowing powder is obtained. All powdered materials were transferred to the extraction thimble and the end was plug by cotton wool. The extraction thimble with with the sample was placed in soxlet apparatus. To the round bottom flask (250 ml) which was previously dried pumic chips were added and weighed 200ml of petroleum ether was then added to the round bottom flask and fixed it to soxlet apparatus. Then fefluxed for 5hours. After refluxing the solvent was distilled off and placed the flask and content in an oven at 105 oC for two hours. The flask was cooled and weighed. This was repeated until a constant weight was obtained. Calculations Weight of flask with fat and chips (X) = 98.0884g Weight of flask and chips Weight of sample
(Y) = 97.1529g (W) = 6.4680g
% Crude fat content of the sample = (X-F) X 100 W
= 98. 0884g-97.1529g X 100 6.4680g = 14.47 %
Determination of total fat Materials Beakers (100ml) Majonnier flasks Hydrochloric acid Petrolium ether Determination of Fat
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Ethanol Methods 2g of sample was placed in a 100ml beaker and 2ml of 95% etyl alchol and 10ml of 6M HCl was added. Contents were thoroughly mixed and placed the beaker on a water bath ( 70-80oC) and stir the content for about 30-40 mins frequently. The beaker was removed from the water bath and cooled to room temperature and 10 ml of EtOH to it and transferred the mixture into the majonnier flask. The beakers was washed with 25 ml of diethyl ether in three portions and added it to the flask and stopper the flask with a cork and shaken vigorously for about 1 min. then 25 ml of pet ether was added and shaken for 1min. Then the flask was kept undisturbed until the upper ether layer was clear. The upper ether was then removed into cleaned dried weighed flask. This was then dried in a water bath at 80oC until a constant weight is obtained. Calculations
% Total Fat = Wt. Of Fat X 100 Wt. of Sample
m0 = weight of empty flask m1 = weight of empty flask + Extracted fat
2.0521g = 16.72% Mean value of results = 16.72% + 17.60% + 17.22% 3 = 17.18%
Conclusion Total Fat content of sausage = 17.18% Crude fat content = 14.47% Discussion Soxhelt method only gives us the free fatty acid amount of the sample. But total fat extraction method results in both free and bound fat this reason for higher values in total fat. EtOH is used to precipitate the fat. Diethyl ether absorbs water and make sample dry. The combination of pet ether and diethyl ether facilitate extraction of fat.
