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Protein and lipids in milk

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Aim: Complete an experiment to find the percentage of protein and fat within skimmed milk and the unknown milk. Then taking the literature values of skimmed, semi-skimmed and full fat milk compare it to the result of our unknown milk and decide which of the three milks it is Procedure A clean dry 250cm� beaker was placed on a balance. Tare the balance then approximately 100cm� was place in the beaker. The exact mass was recorded The beaker was placed on a hot plate and ethanoic acid was added and stirred until the fat and protein in the milk began precipitate. The mixture was cooled in an ice bath without disturbing the mixture. Once the mixture was cooled a beaker was set up with muslin and filtered the protein and fat the dried between filter paper. The solid was the placed in a clean dry 250cm� beaker. To remove the adhering fat from the protein, 50cm� of propanone was added to the precipitate and the solid was broken into small pieces. The beaker was placed on a hot plate in a fume cupboard and heated gently and stirred. When the solution came to a boil the beaker was removed. The beaker was then boiled again and repeated the same procedure three more times. The propanone was replenished to its original volume. The protein was filtered under pressure and washed with a small amount of propanone. ...read more.


The results of our protein could be inaccurate as in the procedure * The beaker was placed on a hot plate and ethanoic acid was added and stirred until the fat and protein in the milk began precipitate The protein may not have coagulated as we may not have heated the mixture for long enough or we may not have stirred it. The results for out fat could be inaccurate due to the need for the fat to stick to the protein, so if this didn't happen fully, immediately some fat would be filtered off. Not all the fat that was stuck to the protein separated as when we used propanone to do solvent extraction, if the surface area of the protein was small if we didn't break the protein up enough the amount of fat released was reduced as the propanone could not reach the fat that was in the centre of the large pieces of protein. Along with the errors within the procedure, we lost a large amount of protein as when we used the reduced pressure filter we pulled the Buchner funnel out of the flask and spilt the protein. Because of this our protein value could be lower then thought. Although there were many procedural errors, within my experiment i did carry out some actions to ensure accuracy. Firstly I used an ice bath to cool down the mixture before filtering it. ...read more.


results and my results I can see that both the protein and lipid values of my results are noticeably lower as my results of skimmed milk's protein is: 2.38 where as the literature value is 3.5, so my result is closer to the literature of the full fat milk, which has a value of 3.3. The literature value of lipids in skimmed milk is 0.3 where as my results are 0, which could be as the balance wouldn't read the small amount, but my value is considerably closer to the literature value of skimmed milk then that of the others. My results been lower than that of the literature values could be caused by both procedural error and percentage error of my equipment. Taking this into account I am able to compare the unknown milk to the literature values and decide that the unknown milk is semi-skimmed milk. I have decided this as even though the lipid values of the unknown milk is nearest to the literature values of skimmed, it is slightly larger, and as within the experiment we were likely to loose material, meaning that the value of the protein is too high, and the protein value is also a lower value. Even though the value of the protein for full fat is near to that of the unknown milk, the lipid value is too different. Meaning the unknown sample is likely to be semi-skimmed milk. ?? ?? ?? ?? Introduction Assignment ...read more.

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