BCH 212: The isolation of casein from milk PDF

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it is about the isolation of casein from milk and to calculate the percentage yield of the milk...

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NAME:

MTONGA A

STUDENT NUMBER: 202016684

COURSE:

BCH 212

DATE:

05 JUNE 2021

EXPERIMENT:

6

TITTLE: The isolation of casein from milk. INTRODUCTION Milk is a nutrient-rich white liquid which is produced by female mammals in the mammary glands and secreted by the breasts. Milk is the most nutritionally complete food found in the world. It contains lactose, fats, vitamins and proteins. The milk’s constituents help the in nourishment of the suckling young, they are a source of protein. Dairy products (milkcontaining) help in prevention of osteoporosis, bone fractures and strong teeth. Milk contains 3,3% total protein. There are two types of proteins in milk which are casein and whey proteins. These proteins are all globular which means they fold onto themselves into compact spherical units. They contain all the essential amino acids. Amino acids are the building blocks of proteins that are linked by peptide chains. Whey protein which makes up 20% of bovine milk is made up of αlactalbumin (ALB) and β-lactoglobulin (BLG) in different proportions (Dalgeish, 1997). Whey protein digests more quickly in the body. ALB is an albumin which is a protein produced by the liver and secreted to the bloodstream. It improves the immune responsiveness, increases glutamione which helps fight against viruses in animals as well as prevent tumours which may be cancerous in humans. The BLG is a major component of the top layer of milk, coagulation and denaturing when the milk boils. It forms a thin gelatinous layer on the surface of milk. The other protein which is casein that is made up of α-casein, β-casein and k-casein. This protein makes up to 80% bovine milk. It is largely responsible for the white colour of milk. When exposed to heat or acid it coagulates and appears as elastic material which can be removed (Whittemore, 2019). Coagulation is the process whereby a gel is formed by destabilizing casein micelles causing them to aggregate and immobilize water and trap fat molecules in the new formed matrix. Casein proteins coagulate at a pH that is approximately 4,6(Creamer, 1971). This can be achieved by enzymes, acid treatment and heat-acid treatment. Casein is used as a supplement because it is a slow-digesting dairy protein. It releases amino acids slowly and reduces muscle breakdown while you sleep, hence it should be taken before bed (Mawer, 2016). It contains all essential amino acids with the exception of cysteine. Casein was used in textile industries to provide paper, textiles, paints also leather

(Sarode, 2016). Casein is isolated from milk commercially and is important in industry because after dissolving in alkaline solutions and drying, it becomes a sticky substance that can be used in glues, the coating of paper, and binding of colours in paints and wallpaper. AIM The aim of the experiment was to isolate casein from milk and calculate the percentage yield of the protein in the milk.

METHOD AND MATERIALS Hundred ml of milk was placed in a 500ml clean beaker and warmed to 50 0C in the hot plate. About 40ml of 10% acetic acid (10ml acid + 90ml of water) was also warmed and added in the milk slowly whilst stirring the solution. The final pH of the mixture was measured using pH meter and it was 4,8. They left the suspension to cool to room temperature at 25 degrees Celsius and then stand for another five minutes to cool. The suspension was filtered using a muslin cloth. The precipitate was washed 3 times with a 30 ml volume of water and it was then suspended it in about 30ml of ethanol. The suspension was transferred in a filter paper and it was filtered on a Buchner funnel. Equal volumes of ethanol and ether (30 ml +30 ml) was poured in the suspension there after 60 ml of water was poured. The precipitate on the filter paper was washed with 50ml of ether and it was sucked dry. The powder was removed and it was spreaded out on a watch glass to allow evaporation of the ether. The casein was weighed using a weighing balance and the percentage yield of the protein was calculated.

RESULTS

Percentage yield ( %) =

Experimental Yield (g) ×100 Theoretical Yield (g)

=

Percentage yield ( %) =

= 95,43%

3. 34 × 100 3.5

DISCUSSION Casein is an essential protein that constitutes a major part in the milk’s protein. Casein is obtained from making curdles on the milk. The milk was warmed so as to denature all the other antigens like the whey protein which are sensitive to heat and this does not affect the casein because casein is heat stable (Guanhao, 2013). The addition of acetic acid causes the pH of the solution to decrease, this converts the lactose to lactic acid and hence causing the milk to curdle. After the addition of the acetic acid the pH of the solution was 4,8. This is done so as to reach the isoelectric point of the milk whereby the net electric charge is neutral (Davies and Law, 1987). At a pH of about 4.6, the milk will coagulate to form micelles. It was washed with water three times to remove any excess acid which may be in the milk. The addition of ethanol and ether stabilises the casein micelles. The addition of ethanol removes unwanted fat from the milk, this also does not affect the casein as it is not soluble in water. The precipitate was washed with 60ml of water in the reduction in concentration of a substance dissolved in the liquid that is present in the pores of precipitate. They washed the precipitate on filter paper with 60ml of ether and dried it out because they wanted to obtain the final solid precipitate (Hupertz et al, 2014). The final % yield of the casein protein was 95,43%. The casein makes up about 80% of the proteins found in milk (Gellrich et al, 2014). The percentage yield obtained was relatively higher. This must have been due to some antigens not being all removed at some stage or the milk had a high content of the casein protein. A similar experiment was conducted by Daniel, (2018) and the results were almost the same. He managed to get 89.93% percentage yield whilst the calculated percentage yield in this experiment was 95.43%. The difference may be due to difference in the source of the milk, human error whilst conducting the experiment or different pH of the milk after addition of the acetic acid, this affects the solubility of casein in turn the amount of precipitate (Davies and Law ,1987). The results he got were closer to the results obtained in this experiment which would hence mean that the experiment was a success because a similar percentage of casein was obtained.

REFERENCES Creamer L.K (1971). A further study action of renin on beta-casein. Dairy Science Technology 11(30). Dagleish D.G, Senaratne V and Francois S (1997). Interactions between α-lactalbumin and βlactoglubulin in the early stages of heat denaturation. Journal of Agriculture and Food Chemistry. 45(9), 3459-3464. DOI: 10.1021/jf970113a. Daniel B (2018). Casein: The isolation, Hydrolization and Neutralisation of it from Non-fat Milk (Magic Milk). Expt 1 report biochemlab-Academia.edu. Davies D.T and Law A.J (1987). Quantitative fraction of casein mixtures .J Dairy Res 54(396) Gelrich K, Meyer H.D, and Wiedmen H (2014). Characteristics of edible foods of animal origin:Milk. Food Chemistry 2nd ed. Marcel Dekker Inc. New York. Guanhon A, (2013). Phosphoprotein in milk Food Science Research 20(22). Huppertz T, Grosman S, Fox PF, Kelly AL (2004). Heat and ethanol stabilities of high-pressuretreated bovine milk. Int Dairy J. 14:125–133. Mawer R (2016). Why Is Casein One of The Best Proteins You Can Take? Available from: https://www.healthline.com/nutrition/casein-protein-is-highly-underrated [Accessed 04 June 2021]. Sarode AR, Sawale PD, Khekdar CD, Pawshe RD and Kalyankar SD (2006). Casein & Caseinates: Methods of Manufacture. Encyclopedia of Food and Health. Pp: 676-682. DOI: https://doi.org/10.1016/B978-0-12-384947-2.00122-7. Whittemore

B

(2019).

Chem35

Synthetic

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http://courses.chem.psu.edu/chem35/HTML/Experiments/Exp112.pdf.

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