B.DETERMINATION OF CASEIN FROM MILK WITH AN ACID (VINEGAR) INTRODUCTION Milk is the most nutritionally complete food found in nature. All kinds of milk, human or animal, contain vitamins (principally thiamine – VitB1, riboflavin – VitB2, pantothenic acid – VitB5, and vitamins A, B12, D), minerals (calcium, potassium, sodium, phosphorus, and trace metals), proteins(mostly casein), carbohydrates (principally lactose), and lipids (fats). Whole milk is an oil-in-water emulsion, containing its 3.9% fat dispersed as micronized globules. The fat emulsion is stabilized by complex phospholipids and proteins that are adsorbed on the surfaces of the globules. Because the fat in milk is so finely dispersed, it is digested more easily than fat from any other source. The globules are lighter than water, thus coalesce on standing and eventually rise to the surface of the milk as cream. Vitamins A and D are fatsoluble substances and are thus concentrated in the cream. The fats in milk are primarily triglycerides, which are esters of saturated and unsaturated carboxylic acids with glycerol, a trialcohol. OBJECTIVE To determine a casein from milk with an acid (vinegar). MATERIALS / APPARATUS Soymilk Pasteurized whole milk Vinegar pH meter pH buffer 4 and 7 11ml of vinegar is added to the warm milk and stirred for 2 minutes. e ed e . The cheesecloth over the top of the beaker is fasten using the rubber band 10. The pH meter with pH buffer 4 and 7 is calibrated 2. The pH of the milk is measured 5. The weight of 120 ml of milk in the beaker is weighed and recorded. The plate is turned off and the beaker is removed 6. The casein is squeezed until almost dried and the cheesecloth is spreader out to let the casein dry for 5 minutes 13. and then the milk is allowed to sit for 5 minutes. The empty beaker is weighed and the weight is recorded 3. the curds are collected in the cheesecloth and the vinegar and whey is allowed to drain off into the bottom of the beaker. 4. The beaker with the milk is placed on a hot plate. The remaining liquid was the whey. 7. The precipitate is weighed. 12. Beaker . A piece (2-3 layers) of cheesecloth is cut out to cover the top and 2 inches down the sides of a beaker. The pH of the liquid portion is measured again 8. The casein is precipitated into heavy white curds. 11. 9. The curdled milk is poured into the beaker. The cheesecloth is gathered up with the casein and rinsed in cool water by dipping into another beaker containing water. 250 ml PROCEDURE 1. 4. 6.0757 Colour of curd or casein Texture of curd or casein Creamy Yellow Colour Harder . pH after added acid and after heated 1. 4. 124.7 C 1.44 . 125. 36.18 2. C 1.9290 2.56.92 .6298 2.RESULTS Determination of Casein in Whole Milk and Soymilk Whole Milk pH before added acid and before heated 3.99. 32.21 Weight of curd or casein 1.3 C Weight of milk 1. 18. 6. 3. 121.88 . 1.21 3. 121.94 . 24.70.8 C 2. 37. 16. 17.97 3.0 C 3.8957 Creamy White Colour Soft 2.82.7700 3. 120. 4. 4.36 1. 16.90 Soymilk 1. 6. 26.5392 3.29 2. 33 C 3. 30. 123.3 C 3. 4. 4. But there is a difference in weight of casein for whole fat milk and soy milk . This result is error because time of drying does not enough and the temperature use is too low. The whey proteins were separated into globulin and albumin fractions. We use whole milk and soy milk as our sample for this experiment.5392 compare to whole fat milk which is 17. Casein is dispersed in milk in the form of micelles.9290 and 3. The colour also are different where by whole fat milk give a creamy yellow colour and soymilk give a creamy white colour .85and after added acid (+) heated is 4.DISCUSSION For this experiment.98 and 4. Casein was first separated from milk by adding acid to milk. As the general. Milk composed of many protein . there have error for trial one and three.Casein and whey protein is the main groups. The micelles are stabilized by c en en re e Κ- ydr p b c bu Κ-casein contains a hydrophilic portion known as the glycomacropeptide and it is this that stabilizes the micelles when the pH of milk is changed. the acidic or basic groups of the proteins will be neutralized.91.The texture of casein for soymilk is soft compare to whole fat milk which is harder . Proteins are polymers of amino acids. The value we get is 1. Casein is easily separated from milk.Soy milk has lower quantity of casein which is 16. The whey proteins are also made up of a number of distinct proteins. For the determination of casein from milk with an acid. While for casein. either by acid precipitation or by adding rennin.8957. It was subsequently shown that casein is made up of a number of fractions and is therefore heterogeneous. For soy milk. thus establishing its existence as a distinct protein. we have learned how to determine casein from milk with an acid (vinegar).57. While for soy milk is 6.4918. the pH of whole fat milk before added acid is 6. . it will contaminate the milk and eventually change the odor and flavor of the milk making it tastes sour. either by acid precipitation or by adding rennin.At the pH at which the positive charge on a protein equals exactly the negative charge. What causes the reduction in the pH of milk? The reduction in the pH of milk is primarily caused by bacteria present in milk or its surrounding. We are also able to observe the texture of the casein after added acid and heated. When increasing the period of the day. As the pH falls the charge on casein falls and it precipitates. The objective was accepted. That is when the pH of milk will start to decrease. QUESTION 1. As the bacteria grow and multiply in the milk. If an acid is added to milk. CONCLUSION The objective of this experiment is to determine the pH of milk and to determine casein from milk with an acid (vinegar). the milk goes sour. This pH is called the isoelectric point of the protein (pH 4. the pH falls. or the casein precipitates more completely at low pH. or if acid-producing bacteria are allowed to grow in milk. it is easily separated from milk. For Casein. The pH of milk changes over time.6 for casein). Hence milk curdles as it sours. . the net total charge of the protein is zero. it becomes more acidic and the pH gets lower. org/AE/AEPC/IFT/unit_three. Temperature.ca/foodscience/cheese-making-technology/section-c-milk/rawmilk-quality/milk-growth-medium 5) http://www.uu.library.unm. W e p r nce’ fc en n e f d industry? Casein is used in the chemical industry and as a glazing additive in paper manufacturing.uoguelph. acidity.accessexcellence.picotech. List 3 factors that influence the precipitation of casein in milk. REFERENCE 1) http://biology. 4.html 2) http://www.html .php 3) http://dspace.edu/ccouncil/Biology_124/Summaries/Macromol.2. and calcium content of the milk.com/experiments/ph_of_milk/results.nl/handle/1874/765 4) https://www. Compare the amount of acid casein precipitate from the low fat with the amount of soy protein coagulated from the soymilk? How do your result compare with the nutrition facts label for each product? 3.
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