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Chemistry Project Analysis of the different samples of milk for presence of Casein Friday, 6 December 2013
Blog Archive ▼ 2013 (2)
ABSTRACT OF REPORT
▼ December (2) ... ...
About Me Patit Pawan Barik
Milk is the best and cheapest source of nutrition and an article of daily diet, easily accepted and used by all the age groups in rural as well as in urban areas. It provide appreciable amount of fats and protein and also provides body building vitamins along with furnishing energy giving lactose and many other nutrients, therefore an ideal food for pregnant female and infants. Milk can provide a wide range of readily available nutrients to maintain health and normal growth of body. Milk has no pronounced taste what is slightly sweet to most persons. Milk is the largest and the single most important commodity within the livestock sector. Although slightly varies in composition and properties, the milk of different species contain the same constituents in general. On average, milk is made up of 87.4% water and 12.6% milk solids (3.7% fat, 8.9% milk solids-not-fat). The milk solids-not-fat contain protein (3.4%), lactose (4.8%), and minerals (0.7%). Milk fat often called “butter fat” is commercially, the most valuable constituent of milk. It is also of great importance from the standpoint of the food value of the milk. The agreeable flavour of rich milk and to a large extent of other dairy products is largely due to the milk fat. Proteins are among the most complex of organic substances. They contain carbon, hydrogen, oxygen, nitrogen, sulphur and sometimes phosphorus. The protein of milk is not a single compound but includes two major proteins and small quantities of others. Between them casein constitute about 80 % of the total and lacto albumin 18%. A third protein recognized as present in
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milk is lacto globulin. It is present in very small amounts, probably about 0.05 to 0.07 %. Ash constituents of milk are extremely important in their relation to the heat stability of the milk.
ANALYSIS OF DIFFERENT SAMPLES OF MILK FOR PRESENCE OF CASEIN A File Report submitted to :
______________ ______________ Internal Examiner
______________ _______________ Head Of Chemistry Department Principal
CERTIFICATE This is to certify that this dissertation titled “Analysis of different samples of milk for presence of Casein” was submitted by Patit Pawan Barik to
Head of Chemistry Department of Kendriya Vidyalaya, Chittaranjan, W.B. carried under guidance and supervision during the Academic year 2013-2014.
ACKNOWLEDGE MENT I wish to express my deep gratitude and sincere thanks to the Principal, Kendriya Vidyalaya, Chittaranjan, W.B. for his encouragement and for all the facilities that he provided for this project work. I sincerely appreciate this magnanimity by taking me into his fold for which I shall remain indebted to him. I extend my hearty thanks to Mr. K.Batabyal (PGT Chemistry), who guided me to the successful completion of this project. I take this opportunity to express my deep sense of gratitude for his invaluable guidance, constant encouragement, constructive comments, sympathetic attitude and immense motivation, which has sustained my efforts at all stages of this project work.
DECLARATION I do hereby declare that this project work has been originally carried under the guidance and supervision of Mr. K. Batabyal (PGT Chemistry), Head of Chemistry Department, Kendriya Vidyalaya, Chittaranjan, W.B.
Patit Pawan Barik XII ‘A‛ Roll no.- 32
TABLE OF CONTENTS Introduction
Aim
Requirement
Theory
Procedure
Observations
Conclusion
Reference
INTRODUCTION Milk is a food of exceptional interest. Not only is milk an excellent food for the very young, but humans have also adapted milk, specifically cow‛s milk, as a food substance for
adapted milk, specifically cow‛s milk, as a food substance for persons of all ages. Many specialised milk products like cheese, curd, butter and ice cream are staples of our diet. Milk is probably the most nutritionally-complete food that can be found in nature. This property is important for milk, since it is the only food young mammals consume in the nutritionally significant weeks following birth. Whole milk contains Vitamins (principally Thiamine, Riboflavin, Pantothenic acid, and Vitamins A, D, and K), Minerals (Calcium, Potassium, Sodium, Phosphorus, and trace metals), proteins (which include all the essential amino acids), carbohydrates (chiefly Lactose), and Lipids (fats). The only important elements in which milk is seriously deficient are iron and Vitamin C. Infants are usually born with a storage supply of iron large enough to meet their needs for several weeks. Vitamin-C is easily secured through an orange juice supplement. Milk is the largest and the single most important commodity within the livestock sector. Although slightly varies in composition and properties, the milk of different species contain the same constituents in general. On average, milk is made up of 87.4% water and 12.6% milk solids (3.7% fat, 8.9% milk solids-not-fat). The milk solids-not-fat contain protein (3.4%), lactose (4.8%), and minerals (0.7%). Milk fat often called “butter fat” is commercially, the most valuable constituent of milk. It is also of great importance from the standpoint of the food value of the milk. The agreeable flavour of rich milk and to a large extent of other dairy products is largely due to the milk fat. Proteins are among the most complex of organic substances. They contain carbon, hydrogen, oxygen, nitrogen, sulphur and sometimes phosphorus. The protein of milk is not a single compound but includes two major proteins and small quantities of others. Between them casein constitute about 80 % of the total and lacto albumin 18%. A third protein recognized as present in milk is lacto globulin. It is present in very small amounts, probably about 0.05 to 0.07 %. Ash constituents of milk are extremely important in their relation to the heat stability of the milk.
Previous Experimental Observations &
Results OBSERVATIONS Average Percentage Composition of Milk from Various Mammals:
Source of milk
Water(%)
Minerals(%)
Proteins(%)
Fats(%)
Carbohydrates (%)
Cow
87.1
0.7
3.4
3.9
4.9
Human
87.4
0.2
1.4
4.0
4.9
Goat
87.0
0.7
3.3
4.2
4.8
Sheep
82.6
0.9
5.5
6.5
4.5
RESULTS The Buffalo‛s milk has highest casein presence in all the samples of milk. Therefore, buffalo‛s milk is most suitable for nutrition.
CASEIN Casein is a phosphoprotein, which has phosphate groups are attached to some of the amino acid side chains. Casein exists in milk as the calcium salt, calcium caseinate. This salt has a complex structure. It is composed of α, β, and κ caseins which form a micelle, or a solubilized unit. Neither the α nor the β casein is soluble in milk, singly or in combination. If κ casein is added to either one, or to a combination of the two, however, the result is a casein complex that is soluble owing to the formation of the micelle. The κ casein is thought to stabilize the micelle. Since both α and β casein are phosphoproteins, they are precipitated by calcium ions. The κ casein protein, however, has fewer phosphate groups and a high content of carbohydrate bound to it. It is also thought to have all its serine and threonine residues (which have hydroxyl groups), as well as its bound carbohydrates,
on only one side of its outer surfaces. This portion of its outer surface is easily solubilized in water since these polar groups are present. The other portion of its surface binds well to the water-insoluble α and β caseins and solubilizes them by forming a protective colloid or micelle around them. Since the entire outer surface of the micelle can be solubilized in water, the unit is solubilized as a whole, thus bringing the α and β caseins, as well as κ casein, into solution. Calcium caseinate has its isoelectric (neutrality) point at pH 4.6. Therefore, it is insoluble in solutions of pH less than 4.6. The pH of milk is about 6.6; therefore casein has a negative charge at this pH and is solubilized as a salt. If acid is added to milk, the negative charges on the outer surface of the micelle are neutralized (the phosphate groups are protonated) and the neutral protein precipitates: Ca2+Caseinate + 2 HCl ─› Casein + CaCl2 The calcium ions remain in solution. When milk sours, lactic acid is produced by bacterial action and the consequent lowering of the pH causes the same clotting reaction. The isolation of casein from milk will be carried out in this experiment. The casein in milk can also be clotted by the action of an enzyme called rennin. Rennin is found in the fourth stomach of young calves. However, both the nature of the clot and the mechanism of clotting differ when rennin is used. The clot formed using rennin, calcium paracaseinate, contains calcium. Ca2+Caseinate + Rennin ─› Ca2+Paracaseinate + A Small Peptide Rennin is a hydrolytic enzyme (peptidase) and acts specifically to cleave peptide bonds between phenylalanine and methionine residues. It attacks the κ casein, breaking the peptide chain so as to release a small segment of it. This destroys the water-solubilizing surface of the κ casein, which protects the inner α and β caseins and causes the entire micelle to precipitate as calcium paracaseinate. Milk can be decalcified by treatment with oxalate ion, which forms an insoluble calcium salt. If the calcium ions are removed from milk, a clot will not be formed when the milk is treated with rennin.
The clot, or curd, formed by the action of rennin is sold commercially as cottage cheese. The liquid remaining is called the whey. The curd can also be used in producing various types of cheese. It is washed, pressed to remove any excess whey, and chopped. After this treatment, it is melted, hardened and ground. The ground curd is then salted, pressed into molds, and set aside to age .It is a major protein constituent in milk & is a mixed phosphorprotein. Casein has isoelectric pH of about 4.7 and can be easily separated around this isoelectric pH. It readily dissolves in dilute acids and alkalies. Casein is present in milk as Calcium Caseinate in the form of “micelles”. These micelles have negative charge and on adding acid to milk the negative charges are neutralized. Natural milk is an opaque white fluid secreted by the mammary glands of female mammal. The main constituents of natural milk are Protein, Carbohydrate, Minerals, Vitamins, Fats and Water and are a complete balanced diet. Fresh milk is sweetish in taste. However, when it is kept for long time at a temperature of 5º it become sour because of bacteria present in air. These bacteria convert lactose of milk into lactic acid which is sour in taste. In acidic condition casein of milk starts separating out as a precipitate. When the acidity in milk is sufficient and temperature is around 36º, it forms semi-solid mass, called curd.
AIM To study the quantity of Casein in different samples of milk.
REQUIREMENTS Beakers (250 ml) Filter-paper Glass rod Weight box Filtration flask
Filtration flask Buchner funnel Test tubes Porcelain dish Different samples of milk 1 % Acetic acid solution
Ammonium sulphate solution
CHEMICAL REACTION Ca2+Caseinate2- + 2 CH3COOH(aq) ─› Casein + (CH3COO)2Ca
THEORY Casein is a phosphoprotein, which has phosphate groups are attached to some of the amino acid side chains. These are attached mainly to the hydroxyl groups of the serine and threonine moieties. Actually, casein is a mixture of at least three similar proteins, which differ primarily in molecular weight and amount of phosphorus they contain (number of phosphate groups). Casein exists in milk as the calcium salt, calcium caseinate. This salt has a complex structure. It is composed of α, β, and κ caseins which form a micelle, or a solubilized unit. Neither the α nor the β casein is soluble in milk, singly or in combination. If κ casein is added to either one, or to a combination of the two, however, the result is a casein complex that is soluble owing to the formation of the micelle. The κ casein is thought to stabilize the micelle. Since both α and β casein are phosphoproteins, they are precipitated by Calcium ions. The κ casein protein, however, has fewer phosphate groups and a high content of carbohydrate bound to it. It is also thought to have all its serine and threonine residues (which have hydroxyl groups), as well as its bound carbohydrates,
on only one side of its outer surfaces. This portion of its outer surface is easily solubilized in water since these polar groups are present. The other portion of its surface binds well to the water-insoluble α and β caseins and solubilizes them by forming a protective colloid or micelle around them. Since the entire outer surface of the micelle can be solubilized in water, the unit is solubilized as a whole, thus bringing the α and β caseins, as well as κ casein, into solution. Calcium caseinate has its isoelectric (neutrality) point at pH 4.6. Therefore, it is insoluble in solutions of pH less than 4.6. The pH of milk is about 6.6; therefore casein has a negative charge at this pH and is solubilized as a salt. If acid is added to milk, the negative charges on the outer surface of the micelle are neutralized (the phosphate groups are protonated) and the neutral protein precipitates: Ca2+Caseinate + 2 HCl ─› Casein + CaCl2 The calcium ions remain in solution. When milk sours, lactic acid is produced by bacterial action and the consequent lowering of the pH causes the same clotting reaction. The isolation of casein from milk will be carried out in this experiment. The casein in milk can also be clotted by the action of an enzyme called rennin. Rennin is found in the fourth stomach of young calves. However, both the nature of the clot and the mechanism of clotting differ when rennin is used. The clot formed using rennin, calcium paracaseinate, contains calcium. Ca2+Caseinate + Rennin ─› Ca2+Paracaseinate + A Small Peptide Rennin is a hydrolytic enzyme (peptidase) and acts specifically to cleave peptide bonds between phenylalanine and methionine residues. It attacks the κ casein, breaking the peptide chain so as to release a small segment of it. This destroys the water-solubilizing surface of the κ casein, which protects the inner α and β caseins and causes the entire micelle to precipitate as calcium paracaseinate. Milk can be decalcified by treatment with oxalate ion, which forms an insoluble calcium salt. If the calcium ions are removed from milk, a clot will not be formed when the milk is treated with rennin.
The clot, or curd, formed by the action of rennin is sold commercially as cottage cheese. The liquid remaining is called the whey. The curd can also be used in producing various types of cheese. It is washed, pressed to remove any excess whey, and chopped. After this treatment, it is melted, hardened and ground. The ground curd is then salted, pressed into molds, and set aside to age .It is a major protein constituent in milk & is a mixed phosphorprotein. Casein has isoelectric pH of about 4.7 and can be easily separated around this isoelectric pH. It readily dissolves in dilute acids and alkalies. Casein is present in milk as Calcium Caseinate in the form of “micelles”. These micelles have negative charge and on adding acid to milk the negative charges are neutralized.
PROCEDURE 1. A clean dry beaker has been taken, followed by putting 20 ml of cow‛s milk into it and adding 20 ml of saturated ammonium sulphate solution slowly and with stirring. Fat along with Casein was precipitate out. 2. The solution was filtered and transferred the precipitates in another beaker. Added about 30 ml of water to the precipitate. Only Casein dissolves in water forming milky solution leaving fat undissolved. 3. The milky solution was heated to about 40oC and add 1% acetic acid solution drop-wise, when casein got precipitated. 4. Filtered the precipitate, washed with water and the precipitate was allowed to dry. 5. Weighed the dry solid mass in a previously weighed watch glass. 6. The experiment was repeated with other samples of milk.
OBSERVATIONS According to above experiment : Sl. No.
Source of Milk
Weight of Dried Solid Mass
CONCLUSION The __________ milk has highest value of the dried solid mass i.e. the composition of Casein is highest in the sample of ________ milk.
SOLUTION TO THE ANALYSIS The ________ milk has the highest presence of casein in milk. Therefore, ________ milk is the best for nutrition.
REFERENCES Wikipedia Encyclopedia – Encarta Britannica icbse.nic.in Practical Chemistry books
This is the project created by me in Class 12th for the external practical exam. Read more » Posted by Patit Pawan Barik at 18:46
No comments:
Recommend this on Google
ABSTRACT OF REPORT
Milk is the best and cheapest source of nutrition and an article of daily diet, easily accepted and used by all the age groups in rural as well as in urban areas. It provide appreciable amount of fats and protein and also provides body building vitamins along with furnishing energy giving lactose and many other nutrients, therefore an ideal food for pregnant female and infants. Milk can provide a wide range of readily available nutrients to maintain health and normal growth of body. Milk has no pronounced taste what is slightly sweet to most persons. Milk is the largest and the single most important commodity within the livestock sector. Although slightly varies in composition and properties, the milk of different species contain the same constituents in general. On average, milk is made up of 87.4% water and 12.6% milk solids (3.7% fat, 8.9% milk solids-not-fat). The milk solids-not-fat contain protein (3.4%), lactose (4.8%), and minerals (0.7%). Milk fat often called “butter fat” is commercially, the most valuable constituent of milk. It is also of great importance from the standpoint of the food value of the milk. The agreeable flavour of rich milk and to a large extent of other dairy products is largely due to the milk fat. Proteins are among the most complex of organic substances. They contain carbon, hydrogen, oxygen, nitrogen, sulphur and sometimes phosphorus. The protein of milk is not a single compound but
includes two major proteins and small quantities of others. Between them casein constitute about 80 % of the total and lacto albumin 18%. A third protein recognized as present in milk is lacto globulin. It is present in very small amounts, probably about 0.05 to 0.07 %. Ash constituents of milk are extremely important in their relation to the heat stability of the milk.
ANALYSIS OF DIFFERENT SAMPLES OF MILK FOR PRESENCE OF CASEIN A File Report submitted to :
______________ ______________ Internal Examiner
______________ _______________ Head Of Chemistry Department Principal
CERTIFICATE This is to certify that this dissertation titled “Analysis of different samples of milk for presence of Casein” was submitted by Patit Pawan
Barik to Head of Chemistry Department of Kendriya Vidyalaya, Chittaranjan, W.B. carried under guidance and supervision during the Academic year 2013-2014.
ACKNOWLEDGE MENT I wish to express my deep gratitude and sincere thanks to the Principal, Kendriya Vidyalaya, Chittaranjan, W.B. for his encouragement and for all the facilities that he provided for this project work. I sincerely appreciate this magnanimity by taking me into his fold for which I shall remain indebted to him. I extend my hearty thanks to Mr. K.Batabyal (PGT Chemistry), who guided me to the successful completion of this project. I take this opportunity to express my deep sense of gratitude for his invaluable guidance, constant encouragement, constructive comments, sympathetic attitude and immense motivation, which has sustained my efforts at all stages of this project work.
DECLARATION I do hereby declare that this project work has been originally carried under the guidance and supervision of Mr. K. Batabyal (PGT Chemistry), Head of Chemistry Department, Kendriya Vidyalaya, Chittaranjan, W.B.
Patit Pawan Barik XII ‘A‛ Roll no.- 32
TABLE OF CONTENTS Introduction
Aim
Requirement
Theory
Procedure
Observations
Conclusion
Reference
INTRODUCTION Milk is a food of exceptional interest. Not only is milk an excellent food for the very young, but humans have also adapted milk, specifically cow‛s milk, as a food substance for
adapted milk, specifically cow‛s milk, as a food substance for persons of all ages. Many specialised milk products like cheese, curd, butter and ice cream are staples of our diet. Milk is probably the most nutritionally-complete food that can be found in nature. This property is important for milk, since it is the only food young mammals consume in the nutritionally significant weeks following birth. Whole milk contains Vitamins (principally Thiamine, Riboflavin, Pantothenic acid, and Vitamins A, D, and K), Minerals (Calcium, Potassium, Sodium, Phosphorus, and trace metals), proteins (which include all the essential amino acids), carbohydrates (chiefly Lactose), and Lipids (fats). The only important elements in which milk is seriously deficient are iron and Vitamin C. Infants are usually born with a storage supply of iron large enough to meet their needs for several weeks. Vitamin-C is easily secured through an orange juice supplement. Milk is the largest and the single most important commodity within the livestock sector. Although slightly varies in composition and properties, the milk of different species contain the same constituents in general. On average, milk is made up of 87.4% water and 12.6% milk solids (3.7% fat, 8.9% milk solids-not-fat). The milk solids-not-fat contain protein (3.4%), lactose (4.8%), and minerals (0.7%). Milk fat often called “butter fat” is commercially, the most valuable constituent of milk. It is also of great importance from the standpoint of the food value of the milk. The agreeable flavour of rich milk and to a large extent of other dairy products is largely due to the milk fat. Proteins are among the most complex of organic substances. They contain carbon, hydrogen, oxygen, nitrogen, sulphur and sometimes phosphorus. The protein of milk is not a single compound but includes two major proteins and small quantities of others. Between them casein constitute about 80 % of the total and lacto albumin 18%. A third protein recognized as present in milk is lacto globulin. It is present in very small amounts, probably about 0.05 to 0.07 %. Ash constituents of milk are extremely important in their relation to the heat stability of the milk.
Previous Experimental Observations &
Results OBSERVATIONS Average Percentage Composition of Milk from Various Mammals:
Source of milk
Water(%)
Minerals(%)
Proteins(%)
Fats(%)
Carbohydrates (%)
Cow
87.1
0.7
3.4
3.9
4.9
Human
87.4
0.2
1.4
4.0
4.9
Goat
87.0
0.7
3.3
4.2
4.8
Sheep
82.6
0.9
5.5
6.5
4.5
RESULTS The Buffalo‛s milk has highest casein presence in all the samples of milk. Therefore, buffalo‛s milk is most suitable for nutrition.
CASEIN Casein is a phosphoprotein, which has phosphate groups are attached to some of the amino acid side chains. Casein exists in milk as the calcium salt, calcium caseinate. This salt has a complex structure. It is composed of α, β, and κ caseins which form a micelle, or a solubilized unit. Neither the α nor the β casein is soluble in milk, singly or in combination. If κ casein is added to either one, or to a combination of the two, however, the result is a casein complex that is soluble owing to the formation of the micelle. The κ casein is thought to stabilize the micelle. Since both α and β casein are phosphoproteins, they are precipitated by calcium ions. The κ casein protein, however, has fewer phosphate groups and a high content of carbohydrate bound to it. It is also thought to have all its serine and threonine residues (which have hydroxyl groups), as well as its bound carbohydrates,
on only one side of its outer surfaces. This portion of its outer surface is easily solubilized in water since these polar groups are present. The other portion of its surface binds well to the water-insoluble α and β caseins and solubilizes them by forming a protective colloid or micelle around them. Since the entire outer surface of the micelle can be solubilized in water, the unit is solubilized as a whole, thus bringing the α and β caseins, as well as κ casein, into solution. Calcium caseinate has its isoelectric (neutrality) point at pH 4.6. Therefore, it is insoluble in solutions of pH less than 4.6. The pH of milk is about 6.6; therefore casein has a negative charge at this pH and is solubilized as a salt. If acid is added to milk, the negative charges on the outer surface of the micelle are neutralized (the phosphate groups are protonated) and the neutral protein precipitates: Ca2+Caseinate + 2 HCl ─› Casein + CaCl2 The calcium ions remain in solution. When milk sours, lactic acid is produced by bacterial action and the consequent lowering of the pH causes the same clotting reaction. The isolation of casein from milk will be carried out in this experiment. The casein in milk can also be clotted by the action of an enzyme called rennin. Rennin is found in the fourth stomach of young calves. However, both the nature of the clot and the mechanism of clotting differ when rennin is used. The clot formed using rennin, calcium paracaseinate, contains calcium. Ca2+Caseinate + Rennin ─› Ca2+Paracaseinate + A Small Peptide Rennin is a hydrolytic enzyme (peptidase) and acts specifically to cleave peptide bonds between phenylalanine and methionine residues. It attacks the κ casein, breaking the peptide chain so as to release a small segment of it. This destroys the water-solubilizing surface of the κ casein, which protects the inner α and β caseins and causes the entire micelle to precipitate as calcium paracaseinate. Milk can be decalcified by treatment with oxalate ion, which forms an insoluble calcium salt. If the calcium ions are removed from milk, a clot will not be formed when the milk is treated with rennin.
The clot, or curd, formed by the action of rennin is sold commercially as cottage cheese. The liquid remaining is called the whey. The curd can also be used in producing various types of cheese. It is washed, pressed to remove any excess whey, and chopped. After this treatment, it is melted, hardened and ground. The ground curd is then salted, pressed into molds, and set aside to age .It is a major protein constituent in milk & is a mixed phosphorprotein. Casein has isoelectric pH of about 4.7 and can be easily separated around this isoelectric pH. It readily dissolves in dilute acids and alkalies. Casein is present in milk as Calcium Caseinate in the form of “micelles”. These micelles have negative charge and on adding acid to milk the negative charges are neutralized. Natural milk is an opaque white fluid secreted by the mammary glands of female mammal. The main constituents of natural milk are Protein, Carbohydrate, Minerals, Vitamins, Fats and Water and are a complete balanced diet. Fresh milk is sweetish in taste. However, when it is kept for long time at a temperature of 5º it become sour because of bacteria present in air. These bacteria convert lactose of milk into lactic acid which is sour in taste. In acidic condition casein of milk starts separating out as a precipitate. When the acidity in milk is sufficient and temperature is around 36º, it forms semi-solid mass, called curd.
AIM To study the quantity of Casein in different samples of milk.
REQUIREMENTS Beakers (250 ml) Filter-paper Glass rod Weight box Filtration flask
Filtration flask Buchner funnel Test tubes Porcelain dish Different samples of milk 1 % Acetic acid solution
Ammonium sulphate solution
CHEMICAL REACTION Ca2+Caseinate2- + 2 CH3COOH(aq) ─› Casein + (CH3COO)2Ca
THEORY Casein is a phosphoprotein, which has phosphate groups are attached to some of the amino acid side chains. These are attached mainly to the hydroxyl groups of the serine and threonine moieties. Actually, casein is a mixture of at least three similar proteins, which differ primarily in molecular weight and amount of phosphorus they contain (number of phosphate groups). Casein exists in milk as the calcium salt, calcium caseinate. This salt has a complex structure. It is composed of α, β, and κ caseins which form a micelle, or a solubilized unit. Neither the α nor the β casein is soluble in milk, singly or in combination. If κ casein is added to either one, or to a combination of the two, however, the result is a casein complex that is soluble owing to the formation of the micelle. The κ casein is thought to stabilize the micelle. Since both α and β casein are phosphoproteins, they are precipitated by Calcium ions. The κ casein protein, however, has fewer phosphate groups and a high content of carbohydrate bound to it. It is also thought to have all its serine and threonine residues (which have hydroxyl groups), as well as its bound carbohydrates,
on only one side of its outer surfaces. This portion of its outer surface is easily solubilized in water since these polar groups are present. The other portion of its surface binds well to the water-insoluble α and β caseins and solubilizes them by forming a protective colloid or micelle around them. Since the entire outer surface of the micelle can be solubilized in water, the unit is solubilized as a whole, thus bringing the α and β caseins, as well as κ casein, into solution. Calcium caseinate has its isoelectric (neutrality) point at pH 4.6. Therefore, it is insoluble in solutions of pH less than 4.6. The pH of milk is about 6.6; therefore casein has a negative charge at this pH and is solubilized as a salt. If acid is added to milk, the negative charges on the outer surface of the micelle are neutralized (the phosphate groups are protonated) and the neutral protein precipitates: Ca2+Caseinate + 2 HCl ─› Casein + CaCl2 The calcium ions remain in solution. When milk sours, lactic acid is produced by bacterial action and the consequent lowering of the pH causes the same clotting reaction. The isolation of casein from milk will be carried out in this experiment. The casein in milk can also be clotted by the action of an enzyme called rennin. Rennin is found in the fourth stomach of young calves. However, both the nature of the clot and the mechanism of clotting differ when rennin is used. The clot formed using rennin, calcium paracaseinate, contains calcium. Ca2+Caseinate + Rennin ─› Ca2+Paracaseinate + A Small Peptide Rennin is a hydrolytic enzyme (peptidase) and acts specifically to cleave peptide bonds between phenylalanine and methionine residues. It attacks the κ casein, breaking the peptide chain so as to release a small segment of it. This destroys the water-solubilizing surface of the κ casein, which protects the inner α and β caseins and causes the entire micelle to precipitate as calcium paracaseinate. Milk can be decalcified by treatment with oxalate ion, which forms an insoluble calcium salt. If the calcium ions are removed from milk, a clot will not be formed when the milk is treated with rennin.
The clot, or curd, formed by the action of rennin is sold commercially as cottage cheese. The liquid remaining is called the whey. The curd can also be used in producing various types of cheese. It is washed, pressed to remove any excess whey, and chopped. After this treatment, it is melted, hardened and ground. The ground curd is then salted, pressed into molds, and set aside to age .It is a major protein constituent in milk & is a mixed phosphorprotein. Casein has isoelectric pH of about 4.7 and can be easily separated around this isoelectric pH. It readily dissolves in dilute acids and alkalies. Casein is present in milk as Calcium Caseinate in the form of “micelles”. These micelles have negative charge and on adding acid to milk the negative charges are neutralized.
PROCEDURE 1. A clean dry beaker has been taken, followed by putting 20 ml of cow‛s milk into it and adding 20 ml of saturated ammonium sulphate solution slowly and with stirring. Fat along with Casein was precipitate out. 2. The solution was filtered and transferred the precipitates in another beaker. Added about 30 ml of water to the precipitate. Only Casein dissolves in water forming milky solution leaving fat undissolved. 3. The milky solution was heated to about 40oC and add 1% acetic acid solution drop-wise, when casein got precipitated. 4. Filtered the precipitate, washed with water and the precipitate was allowed to dry. 5. Weighed the dry solid mass in a previously weighed watch glass. 6. The experiment was repeated with other samples of milk.
OBSERVATIONS According to above experiment : Sl. No.
Source of Milk
Weight of Dried Solid Mass
CONCLUSION The __________ milk has highest value of the dried solid mass i.e. the composition of Casein is highest in the sample of ________ milk.
SOLUTION TO THE ANALYSIS The ________ milk has the highest presence of casein in milk. Therefore, ________ milk is the best for nutrition.
REFERENCES Wikipedia Encyclopedia – Encarta Britannica icbse.nic.in Practical Chemistry books
This is the project created by me in Class 12th for the external practical exam. Read more » Posted by Patit Pawan Barik at 18:46
No comments:
Recommend this on Google
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