Experiment 6 milk analysis

EXPERIMENT 6 TITLE : ANALYSIS OF MILK

INTRODUCTION : The basic composition of milk remains the same regardless of its sources. Milk is primarily water. About 87.4% of milk is water, 3.3% protein, 3.3% fat, 4.7% carbohydrate and 0.7 % ash. There are many types of milks on the market, including: Full cream – full cream milk contains around four per cent fat and is a source of vitamins A and D. For children up to the age of two years, full cream milk is recommended. Reduced fat – expect around half as much fat in reduced fat milk as full cream. Children over the age of two years can drink reduced fat milk. Skim milk – contains less than one per cent fat. Children older than five years can safely consume skim milk. Both reduced fat and skim milk have vitamin A and D added to replace the naturally occurring vitamins that are reduced when the fat is removed. Calcium enriched – generally milks that are enriched with extra calcium are also fat reduced. A 250 ml glass of milk contains 408–500 mg of calcium. Flavoured – these milks can either be full cream or reduced fat. However, most varieties contain a lot of sugar. UHT (ultra-high temperature-treated) milk – is treated with very high heat to allow milk to be stored for long periods. Lactose is a type of carbohydrate or sugar that naturally occurs in milk from any mammal, including humans. Foods that contain lactose are better tolerated. Soy milk is both a lactoseand casein-low alternative for those with dairy allergies.

A. DETERMINATION OF Ph INTRODUCTION : An acid is a substance which dissociates to produce hydrogen ions in solution. A base (alkaline) is a substance which produces hydroxyl ions in solution. It can equally be stated that an acid is a substance which donates a proton and a base is a substance which accepts a proton. The symbol pH is used to denote acidity; it is inversely related to hydrogen ion concentration. When an acid is mixed with a base, neutralisation takes place; similarly a base will be neutralised by an acid. Cow's milk has a pH ranging from 6.4 to 6.8. Actually, milk has a pH of around 6.5 to 6.7, which makes it slightly acidic. Some sources cite milk as being neutral since it is so close to the neutral pH of 7.0. Milk contains lactic acid, which is a hydrogen donor or proton donor. Lactic acid is the normal bacteria present in milk and dairy products.

OBJECTIVES : To determine the pH of milk.

METHODS : 1. The pH meter was calibrated with buffer 4 and 7. 2. The milk was allowed to reach room temperature without cooking and re-pasteurising it. 3. The milk was poured into universal bottle. 4. The pH meter probe was inserted into the bottle of milk and the pH was recorded. 5. The pH of milk was recorded at 0 day, 1 day and 2 days. 6. The graph of pH versus day was plotted. DISCUSSION : In this experiment, we have learned the different pH of milk. We used whole milk and soymilk as a sample. Both of the milk was poured into universal bottle. Then, the pH meter probe was inserted into the bottle and the pH was recorded at 0 day, 1 day and 2 days. All the result was recorded in Table 6.1. After that, the graph of pH versus day was plotted. Refer Graph 1. As a result, pH of soymilk has a lower value than pH whole milk which is 5.33. By refer to the Graph 1, it shows that, the pH of both of it will decrease against the days. The longer the time, the lower the pH will obtain. If an acid is added to milk, or if acid-producing bacteria are allowed to grow in milk, the pH falls. As the pH drops due to lactic acid production by the bacteria in the milk, casein will precipitates. Hence milk curdles as it sours, or the casein precipitates more completely at low pH. When the pH of milk is changed, the acidic or basic groups of the proteins will be neutralised. At the pH at which the positive charge on a protein equals exactly the negative charge, the net total charge of the protein is zero. This pH is called the isoelectric point of the protein (pH 4.6 for casein).

B. DERMINATION OF CASEIN FROM MILK WITH AN ACID ( VINEGAR)

INTRODUCTION : The largest structures in the fluid portion of the milk are "casein" (roughly 79% of total milk protein). There are several different types of casein proteins: alpha-, beta-, kappa- and gamma- caseins. It is dispersed as calcium caseinate in the watery part of milk, which is

called the milk serum. An important characteristic of casein is its precipitation as a curd at pH of 4.6 or below which can be accomplished by action of renin or “rennet”. Milk contains dozens of other types of proteins beside the caseins including enzymes. These other proteins are more water-soluble than the caseins and do not form larger structures. Because they proteins remain suspended in the whey left behind when the caseins coagulate into curds, they are collectively known as whey proteins. Whey proteins make up approximately 18% of the protein in milk, by weight. Lactoglobulin is the most common whey protein by a large margin.

OBJECTIVES : To determine the coagulated casein from milk with adding an acid (vinegar) .

METHODS : 1. The pH meter was calibrated with buffer 4 and 7. 2. The empty beaker was weighed and the weight was recorded. 3. 120 mL of milk in the beaker was weighed and the weight was recorded in the data table ( weight of beaker with milk – weight of beaker = weight of milk ) 4. The pH of milk was measured. The thermometer was placed in the beaker. 5. The beaker with the milk was placed on a hot plate. The meat was heated to 70 C. The hot plate was turned off and the beaker was removed. 6. 11 mL of vinegar was added to the warm milk and it was stirred. Then the milk was allowed to sit for 10 minutes. The casein will precipitate into heavy white curds. The remaining liquid is the whey. 7. The pH of the liquid portion was measured again. 8.

Cheesecloth was cut out a piece (2-3 layers) large enough to cover the top and 2 inches down the sides of a beaker.

9. Using the rubber band over the top of the beaker to fasten the cheesecloth,. 10. The curdled milk was poured into the beaker, the curd (casein) was collecting in the cheesecloth and allowing the vinegar and whey to drain off into the bottom of the beaker. 11. The cheesecloth was gathered up with the casein and it was rinsed in cool water by dipping into another beaker containing water. 12. The casein was squeezed until almost dry and then the cheesecloth was spread out to let the casein dry for 5 minutes. 13. The precipitated was weighed and the results were recorded. The texture and the colour of the curd were recorded.

DISCUSSION : In this experiment, we have learned how to determine the coagulated casein from milk with adding an acid (vinegar). In this practical, we used whole milk and soymilk as a sample. Firstly, 11 mL of vinegar was added to the warm milk and it was stirred. After a while, the casein will precipitate into heavy white curds while the remaining liquid is the whey. The pH of the liquid portion was measured. Then, the curd (casein) was collecting in the cheesecloth . The casein was squeezed until almost dry and then the cheesecloth was spread out to let the casein dry. After that, the casein precipitated was weighed and all the results were recorded in Table 6.2 on Data Sheet. The result shows, the weight of casein in whole milk is higher than in soymilk, which is 32.8388. This is because, the texture of the casein we get for whole milk is solid and moist if compare with soymilk which is watery and wet. In general, it was subsequently shown that casein is made up of a number of fractions and is therefore heterogeneous. The whey proteins are also made up of a number of distinct proteins as shown in the scheme in Figure 1.

Figure 1

Casein is easily separated from milk, either by acid precipitation or by adding rennin. In cheese-making most of the casein is recovered with the milk fat. Casein is dispersed in milk in the form of micelles. The micelles are stabilised by the Κcasein. Caseins are hydrophobic but Κ-casein contains a hydrophilic portion known as the glycomacropeptide and it is this that stabilises the micelles. After the fat and casein have been removed from milk, one is left is whey, which contains the soluble milk salts, milk sugar and the remainder of the milk proteins. Like the proteins in eggs, whey proteins can be coagulated by heat. Whey is the liquid portion of milk, consisting primarily of 93% water, lactose and whey protein. High concentrated whey that is high in protein, but low in lactose and minerals. Soy milk has lower lactose than in whole milk. Thus, the low lactose in the soymilk, the concentration whey is lower. So the casein in the soymilk is lower.

CONCLUSION : In conclusion, we know how to analysis the milk by determine the different pH of milk and the coagulated casein from milk with adding an acid (vinegar). The sample we use in this experiment is whole milk and soymilk. With this sample, we need to determine which one has the ability to safe longer using pH and to determine the higher casein in milk. After the experiment the results show that whole milk has higher casein than soymilk because soymilk has lower lactose than in whole milk. Thus, the low lactose in the soymilk, the concentration whey is lower. So the casein in the soymilk is lower. pH of soymilk has a lower value than pH whole milk which is 5.33. The longer the time exposed, the lower the pH will obtain.

QUESTION : 1.

What causes the reduction in the pH of milk? The reduction pH of milk is because of an acid is added to milk, or acid-producing bacteria grow in milk.

2. Compare the amount of acid casein precipitated from the whole milk with the amount of soy protein coagulated from the soymilk. How do your results compare with the nutrition facts label for each product? __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________

3. List 3 factors that influence the precipitated of casein in milk? pH, bacteria and enzyme. 4. What is the importance of casein in the food industry? They are used to improve nutritive value, medical food, and palatability of imitation cheese.

REFFERENCES:

1. Brown. A. (2011). Understanding Food Principles and Preparation 4th edition. International edition. Milk (pp 211-219). 2. Murano. P. S. (2003). Understanding Food Science and Technology. International edition. Milk and dairy products (pp 41-45). 3. http://chemistry.about.com/od/foodchemistryfaqs/a/Is-Milk-An-Acid-OrA-Base.htm 4. http://www.ilri.org/InfoServ/Webpub/fulldocs/ilca_manual4/Milkchemistr y.htm 5. http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Milk_th e_facts_and_fallacies 6. http://en.wikipedia.org/wiki/Milk 7. http://www.ehow.com/about_5485584_lactosefree-milk-vs-soy-milk.html