LABORATORY 2

FOOD SCIENCE SBK3033

LAB 2: PROTEIN ANALYSIS

MAUREEN SANTIH ANAK AMBANG	D20141067070
SHARIFAH AWANIS BINTI SYED MOHD ASWAD	D20141067053
MOHAMAD HARITH BIN SULAIMAN	D20141067083

DATE OF EXPERIMENT: 28 FEBRUARY 2017

LECTURER: ASSOCIATE PROFESSOR DR HASIMAH ALIMON

Part 1: Test for protein

Results:

	Substance	Reaction with copper sulphate and sodium hydroxide
1.	1% starch solution	Solution remains blue
2.	10% glucose solution	Solution remains blue
3.	1% albumen solution	Solution turns from blue to violet
4.	water	Solution remains blue

Discussions:
     The subunits which make up proteins are amino acids. The amino acids are joined together by dehydration synthesis to forms chains, which are hundreds of amino acids long which is called proteins. Proteins function as enzymes or as structural units in cells. They do most of the work in a cell. Almost all of the exciting stuff such as metabolism, memory, hormone action, and movement involves proteins. In this lab, we have learnt method of measuring protein presence which is biuret test.  

       The reaction gives a purple colour only for albumen. Sodium hydroxide and copper sulphate produce purple colour whether proteins are present or not. The reaction is inhibited with the presence of glucose or starch. Proteins are not present in the starch, glucose and water. Proteins are present in albumen only.

         Biuret solution is a blue liquid that changes to purple when proteins are present and to pink in the presence of short chains of polypeptides. The copper atom of the biuret solution reacts with the peptide bonds to cause the color change. The Biuret Test often used to determine the presence of peptide bonds in protein. As a student you will most likely be testing for the presence of protein in foods.

Part 2: enzymatic coagulation of the casein from milk with rennet and Part 3: Coagulation of protein from soymilk using a salt (magnesium sulphate).

Results:

	Weight of milk	Weight of curd	Describe the curd
Milk + acid	121.7 g	20 g	White, fine granules
Milk + rennet	101.312 g	47.12 g	White, fluffy, thick
Soymilk + Epsom salt	236.74 g	49.1 g	Light brown, fine granules

Questions:

1.Compare the weights of the curds from the milk (acid and rennet) with that from the soymilk.
   The weight of soymilk and Epsom salt is the most, the weight of milk and rennet less and the weight of milk and acid is least. The weight of milk with acid and milk with rennet are the less compared to the weight of soymilk and Epsom salt because no coagulation occur.

2.Why did the casein that was coagulated with the rennet weigh more than the casein that was precipitated with the acid?
   The casein that was coagulating with the rennet weighs more than casein that was precipitated with the acid because the rennet coagulum contains milk protein and fat, while the acid precipitate contains only casein.

3.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?
   The amount of acid casein precipitated from the whole milk is less compared to the amount of soy protein coagulated from the soymilk. From the Nutritional Facts label for 250ml of milk contain 7.5 g of protein where for 250 ml of soymilk contain only 5.8 g of protein. Therefore the results of the curds produced are not equivalent with the labels.

4.  How did the biuret test indicate the presence of proteins?

The biuret test indicates the presence of proteins by changing the colour to purple-violet. It is used to test for the presence of peptide bond. The Biuret reagent contains copper ions which give it a blue color.

Conclusion:

All the food product that contain protein can be tested with biuret reagent that contain copper ions that give blue colour and it will show positive results as copper solution will turn from blue to violet colour to indicate the present of protein.