CASEIN AND SOURING OF MILK

There are three kinds of proteins in milk: casein, lactalbumins, and lactoglobulins. All three are globular proteins, which tend to fold back on themselves into compact, nearly spheroidal units and are more easily solubilizied in water as collodial suspensions than fibrous proteins are. They are “complete proteins”, so called because they contain all the amino acids essential for building blood and tissue, and they can sustain life and provide normal growth even if they are the only proteins, but they can contain greater amounts of amino acids than the proteins in egg and meat.

Casein, the main protein in milk, is a phosphoprotein. The phosphate groups are attached to the hydroxyl groups of some of the amino acid side chains. Casein exists in milk as the calcium salt, calcium caseinate. It is actually a mixture of at least three similar proteins which differ primarily in molecular weight and the amount of phosphorus groups they contain ( α, β and κ caseins), they form a micelle, or a solublized unit. Neither the α nor the β casein is soluble in milk and neither is soluble either 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.

  

Calcium caseinate has an isoelectric point of 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 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 casein micelles are neutralized (by protonation of the phosphate groups) and the neutral protein precipitates, with the calcium ions remaining in solution:

Ca-caseinate + 2H⁺  → casein + Ca²⁺

A natural example of this process occurse when milk sours. The souring of milk is an intricate process started by the action of microorganisms on the principal carbohydrate in milk, lactose. The microorganisms hydrolyse the lactose into glucose and galactose. Once galactose has been formed, lactobacilli, a strain of bacteria present in milk, convert it to the sour-tasting lactic acid. Since the production of the lactic acid also lowers the pH of the milk, the milk clots when it sours due to the precipitation of casein. The structure of lactic acid is shown below 

Many "cultured" milk products are manufactured by allowing milk to sour before it is processed. For instance, milk or cream is usually allowed to sour somewhat by lactic acid bacteria before it is churned  to make butter. The fluid left after the milk is churned is sour and is called buttermilk. Other cultured milk products include sour cream, yogurt, and certain types of cheese.

Isolation of Casein

WEIGHING OF MILK SAMPLES

ISOLATION OF CASEIN BY ADDING ACETIC ACID

SEPARATED CASEIN

BUCHNER FUNNEL

FILTRATION 

BIURET TEST

XANTHOPROTEIC TEST(AFTER ADDING NAOH)

XANTHOPROTEIC TEST

DRIED CASEIN SAMPLES 

CHEMISTRY PROJECT WORK,2012

REPORT OF A PROJECT WORK ON

ISOLATION OF CAESIN FROM DIFFERENT SAMPLES OF MILK AND ITS CHARACTERIZATION

SUBMITTED TO

The Department of Chemistry, Darrang College,

Tezpur-784001, Assam

 

For Partial Fulfillment of HS Final Year Chemistry Practical Examination 2012

SUBMITTED BY

NAME…………………………………………………………….

ROLL…………………… NO…………………………………..

                      REGISTRATION NO……………………….   OF ……………………………

                        SESSION……………………………………….

Under the Guidance of

Dr Palashmoni Saikia

Associate Professor, Department of Chemistry

Darrang College,Tezpur

Certificate

This is to certify that this dissertation titled “ISOLATION OF CASEIN FROM DIFFENET MILK SAMPLES AND ITS CHARACTERIZATION” submitted by Abagunthita Kashyap to th Department of Chemistry, Darrang College,Tezpur, was carried under my guidance and supervision during the academic year 2011-12.

Dr Palashmoni Saikia                                                                                                       Date:                                   

Associate Professor                                            

Department of Chemistry

ACKNOWLEDGEMENT

I am grateful to Almighty for giving me the inner strength and vision in my journey of life where this project work is no less a milestone.           

          First of all I thank my chemistry mentor MR. PRONIL BORA for his vital support, guidance and encouragement without which this project would not have come forth.

         A Special thanks to my teacher DR. PALASHMONI SAIKIA for his continuous support, advices and for giving useful suggestions and relevant ideas that facilitate an easy and early completion of this project

          I also express my gratitude our Lab Assistants SRI NIRANJAN DEKA, SRI PRANJAL BORAH, SRI PRATIM SAIKIA, SRI MANJUL BHUYAN AND RATUL BORAH for their willingness in providing us with necessary lab equipments and constant support without which this effort would have been worthless

          I am grateful to my parents and my brother whose blessing and wishes have gone a long way in the completion of this task

          Last but not the least I thank all my friends specially my best friend, without their prompt support my efforts would have been in vain  

                   Barasha Saharia                                                                         Dated:

 Preface

Milk is a complex biological mixture of chemicals that serves as the primary food source

for infant mammals. Milk contains most of the biological molecules necessary to sustain life including 

water, a variety of vitamins, minerals, proteins, sugars, and lipids (DNA, although necessary for life, is 

made by your body and therefore is not needed on a dietary level). Although most mammals stop 

drinking milk upon maturity, many (but not all) human cultures continue drinking milk and consuming 

milk products (for example, cheese, butter, and cream) throughout their entire life. 

It would be quite challenging to isolate every component of milk because some of the chemicals

are present in very small quantities. One can very easily, however, isolate the most abundant

components from each other. A common example of this 

is removing the fat from cow’s milk to make skim milk or 

removing the sugar from milk to make lactose‐free milk.

 The aim of this project is to isolate casein the most important protein present in milk. Through this work an attempt has been made to compare the percentage of casein present in cow,goat and buffalo milk. The isolated casein will be then characterized by biuret test and xanthoproteic test.

                                                        Content:

                                                                                                               Page No

1. Introduction

    1.1 Milk

    1.2 Composition of milk 

    1.3 Curdling of milk

    1.4 Butter and Cheese 

     1.5 Milk and health

2. Isolation of Casein

     2.1 Objective

    2.2 Methodology 

      2.3 Things required

      2.4 Procedure

      2.5 Yield

3. Characterization of casein

    3.1 Biuret test

    3.2 Xanthoproteic test

4. Conclusion

5. Reference

UGC SPONSORED NATIONAL SEMINAR ON RECENT CHALLENGES FOR CHEMICAL RESEARCH AND PRACTICES