biochemistry pre test lab experiment 4 Flashcards
memorize
3 kinds of proteins in milk
casein, lactalbumin, lactoglobulin
What is the most nutritionally complete food found in nature
milk
_______ is the main protein in milk. It is a phosphoprotein
casein
3 similar proteins in milk
β-casein, α-casein, κ-casein
__-casein and __-casein are both insoluble in water
β-casein, α-casein
__-casein is responsible for solubilizing the other two casein in water by promoting the formation of micelles.
κ-casein
Casein exists in milk as the calcium salt, _________ ________
calcium caseinate
Calcium caseinate has an isoelectric point of pH ____.
4.6
The pH of milk is about ____
6.6
second most abundant protein in milk is __________
lactalbumin
________ carries out the immunological properties of milk. They protect the younger mammal until its immune system has developed
lactoglobulins
EXTRACTION OF CASEIN:
1. Measure 30 mL of nonfat milk and place it in a 100-mL beaker. Add 30 mL of distilled water. Heat on a hot plate to about 1___°C (top of the hot plate at about 2___°C). Monitor the temperature of the milk using a thermometer.
1- 55°C, 2- 65°C
EXTRACTION OF CASEIN:
2. When the mixture has reached 55°C, add the ____ ______ _____ dropwise to the warm
milk with stirring using a glass rod. Do not add the acid too rapidly. Continue the acid
addition, keep the beaker on the hot plate until the liquid changes from milky to
almost clear, and the casein no longer separates (No more than 2 mL of the acid is
needed).
10% acetic acid
EXTRACTION OF CASEIN:
3. Stand the mixture for __ minutes.
5
EXTRACTION OF CASEIN:
4. Stir the precipitated casein until it forms a large ___________ ______; then remove it with a stirring rod or tongs (or by filtration) and place it in another beaker. Label the beaker “casein”.
amorphous mass
EXTRACTION OF CASEIN:
5. Keep the filtrate (______ _______) for PART III.
whey solution
EXTRACTION OF CASEIN:
6. Place the obtained casein in a 100 mL beaker and add 5 mL of a mixture of : _____ _____ and ________. Stir the casein in the mixture for a few minutes, decant the liquid, and repeat the process with a second 5 mL portion of the solvent. These washings remove any small quantities of fat that may have precipitated with the casein. Place the casein between several layers of filter paper to help dry the product, and let it stand in the air for 10-15 minutes.
1- 1:1 ethyl ether, 2- ethanol
- Divide the extracted casein into two. Place one portion in an Erlenmeyer flask with ___ mL of _______ and ____ mL of ___ ______, stopper the mixture, shake it to ensure solution of as much of the casein as possible, and save it for use in the chemical tests below. The other portion is for observation of its physical properties. Record the physical appearance of casein in Table 1.
35 mL of water and 0.5 mL of 1M NaOH
The 1______ Test is a general test for the presence of proteins, which is dependent on the presence of peptide bonds.
Buiret Test, Piotrowskis test
A positive result for the Buiret Test or Piotrowskis test
Violet color, if it contains peptides, proteoses, and peptones, a minimum of 2 peptide bonds
reagents of the biuret test
CuSO4 and NaOH
_______ test is a general test for the presence of proteins, which is dependent on the presence of free alpha amino groups.
Ninhydrin test
reagents of the Ninhydrin test
0.1 Ninhydrin solution
A positive result for the Ninhydrin test
Presence of diketohydrin, a color complex that is also known as Ruhemans purple. (Deep blue or violet color)
The __________ test is used to indicate the presence of amino acids containing phenyl (benzene ring), namely phenylalanine, tyrosine, and tryptophan
Xanthoproteic test
reagents of the Xanthoproteic test
HNO3 and ammonia NH3
A positive result for the Xanthoproteic test
(Yellow to orange color)
________ reaction is a specific test for the presence of the amino acid tryptophan
Adamkiewicz reaction
A positive result for the Adamkiewicz reaction
Formation of violet ring
___________ test is a general test for the presence of carbohydrates in a solution
molisch’s test
reagents of the molisch’s test
Molishs reagent and sulfuric acid (concentrated H2SO4)
_________ test is a test for phosphate in the solution.
Phosphate test
reagents of the Phosphate test
Concentrated HNO3 and 0.2M ammonium molybdate
Tests for characterization of protein
Biuret Test, Ninhydrin Test, Xanthoproteic test, Adamkiewicz Test, Molischs test, and Phosphate test
Test for other nutrients in milk
Test for lactose, test for calcium, Test for chlorides, and test for sulfates
reagents of the Test for lactose
Benedicts reagent
A positive result for the Test for lactose
Formation of a brick-red precipitate
reagents of the test for calcium
Potassium Oxalate (K2C2O4)
A positive result for the test for calcium
A white precipitate of calcium oxalate (CaC2O4)
reagents of the test Test for chlorides
Silver Nitrate (AgNO3)
A positive result for the Test for chlorides
A white precipitate of silver chloride (AgCl)
reagents of the test Test for sulfates
Barium Chloride (BaCl2)
A positive result for the Test for sulfates
A white precipitate of barium sulfate (BaSO4)
