Formal Report No. 1
Experiment Nos. 1, 2, & 3
Isolation, hydrolysis and characterization of casein from non-fat milk and
protein analysis using Bradford method
Abigail Ruth Velasquez a * and Robert Bryan Yee
aDepartment of Chemistry, College of Science, University of Sto. Tomas,, España Blvd. Sampaloc, Manila and 1015, Philippines
1. Introduction Proteins are important components of all organisms.
Proteins can also be called as polypeptides since these
molecules have more than 50 amino acids. The amino
acids are linked together by a bond called peptide bond
(McKee & McKee, 2004).
Proteins are classified according to their shape, size,
function, solubility & physical properties (Chatterjea,
2004). Proteins can also perform different functions
including metabolic regulation, transportation, for defense,
catalysis, and also as structural materials (McKee &
According to M. N. Chatterjea (2004), the general
properties of proteins include:
Proteins are tasteless in general. However, hydrolytic proteins have bitter taste.
Ideally, proteins are odorless but when heated, they give off a burning feather odor.
Proteins have large molecular weight.
The viscosity of proteins varies on what kind and shape of protein, and its concentration in the
Proteins can act as both acid and base because its side chain can have either a carboxylic acid or an
amine. Hence, they have an amphoteric behavior.
Proteins also have a tendency to form a precipitate from various ions.
Some proteins form an insoluble coagulum.
In the book written by Donald and Judith Voet and
Charlotte Pratt, different factors affect protein's stability. These factors include:
pH. Proteins are stable only at certain pH. Biological materials are dissolved in buffer
solutions at a specific pH range. If the pH used is
below or above the required pH, the protein
would undergo denaturation.
Temperature. There are different thermal stabilities for proteins. Some would denature at
low temperatures, while most proteins denature
at high temperatures.
ART ICLE INFO AB ST R ACT
Article history: Received August 11, 2014
Casein is a protein found in milk which has amino acids that are linked
together by peptide bonds. Casein from non-fat milk was isolated and
hydrolyzed using isoelectric precipitation. Its isolate and hydrolyzate were
characterized using five different color reaction tests. Bradford method was
used to determine the concentration of the unknown protein solution. It can be
concluded that casein was isolated from the non-fat milk based on the
different color reaction tests done. There is a 62.14% percent yield. The mean
concentration of the unknown protein solutions is 159.2μg/mL and has a percent error of 6.13%.
Biuret Test Bradford Method
Ninhydrin Test Proteins
Presence of degradative...