Everything Life Sciences Grade 10

FACT

Meat or vegetables:
which is a better
source of protein?
Both animal protein
and protein from
vegetables is good
for health. But each
type comes with
other nutrients. So
which ’package’ of
nutrients-meat or
vegetables is better
for health?

• A 180 gram
  steak
  provides 40
  g of protein
  BUT also
  provides 38
  g of fat
  which is
  more than
  the Recom-
  mended
  Dietary
  Allowance


• The same
  amount of
  salmon gives
  34 g of
  protein and
  18 g of fat.


• A cup of
  cooked
  lentils has 18
  g of protein
  and 1 g of
  fat.
  Therefore when
  choosing
  protein-rich foods,
  pay attention to
  what comes along
  with protein.
  Vegetable sources
  of proteins such as
  beans, nuts and
  whole grain are
  excellent choices
  and they offer
  healthy fibre,
  vitamins and

Figure 2.16: Child suffering from kwash-

iorkor

Figure 2.17: Child suffering from maras-

mus

Test for proteins

TheBiuret Testfor proteins using involves testing for the presence of the peptide bond.

Biuret reagent is a copper-based reagent that turns purple when bound to protein in an

alkaline solution (Figure 2.18). The more peptide bonds present, the greater the intensity of

the purple colour, indicating a higher protein concentration.

The presence of protein can also be detected usingMillon’s reagent. Millon’s reagent re-

acts with tyrosine amino acids, common to most proteins, and results in the formation of a

reddish-brown precipitate when heated.

Table 2.4 below summarises the major tests and their expected results in the presence and

absence of protein.

Test reagent Positive

result

Negative

result

Biuret

reagent

Violet/purple

colour

Blue colour

Millon’s

reagent

Red-brown

colour

White

colour

Table 2.4: Observable colour changes when testing for the presence of protein.

Investigation: Test for the presence of proteins

Aim:

To use the Biuret test as well as Millon’s reagent to test for the presence of proteins

Apparatus:

40 2.4. Organic compounds