Carbohydrate Assay Lab Report
By
Jose Lorenzo C. Barbasa
11B – The Palm
December 12, 2018
General Biology 1
Ms. Carolina Q. Vicente, instructor/teacher
Purpose or Question:
How are we able to determine the type of carbohydrates present in the foods
we eat?
Background:
When we eat, we take in a certain amount of carbohydrates. As Grade 11
students, we are left with the question of whether these are monosaccharides,
disaccharides, polysaccharides, or even oligosaccharides. Yes, you may say we can
identify the type of carbohydrate it has just by looking it up on the World Wide Web.
But let’s have a case in point. How are we able to identify them using scientific
methods? Luckily, there are two tests we can use, and these are the Benedict’s
qualitative assessment (Benedict’s solution) and the Lugol’s iodine test. These
are chemical tests that manifest a change in colour to display the positivity or
negativity of a certain type of carbohydrate being tested.
The Benedict’s solution is a reagent often used in assessing for
monosaccharidal positivity or negativity (reducing sugars/simple carbohydrates). It is
blue in colour and transparent in visibility. When mixed with a monosaccharide
solution, it displays a change in colour, and may range from green to yellow to
orange to as far as brick-red.
Meanwhile, Lugol’s iodine is used to test for disaccharidal or polysaccharidal
positivity or negativity (complex carbohydrates). It is amber or brown in colour and
slightly translucent in visibility. When mixed with a disaccharide or polysaccharide, it
yields colours depending on what sugar is put. For example, if starch is present, it
gives a blue-black colour. If glycogen is present, it gives a brown-blue colour.
This activity involves making two chemical tests. In the first test, Benedict’s
solution will be used to test known sugars. In the second test, Lugol’s iodine will be
used to test an identical set of samples for starch. The final tubes will become the
control tubes or the basis tubes of the experiment.
Hypothesis:
The colour of the liquids will change to a certain extent, from lighter hues to
darker hues, and vice versa.
Materials:
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6 test tubes
test tube rack
test tube holder
wax pencil/tape
syringe/dropper
safety goggles and apron
Benedict’s solution
Lugol’s iodine solution
Paper towels
Samples (3 knowns and 5 unknowns)
Hot bath (beaker half filled with water and boiled)
Solutions
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Monosaccharide (glucose solution)
Disaccharide (table sugar solution)
Polysaccharide (corn starch solution)
biscuit solution
milk
juice (lemon/mint)
unknown
banana puree
potato puree
known