L5. Saccharides properties

1. Introduction
Saccharides are organic molecules consisting of C, H and O atoms. They area divided in three groups:
-Monosaccharides: formed by a linear carbon chain, are the building blocks of oligo and polysaccharides. They have a one functional group: cetone (C=O) or aldehyde (COH). Pentoses and hexoses can switch from acyciclic to cyclic forms called furanoses and pyranoses.
-Oligosaccharides: small polymer containing between 2 and 10 monoscharides.
-Polysaccharides: big polymers with more than 10 monosaccharides.

These molecules perform numerous roles in living organisms like storage of energy, structural components...

Saccharides yields 4'2 kcal/gr and are abundant in fruits, sweets, honey, beans, tubers, rice, pastas and cerelas. They are a common source of energy in living organisms.

2.Objectives
1-Identify different sugars from its properties.
2-Differentiate mono and disaccharides.
3-Understand the relation between structure and some properties.

3. Materials
-Test tube rack
-10 mL Pipet
-Distilled water
-5 test tubes
-1 dropper
-5 spatula
-Lactose
-Maltose
-Glucose
-Sucrose
-Starch
-Lugol's iodine
-Distilled water

4. Procedure
1- In the first part of the experiment we are going to test some physical properties of the saccharides you have in the lab : flavour, crystal structures and colour. How?
a) Flavour: Put a small amount of each saccharide in your hand and taste it! Is it sweet or not sweet?
b) Crystals: Observe a small amount of each saccharide on a clock glass under magnification.
c) Colour: white, transparent or creamy.

To test solubility:
2-Clean and dry 5 test tubes and label them "G,M,L,SU,S"
3-Put 5 mL of water in each test tube
4-With the aid of a spatula, put a small amount of each saccharide inside the labelled test tube and test if they are soluble or insoluble.
5-Observe if each saccharide forms a mixture called dissolution or a colloidal suspension.

Lugol's iodine test:
(the test you make to comprove if something contains starch)
6-Finally, add 2 drops of Lugol's iodine to each test tube and test if the reaction is positive or negative. Lugol's is a solution of elemental iodine (I) and potassium iodine (KI) in water that is use to test a saccharide. The reaction is positive when iodine reacts by turning from yellow to a purple, dark-blue/black colour.

Finally we are going to test if some foods contain starch. Try with potato!
1-Add 2 or 3 drops of Lugol's solution to one piece of potato and observe whats is happening.

5. Questions
1-Write the empirical formula of each saccharide that you have use. Classify each one in mono,oligo or polisaccharide.
2-Wich are aldoses and wich are cetoses?

Glucose: C6H12O6 monosaccharid (aldo)
Maltose: C12H22O11 disaccharid (aldo)
Sucrose: C12H22O11 disaccharid (ceto)
Lactose: C12H22O11+H2O disaccharid (aldo)
Starch: C6H12O5 polisaccharid (aldo)

3-Wich of the bond links monosaccharides? Oliglicosidic
4-Wich saccharide/s is/are sweet? Is this property related to the structure of the molecule?
Starch is the only one that isn't sweet, because it is polysaccharide.
5-Wich saccharide/s is /are insoluble?  Is this property related to the structure of the molecule?
Starch isn't soluble because it is a very big molecule with high weight
6-Qich saccharide has reacted with Lugol's iodine solution? Starch
7-Wich kind of food contains starch? Flawr, cereals, pasta, rice...
8- Calculate the energy from the nutrition facts label from a cereal:
a)Calculate the energy that comes from the saccharides.
23g saccharides · 4'2 kcal/gr = 96,6 kcal
b)Wich % of the total energy comes from the saccharides?