L5. SACCHARIDES PROPERTIES

INTRODUCTION:

On monday, we lerned more about saccharides. This are organic molecules consisting of C, H and O atoms. And are divided in three groups:

- Monosaccharides: Formed by a linear carbon chain, are the building blocks of oligo and polisaccharides. They have a one functional group: cetone or aldehyde. Pentoses and hexoses can swith from acyciclic to cyclic forms called furanoses and pyranoses. Like fructose, glucose or galactose.

- Oligosaccharides: Small polymer containing between 2 and 10 monosaccharides. Like lactose, sucrose or maltose.

- Polysaccharides: big polymers with more tan 10 monosaccharides. Like starch, glycogen, cellulose and chitin.

This molecules give diferent functions in the organisms, energy (starch, glicogen), and structural components (cellulose, ribose, chitin and desoxiribose).

Saccharides yield 4,2 Kcal/gr and are abundant in fruits, sweets, honey... They are a common source of energy in living organisms.

Our objectives in thes case were identify different sugars from its properties, differentiate mono and disaccharides and understand the relation between structure and some properties. 

MATERIALS:

- Test tube rack

- 10mL pipet

- Distilled water

- 5 test tubes

- 1 dropper

- 5 spatula

- Clock glass

- Lactose

- Maltose

- Glucose

- Sucrose

- Starch

- Lugol's iodine

PROCEDURE:

	GLUCOSE (G)	MALTOSE (M)	SUCROSE (SU)	LACTOSE (L)	STARCH (S)
Flavour	Sweet	Sweet	Sweet	No sweet	No sweet
Crystaline form	Crystalline	No crystalline	Crystalline	No crystalline	No crystalline
Colour	White	White	White	White	Cream
Solubility	Soluble	Soluble	Soluble	Soluble	Insoluble
Lugol's iodine	-	-	-	-	+

In the first part of the experiment we tested some phisycal properties of the saccharides: flavour, cristal structure and colour. How?

1. Flavour: Put small amunt of each saccharide in your hand and taste it! it can be sweet or not.
2. Crystals: Observe a small amount of each saccharide on clock glass under magnification.
3. Colour: White, transparent or creamy.

To test solubility:

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

Lugol's iodine test:

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 a elemental iodine (I) and potassium iodine (KI) in water that is use to test a saccharide. The reaction is positive when iodine reactss by turning from yellow to purple, dark-blue/black colour.

RESULTS AND CONCLUSIONS:

We can see that lactose is a disaccharide that don't have sweet flavour. The starch have a cream colour, it's insoluble and it's positive with the Lugol's iodine test because is the only polysaccharide of the experiment. The rest of the saccharides are disaccharides. 

QUESTIONS:

1.- Write the empirical formula of each saccharide that you have use. Show structures of the five saccharides. Classify each one in one group: mono, oligo or polysaccharide.

G: C6H12O6 - monosaccharide.

M: C12H22O11 - oligosaccharide.

SU: C12H22O11 - oligosaccharide.

L: C12H22O11 - oligosaccharide.

S: C6H10O5 - polisaccharide.

2.- Which of the monosaccharides are aldoses and which are ketoses?

ALDOSES: glucose, maltose, lactose, starch.

KETOSES: sucrose.

3.- Which bond links monosaccharides?

Oligosaccharides.

4.- Which saccharide/s is/are sweet? Is this property related to the structure of the molecule?

Glucose, maltose, sucrose

5.- Which saccharide/s is/are soluble? Is this property related to the structure of the molecule?

Starch, It's a big molecule, it have a high molecular weight and is relacionated with the structure.

6.- Which saccharide has reacted with Lugol's iodine solution?

Starch

7.- Which kind of foods contains starch?

Cereals, pasta, rice, legums...                             

8.- Calculate the energy from the nutrition facts labelfrom a cereal

• Calculate the energy that comes from the saccharides.

23gr saccharides

4,2 Kcal => 1g

23x4,2= 96.6Kcal