Biochemistry Chapter: Disaccharides and Fermentation

Disaccharides and Fermentation

• Disaccharides, like sucrose and lactose, need to be broken down into monosaccharides before fermentation can occur.
• This breakdown happens through hydrolysis, where a water molecule is added to the disaccharide.
• Sucrose hydrolysis produces glucose and fructose.
• Lactose hydrolysis produces glucose and galactose.
• Enzymes sucrase and lactase act as catalysts for sucrose and lactose hydrolysis, respectively.

Monosaccharide Fermentation

• Monosaccharides like glucose, fructose, and galactose all have the molecular formula C6H12O6.
• These monosaccharides ferment using yeast to produce ethanol and carbon dioxide.

Solubility Test

• Oil is miscible in chloroform but immiscible in ethanol and water.
• This follows the principle of "like dissolves like," where substances with similar polarities are more likely to mix.

Grease-Spot Test

• Water is absorbed by paper, while oil forms a translucent spot.

Acrolein Test

• Indicates the presence of glycerol, a component of fats and oils.
• Glycerol is dehydrated to form acrolein (acrylic aldehyde) with a characteristic burned copra odor when heated with KHSO4 (catalyst).

Sterol Test

• Sterols are hydroxyl derivatives of steroids (cyclopentanoperhydrophenanthrene).

Molish Test

• Detects carbohydrates by forming a violet ring when an acidic solution reacts with carbohydrates.
• This color is due to the interaction of the aldehyde with alpha-naphthol.
• Glucose, maltose, and starch all test positive for this reaction.

Benedict's Test

• Detects reducing sugars like glucose, fructose, and maltose.
• It uses copper(II) sulfate (CuSO4) which is reduced to red copper(I) oxide (Cu2O) by aldehydes, oxidizing them to carboxylic acids.
• The copper(I) oxide forms a brick red precipitate.
• Glucose, fructose, and galactose all test positive for this reaction.

Osazone Formation

• When a reducing sugar is heated with phenylhydrazine, a yellow precipitate called osazones is formed.
• Osazones are used to compare the structures of sugars due to their unique crystalline forms.
• The osazones of monosaccharides (glucose & fructose) form quickly and have similar needle-shaped crystals under the microscope.
• Disaccharides (maltose & lactose) form osazones more slowly and have distinct crystal shapes under the microscope.

Hydrolysis of Starch and Glycogen

• Iodine test for polysaccharides: iodine dissolved in an aqueous solution of potassium iodide (IKI) reacts with starch producing a deep blue-black color.
• Starch and glycogen both react with IKI to produce blue-black color.
• The degree of blue-black color is also dependent on the length of the chains of the polysaccharide molecules.

Fermentation of Sugars

• Sugar fermentation using yeast results in the production of ethanol and carbon dioxide.
• The fermentation of sucrose produces 4 molecules of ethanol and 4 molecules of carbon dioxide.
• Lactose is also C12H22O11 but the atoms are arranged differently.