Digestion and Lactose Intolerance

• Most carbohydrates are polymers
• Contain elements Carbon, Hydrogen and Oxygen
• Carbohydrates are made from Monosaccharides:

Formula for Glucose, Galactose and Fructose --- C₆H₁₂O₆

• Glucose is a hexose sugar (6-Carbon) - this goes onto make larger chains such as Cellulose and Starch
• Alpha and beta forms of Glucose

This is an alpha-glucose structure:

Two monosaccharides join together to form a disaccharide.

• Glucose + Fructose --> Sucrose

(sucrose is just regular table sugar) + hydrolysed down again by Sucrase

• Glucose + Galactose ---> Lactose

(lactose is the sugar in Milk - you can be intolerant to it) + hydrolysed by Lactase

• Glucose + Glucose --> Maltose

(Maltose is a product of starch digestion, broken down by the enzyme amylase)

+ hydrolysed to its monosaccharides again by maltase

• You are lactose intolerant if you don't make enough of the enzyme Lactase
• Lactase hydrolyses Lactose into its monosaccharides - glucose and galactose
• Undigested lactose is fermented by bacteria in the large intestine and can go onto cause intestinal complaints such as...

- Stomach cramps

- Excessive flatuence due to large volume of gas

- Diarrhoea

... And obviously these are really unpleasant! So, before lactose-intolerant people drink milk, you can add lactase to it to pre-digest it for you.

• Lactose intolerance is bad for babies because their source of food is milk, so they need special Formula milk to be made for them.

Test for reducing sugars: Reducing sugars = monosaccharides & some dissaccharides such as Maltose.

• You add Benedict's Reagent - Copper (II) sulfate which is blue
• You heat the sample
• If the sample contains reducing sugars such as glucose, galactose, fructose or maltose then the solution should turn brick red. (a red precipitate forms)

Test for non-reducing sugars:

• You boil the solution in dilute HCL (Hydrochloric Acid) and then neutralise with sodium hydrogencarbonate.
• You then do the Benedict's Test for the reducing sugars which would now have been hydrolysed into their constituent monosaccharides
• Then the same result- but compared with another sample of the same with just the reducing sugar test one on its own - so you can prove that it is non-reducing sugars.

Starch is made up of a mixture of two polysaccharide types - amylose and amylopectin

• Both are long chains of alpha-glucose
• Linked by glycosidic bonds
• Formed in condensation reactions

Starch-> Salivary Amylase and Pancreatic Amylase break it down into maltose

Maltase (from the intestinal epithelium) then breaks down maltose into alpha-glucose molecules

The test for Starch uses iodine dissolved in potassium iodide solution.

When starch is present:

Brown-orange changes to Blue-Black colour.