Carbohydrate Digestion

• food in the mouth is broken down by teeth, giving a large surface area 
• saliva containing amylase is realeased from the salivary glands 
• this hydrolyses the glycosidic bonds in starch and forms maltose 
• the stomach pH (acidic) then denatures the amylase enzyme 
• more amylase is realeased from the pancreas
• in the small intestine maltase is realeased from the epithelial lining
• this hydrolyses the maltose into alpha gluclose 

Sucrase: 

• the epithelial lining of the small intestine releases sucrase 
• this hydrolyses the glycosidic bond in sucrose 
• this forms the monosaccharides glucose and fructose 

Lactase: 

• the epithelial lining of the small intestine releases lactase 
• this hydrolyses the glycosidic bond in lactose
• this forms the monosaccharides glucose and galactose 

• Monosaccharides are the basic molecules carbohydrates and proteins are made of 
• Carbohydrates and proteins are polymers

The structure of alpha glucose is: 

• alpha glucose is linked by glycosidic bonds formed by condensation to make maltose and starch

• the production of lactase reduces in adult life 
• in some people it reduces too much and they may not produce any at all 
• this means they do not produce enough lactase to digest lactose 
• when undigested lactose reaches the large intestine it is broken down by microorganisms 
• this creates a large volume of gas, leading to nausea, diarrhoea and cramps 
• it is not life threatening but can lead to insufficient calcium in the diet 

Benedicts Test; for reducing sugars: 

• add Benedicts reagent (copper sulphate) to a food sample in liquid form 
• heat the mixture in boiling water for 5 minutes 
• if the solution turns orange, then there is a reducing sugar present 

and non-reducing sugars: 

• if the sloution does not turn orange there is no reducing sugar present 
• add the food sample to hydrochloric acid and place back in the water bath for 5 minutes 
• then add sodium hydrogencarbonate to neutralise the acid 
• re test the solution with Benedicts reagent in a water bath for 5 minutes 
• if a non reducing sugar was present the solution will now turn orange 

Iodine Test: 

• easy to detect
• can be doen in a test tube or in a spotting tile 
• add two drops of iodine solution to the food sample 
• the presence of starch is indicated by the iodine turning black/blue