Biochemical tests using Benedict’s reagent for reducing sugars and non-reducing sugars. Iodine/potassium iodide solution for starch.

Add Benedicts solution to the sample and heat:

• If it turns orange it is a reducing sugar
• If its blue then do the following:

Add hydrochloric acid and heat for a further 5 minutes, after this add hydrogen carbonate to neutralise it. Now repeat the process from the begining of the test and add benedicts solution and then heat:

• If it turns orange then it is a non-reducing sugar
• If it stays blue then it is not a sugar at all.

Acid is added to hydrolyse the non-reducing sugars breaking them down into monomers- reducing sugars.
The solution is neutralised as acid would prevent the Benedicts test from working.

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To test for starch pipette a couple of drops of iodine on to the sample you are testing.

• If it stays red then there is no starch
• If it goes blue/black then there is starch.

Biological molecules such as carbohydrates and proteins are often polymers and are based on a small number of chemical elements. Monosaccharides are the basic molecular units (monomers) of which carbohydrates are composed. The structure of a-glucose as... and the linking of a-glucose by glycosidic bonds formed by condensation to form maltose and starch.

Carbohydrates are biological molecules (this means they are produced by living things) they contain Carbon, Hydrogen and Oxygen. They have the empirical formula CH20.

Carbohydrates are often polymers made up of monomers; polysaccharides made up of monosaccharides.

Glucose is a monosaccharide, it is a hexose- which means it contains 6 carbons- so its molecular formula is C6H12O6. There are other hexose which will be made up of the same components, but they are different molecules due to their structure, the structure of alpha-glucose is:

Structure of alpha-glucose

Two monosaccharides join together by a condensation reaction, to make a disaccharide; when more are joined it becomes a polysaccharide. In the condensation reaction between two glucose molecules, a glycosidic bond is formed (bond between the two sugars) creating a disaccharide and water:

Products of a condensation reaction between two glucoses

Two glucoses are joined they form the disaccharide maltose. Many glucoses joined together form the polysaccharide starch,

Starch, the role of salivary and pancreatic amylases and of maltase located in the intestinal epithelium; disaccharides, sucrase and lactase; Sucrose is a disaccharide formed by condensation of glucose and fructose. Lactose is a disaccharide formed by condensation of glucose and galactose. Lactose intolerance.

Starch is a polysaccharide, it is broken down by the body into monosaccharides, in two stages:

• Amylase (released from the salivary and pancreatic glands) breaks starch down into maltose,
• Maltase (found in the intestines) breaks maltose down into glucose.

Sucrose is a disaccharide, it is digested in to two monosaccharides:

• Sucrase breaks sucrose down into glucose and fructose.

Lactose is a disaccharide, it is digested in to two monosaccharides:

• Lactase breaks lactose down into glucose and galactose.

Some peoples bodies do not produce enough lactase, this means there will be undigested lactase in their digestive system (after eating a product containing this sugar, like milk.) This lactase is fermented by bacteria which produces methane. The symptom of this is painful wind and the name of this condition is lactose intolerance.

Having lactose in the intestine decreases the water potential, this causes water to move in by osmosis, diluting the faeces and giving diarrhoea to the sufferer.