biochemical food tests

food test for reducing sugars

• mix food sample with Benedict’s reagent

• food sample will turn from light blue to brick red ONLY if reducing sugars are present in sample

food test for non-reducing sugars

• add hydrochloric acid to food sample (this hydrolyses glycosidic bonds)

• add sodium hydrogen carbonate to neutralise

• add Benedict’s reagent and then boil

• if sample positive colour will change from light blue to brick red

food test for starch

• mix sample with Iodine solution

• if sample changes colour from orange/brown to blue/black, starch is present

food tests for lipids

• lipid sample must be mixed with an equal volume of absolute ethanol, this dissolves the lipid

• add an equal volume of water and gently shake

• if lipids are present in sample, result will be white and cloudy emulsion

food test for proteins

• must add Biuret reagent to food sample send gently shake

• if proteins are present colour will change from light blue to purple