Food tests
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All monosaccharides and some disaccharides are
reducing sugars
The two disaccharides that are reducing sugars
Maltose and lactose
An OH group on carbon 1 of the monosaccharide / disaccharide means
It’s a reducing sugar
Test for reducing sugar
Add benedict’s solution and see if it changes colour Heat to 80 degrees
Results for reducing sugar
Blue - No sugar Green - Trace Yellow - Low Orange - Moderate Brick red - High
Reducing sugar test results are ….
Semi-quantitative (Results vary on how much sugar there is)
Test for Non-reducing sugars
Add dilute hydrochloric acid Heat in water bath Neutralise using an alkali Add excess beneficts raegant and heat to 80
Two methods of finding the quantitative results of the amount of reducing sugar
• Filter solution and weigh precipitate • Remove precipitate and use colorimeter to measure absorbency of remaining benedict’s solution
• Test for starch
Add iondine (brown) If starch is present it will turn (Blue/black) Brown to blue and black B-B
Test for protein
Add biurets raegant (pale blue) If protein is present it will turn purple Results are semi-quantitative so the darker the purple the more protein
How can you identify amino acids in a mixture
Use chromatography to separate them by the amino acids polarity
Test for lipids
Add ethanol and water and shake Milky emulsion means lipid is present