1.5 Carbohydrates: Tests Flashcards
The difference between reducing sugars and non-reducing sugars How to test for reducing sugars (Benedict's reagent) How to test for non-reducing sugars How to test for starch (iodine)
What are the two categories of sugars?
Reducing and non-reducing
What sugars are included in reducing sugars?
All monosaccharides and some disaccharides like maltose and lactose
What sugars are included in non-reducing sugars?
Some disaccharides like sucrose and all polysaccharides
How do you test for reducing sugars?
- Add Benedict’s reagent
- Heat in a water bath
- Red precipitate forms in a positive result
What is a positive result for reducing sugars?
A brick red precipitate
What does a blue solution indicate in a reducing sugar test?
No reducing sugar
What does a green solution indicate in a reducing sugar test?
Low concentration of reducing sugar
What does an orange solution indicate in a reducing sugar test?
Medium concentration of reducing sugar
What does a brick-red solution indicate in a reducing sugar test?
High concentration of reducing sugar
What are quantitative methods to determine reducing sugar concentration?
Colorimeter or weighing the precipitate
How do you test for non-reducing sugars?
(To be performed after a negative Benedict’s)
- Hydrolyse with hydrochloric acid
- Heat in a water bath
- Neutralise with an alkali
- Retest with Benedict’s
- Positive result is a red precipitate
What is a positive result for non-reducing sugars?
A brick red precipitate after hydrolysis
How do you test for starch?
Add iodine solution
What is a positive result for starch?
A blue-black solution
