carbohydrates Flashcards
(43 cards)
Classification by number of Monosaccharide units:
● Monosaccharides (1) - glucose, fructose, galactose (GFG)
● Disaccharides (2) - maltose, lactose, sucrose (MLS)
● Oligosaccharides (2-10) - raffinose, stachyose
● Polysaccharides (10 or more) - starch, glycogen, cellulose
Simplest sugar and cannot be hydrolyzed further
Monosaccharide
Classification by number of Carbon atoms:
● Pentoses: five carbon atoms
○ Aldopentoses: ribose and xylose
● Hexoses: six carbon atoms
○ Aldohexoses: glucose, galactose
○ Ketohexoses: fructose
Converts pentoses into furfural and hexoses into 5-hydroxymethylfurfural which then reacts with phenolic compounds
Dehydrating acids
Reducing sugars include aldoses containing either a free aldehyde group or a cyclic hemiacetal
Copper (II) ions containing solutions
Objective of Benedicts Test
To determine the presence or absence of reducing sugar in the solution.
● All monosaccharides are reducing sugars
● A reducing sugar has a free aldehyde group or a free ketone group
Sodium carbonate: _____ g
Sodium citrate: _____ g
Distilled water: _____ mL
Copper sulfate pentahydrate: _____ g
Sodium carbonate: 10g
Sodium citrate: 17.3g
Distilled water: 100 mL
Copper sulfate pentahydrate: 1.73g
Na carbonate: provides ________
Na citrate: forms ________
Na carbonate: provides alkaline medium
Na citrate: forms complexes with Cu^2+ ions
(Benedict’s Test) Interpretation of Result
● Blue - 0, negative/no sugar
● Green - 0.5-1%, traces of reducing sugar
● Yellow - 1-1.5%, low amount of reducing sugar
● Orange - 1.5-2%, moderate amount of reducing sugar
● Brick red - >2%, large amount of reducing sugar
(Benedict’s Test)
Positive color:
Variable color:
Positive color: brick red precipitate
Variable color: green (+/-)
Barfoed’s Test Objectives
used to detect the presence of reducing monosaccharides
distinguish reducing monosaccharides from disaccharides
(Barfoed’s Test) Interpretation of Result
● Positive Result: Brick red precipitate at the bottom of the tube.
● Monosaccharide + barfoed’s reagent = 5 minutes (brick red/red/brown precipitate)
● Disaccharide + barfoed’s reagent = 10 minutes (any color)
(Barfoed’s Test)
Positive color:
Barfoed’s reagent:
Positive color: brick red/brown
Barfoed’s reagent: copper sulfate & acetic acid
In Barfoed’s Test, Acetic acid - provides _______
condition that ________ pH
acidic, decreases
Seliwanoff’s Test Objective
● To detect the presence of ketohexoses in a given sample.
● To distinguish ketoses from aldoses.
Seliwanoff’s Test | Interpretation of Result
Ketose Color
Aldose Color
● Ketose reacts to produce a deep cherry red color
● Aldoses may react slightly to produce a faint pink to cherry red color if the test is prolonged.
In Seliwanoff’s Test, ______ and _______also give a positive result for this test as these are hydrolyzed by acid to give fructose.
Sucrose and Insulin
Bial’s Orcinol Test Objective
● To detect the presence of carbohydrates.
● To distinguish the pentoses and pentosans from other derivatives of carbohydrates like the hexoses.
Bial’s Test Interpretation of Result
Positive color:
Negative color:
Positive color: blue-green
Negative color: any color besides blue-green
The presence of a blue-green complex indicates the presence of _________ in the sample.
pentoses
Bial’s Solutions
5% fructose, 5% sucrose, 5% ribose, 5% glucose
Purpose of Mucic Acid Test
● Detects galactose and lactose in a
given sample.
● Distinguish galactose containing
saccharides and other sugars.
Each test’s objective
Benedict’s Test:
Barfoed’s Test:
Seliwanoff’s Test:
Bial’s Orcinol Test:
Benedict’s Test: amount of sugar
Barfoed’s Test: if monosaccharide or disaccharide
Seliwanoff’s Test: if aldose or ketose
Bial’s Orcinol Test: if pentose or hexose
What is Mucic Reagent and Nitric Acid
● Mucic Reagent is a concentrated
Nitric Acid.
● Nitric Acid causes the formation of
crystals in a solution.
