Foodchem Lecture 16
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What is the general formula for a carbohydrate?
What is the basic unit of a carbohydrate?
Simple sugar or monosaccharide
What does the name 'simple sugar' mean?
Will not undergo acid hydrolysis to form smaller units
What are 2 common examples for simple sugars?
D-glucose and D-fructose
Both glucose and fructose also exist as which other structure of compounds?
What is the definition of a dissacharide?
2 simple sugars linked by a covalent glycosidic bond
What is a covalent glycosidic bond?
A specific type of ther linkage (R-O-R) between the OH on the anomeric carbon of a sugar to any other alcohol (usually another sugar molecule)
Where does sucrose come from?
What is sucrose made up of?
Glucose and fructose
What is lactose made up of?
Glucose and galactose
Where does maltose come from?
Starch enzymatic hydrolysis
What is maltose made up of?
2 glucose molecules
What is the definition of an oligosaccharide?
3-10 monosaccharides linked together
What is raffinose made up of?
Trisaccharide of galactose, glucose and fructose
What is stachyose made up of?
A tetrassacharide of glucose, fructose, and galactose
What is a common use of oligosaccharides?
Used as prebiotics, or promoters of desirable intestinal flora
What are 2 examples of prebiotics?
- Oligofructose (2-8) units
- Inulin (9-64) units
What are polysaccharides?
- Longer chain length polymers, found in nature
- A variety have food applications
What are some examples of polysaccharides?
- Xanthan gum
What is the role of carbohydrates in nature?
- Energy sources as starch for germination of seeds
- Structural components as cellulose and hemicellulose in plants (including trees)
- Ready supply of energy as mono and disaccharides
- Short term supply of energy in muscles (as glycogen)
What are mono and disaccharides used for in food functionality?
- Sweetening agents
- Coloring agents (caramel color)
- Viscosity enhancers
- Flavor production (caramellization, Maillard rxn)
- Flavor carriers (plated flavors, like vanilla on sugar)
What are oligosaccharides used for in food functionality?
What are polysaccharides used for in food fuctionality?
- Thickening and/or gelling agents
- Emulsion stabilizers
- Water holding/binding agents
- Production of edible films
- Encapsulation of flavors
How are carbon chains numbered in sugars?
From the carbonyl end down
The C3 to C7 portions of monosaccharides are known as what?
What is the carbonyl group of a monosaccharide?
An aldehyde or ketone
What is the simplest monosaccharide?
What is the absolute reference to determine D or L configuration of sugars?
Why was glyceraldehyde chosen to be the reference compound for determining D and L configuration?
- It has only one chiral carbon
- Most sugars have more than 1 chiral carbon
- The D or L designation of sugars is based solely on the configuration of the n-1 carbon, i.e. on the carbon one before last, when counting from the carbonyl group
What are enantiomers?
Mirror images, or any D vs. L configuration of the same sugar
What are epimers?
- Changes at any carbon other than the n-1 carbon, for example for the same molecular formula
- (As at C2 in D glucose vs D mannose)
- All epimers are considered different sugars
How are monosaccharides classified?
May be classified as to chain length and functional group type
What are ketoses?
6C ketones, like fructose
What are aldohexoses?
6C aldehydes, like glucose
How are monosaccharides generally represented for simplicity?
- As linear molecules
- In reality (both in crystals and, predominantly, in solution) they are cyclic
What do sugars form to become cycles?
Hemiacetals and hemiketals
How does the chair form of beta glucose form?
- The double bond oxygen becomes an alcohol
- The alcohol oxygen becomes an ether
- C1 becomes the center of a hemiacetal (A carbon wtih both an ether and alcohol on the same carbon)
How is cycle closure catalyzed?
By an acid
What is the anomeric carbon?
The new chiral carbon formed at C1 where the cycle closes
What are the alpha and beta forms of monosaccharides called?
What happens when a monosaccharide is dissolved in solution?
A dynamic equilibrium is set up between the 3 possible forms of the monosaccharide (open chain, alpha anomer, beta anomer)
What is mutarotation?
Changes in optical rotation, when a pure type of sugar is dissolved in water
What does mutarotation result from?
- the opening of one form, coming to equilibrium with the opposite anomer via the open chain form
- it may crystallize into the 5 member ring or into the 6 member ring
What is the breakdown of glucose equilibria?
- 62% alpha pyranose
- 37% beta byranose
- <1% open chain
What is fructos mutarotation like?
A 5 member ring (furanose)
In general, 6 carbon aldoses tend to form which cyclic rings in mutarotation?
In general, 6 carbon ketoses tend to form which cyclic rings in mutarotation?
The crystalline form of simple sugars is always what?
The aldehyde group on aldose is a strong agent for what?
All monosaccharides are which kinds of sugars?
What is a reducing sugar?
Capable of reducing metal ions and being oxidized to carboxylic acids (redox reaction)
What does Fehling's reagent react with?
Only reacts with free aldehyde groups (showing presence of reducing sugars)
Why is fructose considered a reducing sugar?
- Fructose is a ketose, thus no free aldehyde group
- Still considered a reducing sugar since it goes through a rearrangement when in basic conditions (enolization)
How is reducing power of a sugar lost?
- If the OH on the anomeric C is covalently bound to another group
- The glycosidic link is formed, and the cycle cannot open up anymore, thus no free aldehyde can be regenerated
Is sucrose a reducing sugar?
NO - due to its glycosidic bond, where both anomeric carbons are tied up in making the bond
Is maltose a reducing sugar?
Is lactose a reducing sugar?
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