1. Carbohydrate Structure
FDSC400

2. Carbohydrates Cx(H2O)y 70-80% human energy needs (US~50%)
>90% dry matter of plants
Monomers and polymers
Functional properties
Sweetness
Chemical reactivity
Polymer functionality
Structural simplicity denies the complex chemistry

3. Simple Sugars Cannot be broken down by mild acid hydrolysis
C3-9 (esp. 5 and 6)
Polyalcohols with aldehyde or ketone functional group
Many chiral compounds
C has tetrahedral bond angles

4. Nomenclature Ketone Aldehyde 4 Tetrose Tetrulose 5 Pentose Pentulose 6
Functional group
Ketone
Aldehyde 4
Tetrose
Tetrulose 5
Pentose
Pentulose 6
Hexose
Hexulose 7
Heptose
Heptulose 8
Octose
Octulose
Number of carbons
Number then –ose or -ulose
Table 1

5. Chiral Carbons A carbon is chiral if it has four different groups
Chiral compounds have the same composition but are not superimposable
Display in Fisher projection
Start with the simples possible sugar – 3 carbon acetaldehyde CHOCHOHCH2OH
Identify one chiral carbon
Determine there are two versions of this molecule with similar structures but different configurations
Fisher identified these structures and guessed on the conformation for the L-series and D-series
Fisher projection just like a cross
D-glyceraldehyde
L-glyceraldehyde
ENANTIOMERS

6. Glucose Fisher projection
D-series sugars are built on D-glyceraldehyde
3 additional chiral carbons
23 D-series hexosulose sugars (and 23 L-series based on L-glyceraldehyde)
C-1
C-2
C-3
C-4
Making more complex sugars is then just a case of adding C(H2O) into acetaldehyde
Creates many more chiral carbons so a whole series of molecules 2^n
We are mainly concerned with the D-series
C-5
C-6
Original D-glyceraldehyde carbon

7. D-Fructose A ketose sugar
One less chiral carbon than the corresponding aldose
Sweetest known sugar

8. The Rosanoff Projection
Simplified way of showing sugar structure

9. D-Hexosulose Isomers
Start with D-glyceraldehyde and add left or right facing OH

10. D-Hexosulose Isomerization
Catalyzed by pH or enzyme
Figure 5

11. Ring Formation Anomeric carbon Figure 7
Carbonyls can react with alcohols to form a hemiacetal
Creates two different anomeric forms
Anomeric carbon
Figure 7

12. Anomeric Structures

13. Acyclic and Cyclic Glucose
a-D-glucopyranose
a-D-glucofuranose
38% in solution
62% in solution
Much of the chemical reactivity of simple sugars is at the aldehyde group and while there isn’t much of it its important
~0.02% in solution
b-D-glucopyranose
b-D-glucofuranose
Figure 12

14. Ring Formation
Intramolecular reaction between alcohol and carbonyl to form a ring
6-membered rings are pyranose
5-membered are furanose
Generates a new a-carbon and two additional anomers (a- and b-)

15. Oxidation (or “What does it mean to be a reducing sugar”)
Aldehydes can be oxidized to corresponding carboxylic acids
Cu(II) Cu(I)
Use as a TEST

16. Reduction
Carbonyl groups can be reduced to alcohols (catalytic hydrogenation)
Sweet but slowly absorbed
Glucose is reduced to sorbitol (glucitol)
Xylose can be reduced to xylitol
Once reduced – less reactive; not absorbed

17. Esterification
An acid chloride or acid anhydride can add to an alcohol to form an ester
Frequent way to react with a fatty acids
A few subsituents to form a surfactants
6-8 to form OLESTRA
sugar

18. Dimerization
An alcohol can add to the alcohol of a hemiacetal (formed after ring formation) to form an acetal
Dehydration
Depending which conformation the hemiacetal is, the link can either be a- or b-, once link is formed it is fixed
-H2O

19. Example Simple Sugars Maltose
Malt sugar, enzymatic degradation product from starch
Mild sweetness characteristic flavor
Two glucose pyranose rings linked by an a-1-4 bond
Ring can open and close so a REDUCING SUGAR

20. Example Simple Sugars Sucrose Table sugar
a-glucopyranose and b-fructofuranose in an a, 1-1 link
The rings cannot open so NOT a reducing sugar
Easily hydrolyzed
Used to make caramels

21. Example Simple Sugars Lactose
~5% milk (~50% milk solids). Does not occur elsewhere
Glucose-galactose linked by 1-4 b glycosidic bond.
Galactose opens and closes so REDUCING sugar
Lactase deficiency leads to lactose intolerance. (More resistant than sucrose to acid hydrolysis).

22. Example Simple Sugars Trehalose
                            
Trehalose
Two glucose molecules with an a 1,1 linkage
Non reducing, mild sweetness, non-hygroscopic
Protection against dehydration

23. Browning Chemistry
What components are involved? What is the chemistry?
Are there any nutritional/safety concerns?
Are there any positive or negative quality concerns?
How can I use processing/ingredients to control it?

24. Types of Browning Enzymatic Caramelization Maillard (Lipid)
Ascorbic acid browning
(Lipid)
Polymers lead to color – Small molecules to flavor

25. Caramelization Heat to 200°C
35 min heating, 4% moisture loss
Sucrose dehydrated (isosacchrosan)
55 min heating, total 9% moisture loss
Sucrose dimerization and dehydration  caramelan
55 min heating. Total 14% moisture loss
Sucrose trimerization and dehydration  caramelen
More heating darker, larger polymers insolubilization
Flavor

26. Maillard Browning
“the sequence of events that begins with reaction of the amino group of amino acids with a glycosidic hydroxyl group of sugars; the sequence terminates with the formation of brown nitrogenous polymers or melanoidins”
John deMan

27. Maillard Browning Formation of an N-glucosamine Amadori Rearrangement
Esp LYSINE
Amadori Rearrangement
(Formation of diketosamine)
Degradation of Amadori Product
Mild sweet flavor
Condensation and polymerization
color

28. Involvement of Protein -Strecker Degradation-
Amine can add to dicarbonyl
Lysine particularly aggressive
Adduct breaks down to aldehyde
Nutty/meaty flavors
Nutritional loss

29. Nutritional Consequences
Lysine loss
Mutagenic/carcinogenic heterocyclics
Antioxidants

30. Control Steps Rapidly accelerated by temperature
Significant acceleration at intermediate water activities
Sugar type
Pentose>hexose>disaccharide>>polysaccharide
protein concentration (free amines)
Inhibited by acid
amines are protonated
and used up, pH drops
Sulfur dioxide