Carbohydrate Structure CARBOHYDRATES ARE THE MOST ABUNDANT CLASS OF COMPOUNDS IN THE BIOLOGICAL WORLD. IT CONSTITUTES 50% OF THE DRY MASS OF THE EARTH - PowerPoint PPT Presentation

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Carbohydrate Structure CARBOHYDRATES ARE THE MOST ABUNDANT CLASS OF COMPOUNDS IN THE BIOLOGICAL WORLD. IT CONSTITUTES 50% OF THE DRY MASS OF THE EARTH

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carbohydrate structure carbohydrates are the most abundant class of compounds in the biological world. it constitutes 50% of the dry mass of the earth s biomass. – PowerPoint PPT presentation

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Title: Carbohydrate Structure CARBOHYDRATES ARE THE MOST ABUNDANT CLASS OF COMPOUNDS IN THE BIOLOGICAL WORLD. IT CONSTITUTES 50% OF THE DRY MASS OF THE EARTH


1
Carbohydrate Structure CARBOHYDRATES ARE THE
MOST ABUNDANT CLASS OF COMPOUNDS IN THE
BIOLOGICAL WORLD. IT CONSTITUTES 50 OF THE DRY
MASS OF THE EARTHS BIOMASS.
MOST IMPORTANT CONSTITUENT OF ALL LIVING
ORGANISMS. STRUCTURAL COMPONENTS OF CELLS AND
RECOGNITION SITES ON CELL SURFACES.
ROOTS, FRUITS, STEM, SEEDS AND LEAVES CONTAIN
CARBOHYDRATE. Plants use them for their own
metabolic need and serve the metabolic need of
animals.
2
Carbohydrates
  • Cx(H2O)y
  • 70-80 human energy needs (US50)
  • gt90 dry matter of plants
  • Monomers and polymers
  • Functional properties
  • Sweetness
  • Chemical reactivity
  • Polymer functionality

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
Functional group
Ketone Aldehyde
4 Tetrose Tetrulose
5 Pentose Pentulose
6 Hexose Hexulose
7 Heptose Heptulose
8 Octose Octulose
Number of carbons
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

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
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
9
D-Hexosulose Isomers
10
D-Hexosulose Isomerization
Figure 5
11
Ring Formation
Anomeric carbon
Figure 7
12
Anomeric Structures
13
Acyclic and Cyclic Glucose
a-D-glucopyranose
a-D-glucofuranose
38 in solution
62 in solution
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
  • 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
  • Ascorbic acid browning
  • (Lipid)
  • Polymers lead to color Small molecules to flavor

25
Caramelization
  • Heat to 200C
  • 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
  • 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
  • Pentosegthexosegtdisaccharidegtgtpolysaccharide
  • protein concentration (free amines)
  • Inhibited by acid
  • amines are protonated
  • and used up, pH drops
  • Sulfur dioxide
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