Chapter 7 Notes

CHEM 2353
Fundamentals of Organic Chemistry

Chapter
Chapter

7 Carbohydrates

Organic and Biochemistry for Today (4th ed.)

Spencer L. Seager / Michael R. Slabaugh
Mr. Kevin A. Boudreaux
Angelo State University
www.angelo.edu/faculty/kboudrea
1

Carbohydrates and Biochemistry

• Carbohydrates are compounds of tremendous
biological importance:
– they provide energy through oxidation
– they supply carbon for the synthesis of cell
components
– they serve as a form of stored chemical energy
– they form part of the structures of some cells and
tissues
• Carbohydrates, along with lipids, proteins, nucleic
acids, and other compounds are known as
biomolecules because they are closely associated
with living organisms. Biochemistry is the study of
the chemistry of biomolecules and living organisms.
2
Chapter 7 Notes

Classification of
Carbohydrates

Carbohydrates
• Carbohydrates are polyhydroxy aldehydes or
ketones, or substances that yield such compounds on
hydrolysis
H O
C

H C OH

H C OH

H C OH

CH2OH
ribose The term “carbohydrate”
comes from the fact that
when you heat sugars, you
4
get carbon and water.
Chapter 7 Notes

Classes of Carbohydrates
• Monosaccharides contain a single polyhydroxy
aldehyde or ketone unit (saccharo is Greek for
“sugar”) (e.g., glucose, fructose).

• Disaccharides consist of two monosaccharide units

linked together by a covalent bond (e.g., sucrose).

• Oligosaccharides contain from 3 to 10

monosaccharide units (e.g., raffinose).

Classes of Carbohydrates
• Polysaccharides contain very long chains of
hundreds or thousands of monosaccharide units,
which may be either in straight or branched chains
(e.g., cellulose, glycogen, starch).

6
Chapter 7 Notes

The Stereochemistry
of Carbohydrates

Stereoisomers
• Glyceraldehyde, the simplest carbohydrate, exists in
two isomeric forms that are mirror images of each
other:
CHO CHO

HO C H H C OH

CH2OH CH2OH
L-glyceraldehyde D-glyceraldehyde

• These forms are stereoisomers of each other.

• Glyceraldehyde is a chiral molecule — it cannot be
superimposed on its mirror image. The two mirror-
image forms of glyceraldehyde are enantiomers of
each other.
8
Chapter 7 Notes

Chiral Carbons
• Chiral molecules have the same relationship to each
other that your left and right hands have when
reflected in a mirror.
• Achiral objects can be superimposed on the mirror
images — for example, drinking glasses, spheres,
and cubes.
• Any carbon atom which is connected to four
different groups will be chiral, and will have two
nonsuperimposable mirror images; it is a chiral
carbon or a center of chirality.
– if any of the two groups on the carbon are the
same, the carbon atom cannot be chiral.
• Many organic compounds, including carbohydrates,
contain more than one chiral carbon.
9

Examples: Chiral Carbon Atoms

• Identify the chiral carbon atoms (if any) in each of
the following molecules:
H Cl Cl Br

H C H H C H H C Cl H C Cl

H Cl Cl F
OH OH OH

CH3 C CH3 CH3 C CH2Cl CH3 C CH2CH3

H H H

O HO HO
O
CH3 C CH2CH3
10
Chapter 7 Notes

Examples: Chiral Carbons in Carbohydrates

• Identify the chiral carbons (if any) in the following
carbohydrates:
O H
C
CHO CH2OH
H C OH CH2OH
CH OH C O
HO C H O
H C OH OH
CH OH
H C OH
CH2OH H C OH OH OH
H C OH
erythrose CH2OH OH
CH2OH
glucose
11

2n Rule
• When a molecule has more than one chiral carbon,
each carbon can possibly be arranged in either the
right-hand or left-hand form, thus if there are n
chiral carbons, there are 2n possible stereoisomers.

Maximum number of possible stereoisomers = 2n

CH3

CH3

Cholesterol has 28 = 256

possible stereoisomers. (But
HO Nature makes only one!) 12
Chapter 7 Notes

Fischer Projections
• Fischer projections are a convenient way to
represent mirror images in two dimensions.
• Place the carbonyl group at or near the top and the
last achiral CH2OH at the bottom.
CHO CHO

HO C H H C OH

CH2OH CH2OH

CHO CHO

HO H H OH

CH2OH CH2OH
13
L-glyceraldehyde D-glyceraldehyde

Naming Stereoisomers
• When there is more than one chiral center in a
carbohydrate, look at the chiral carbon farthest from
the carbonyl group: if the hydroxy group points to
right when the carbonyl is “up” it is the D-isomer,
and when the hydroxy group points to the left, it is
the L-isomer.

CHO CHO

HO H H OH

HO H H OH

CH2OH CH2OH
L-erythrose D-erythrose

14
Chapter 7 Notes

Examples: Fischer Projections

• Draw Fischer projections
of D and L lactic acid: • Given the structure
for D-glucose, draw
CO2H the structure of L-
CH3 CH OH
glucose:
CHO

H OH

• Draw Fischer projections HO H

of D and L alanine:
H OH
NH2
CH3 CH CO2H H OH

CH2OH
D-glucose 15

Examples: Fischer Projections

• Identify the following compounds as D or L
isomers, and draw their mirror images.

CH2OH
CHO
C O
HO H
HO H
HO H
H OH
H OH
H OH
CH2OH
lyxose CH2OH
fructose

16
Chapter 7 Notes

What’s So Great About Chiral Molecules?

• Molecules which are enantiomers of each other have
exactly the same physical properties (melting point,
boiling point, index of refraction, etc.) but not their
interaction with polarized light.
• Polarized light vibrates only in one plane; it results
from passing light through a polarizing filter.

17

Optical Activity
• A levorotatory (–) substance rotates polarized light
to the left. [E.g., l-glucose; (-)-glucose]
• A dextrorotatory (+) substance rotates polarized
light to the right. [E.g., d-glucose; (+)-glucose]
• Molecules which rotate the plane of of polarized
light are optically active.
• Most biologically important molecules are chiral,
and hence are optically active. Often, living systems
contain only one of all of the possible
stereochemical forms of a compound. In some
cases, one form of a molecule is beneficial, and the
enantiomer is a poison (e.g., thalidomide).

18
Chapter 7 Notes

Monosaccharides

19

Classification of Monosaccharides
• The monosaccharides are the simplest of the
carbohydrates, since they contain only one
polyhydroxy aldehyde or ketone unit.
• Monosaccharides are classified according to the
number of carbon atoms they contain:
No. of Class of
carbons Monosaccharide
3 triose
4 tetrose
5 pentose
6 hexose

• The presence of an aldehyde is indicated by the

prefix aldo- and a ketone by the prefix keto-.
20
Chapter 7 Notes

Classification of Monosaccharides
• Thus, glucose is an aldohexose (aldehyde + 6 Cs)
and ribulose is a ketopentose (ketone + 5 Cs)
O H
C CH2OH
H C OH C O
HO C H H C OH
H C OH H C OH
H C OH CH2OH
CH2OH ribulose
a ketopentose
glucose
an aldohexose
21

Examples: Classifying Monosaccharides

• Classify the following monosaccharides:

CH2OH CHO
CH2OH CHO
C O HO H
C O HO H
H OH HO H
H OH HO H
HO H H OH
CH2OH CH2OH
CH2OH CH2OH

22
Chapter 7 Notes

The Family of D-aldoses

(L-forms not shown)
CHO
H OH Aldotriose
CH2OH 21 = 2
D-glyceraldehyde

CHO CHO
H OH HO H
Aldotetroses
H OH H OH 22 = 4
CH2OH CH2OH
D-erythrose D-threose

CHO CHO CHO CHO

H OH HO H H OH HO H
H OH H OH HO H HO H Aldopentoses
H OH H OH H OH H OH 23 = 8
CH2OH CH2OH CH2OH CH2OH
D-ribose D-arabinose D-xylose D-lyxose 23

The Family of D-aldoses

(L-forms not shown)

CHO CHO CHO CHO CHO

H OH HO H H OH HO H H OH

H OH H OH HO H HO H H OH
Aldohexoses
H OH H OH H OH H OH HO H 24 = 16
H OH H OH H OH H OH H OH

CH2OH CH2OH CH2OH CH2OH CH2OH

D-allose D-altrose D-glucose D-mannose D-gulose

CHO CHO CHO

HO H H OH HO H
H OH HO H HO H
HO H HO H HO H
H OH H OH H OH
CH2OH CH2OH CH2OH
D-idose D-galactose D-talose
24
Chapter 7 Notes

The Family of D-ketoses

(L-forms not shown)
CH2OH
O Ketotriose
CH2OH 20 = 1
Dihydroxyacetone

CH2OH
O
Ketotetroses
H OH 21 = 2
CH2OH
D-erythrulose

CH2OH CH2OH

O O

H OH HO H Ketopentoses
H OH H OH 22 = 4
CH2OH CH2OH
D-ribulose D-xylulose 25

The Family of D-ketoses

(L-forms not shown)

CH2OH CH2OH CH2OH CH2OH

O O O O

H OH HO H H OH HO H
Ketohexoses
HO H
H OH H OH HO H 23 = 8
H OH H OH H OH H OH

CH2OH CH2OH CH2OH CH2OH

D-Psicose D-Fructose D-Sorbose D-Tagatose

26
Chapter 7 Notes

Physical Properties of Monosaccharides

• Most monosaccharides have a sweet taste (fructose
is sweetest; 73% sweeter than sucrose).
• They are solids at room temperature.
• They are extremely soluble in water:
– Despite their high molecular weights, the
presence of large numbers of OH groups make
the monosaccharides much more water soluble
than most molecules of similar MW.
– Glucose can dissolve in minute amounts of water
to make a syrup (1 g / 1 ml H2O).

27

Physical Properties of Monosaccharides

Table 7.2 The relative sweetness of sugars
(sucrose = 1.00)

Sugar Relative Type

Sweetness
Lactose 0.16 Disaccharide
Galactose 0.22 Monosaccharide
Maltose 0.32 Disaccharide
Xylose 0.40 Monosaccharide
Glucose 0.74 Monosaccharide
Sucrose 1.00 Disaccharide
Invert sugar 1.30 Mixture of glucose and fructose
Fructose 1.73 Monosaccharide
28
Chapter 7 Notes

Chemical Properties of Monosaccharides

• Monosaccharides do not CH2OH
usually exist in solution in H
their “open-chain” forms: H
C O

an alcohol group can add H O

C
into the carbonyl group in OH H C
the same molecule to form HO
C C H
a pyranose ring containing
a stable cyclic hemiacetal H OH

or hemiketal. D-glucose
CH2OH CH2OH

H C O C O
OH H H
O C
H
C C
H
C
OH H OH H
HO H HO OH
C C C C

a pyranose ring H OH cyclic H OH

β-D-glucose hemiacetals α-D-glucose
29
β-up α-down

Glucose Anomers
O H
CH2OH C CH2OH
1
H C OH OH
O O
OH HO C H OH
1 1
H C OH
OH OH OH
H C OH
Haworth OH OH
structures CH2OH
α-D-glucose D-glucose β-D-glucose
36% 0.02% 64%

• In the pyranose form of glucose, carbon-1 is chiral,

and thus two stereoisomers are possible: one in
which the OH group points down (α-hydroxy group)
and one in which the OH group points up (β-
hydroxy group). These forms are anomers of each
other, and carbon-1 is called the anomeric carbon. 30
Chapter 7 Notes

Fructose Anomers
• Fructose closes on itself to form a furanose ring:
H
CH2OH O
O O
OH
CH2OH
a furanose ring

OH
D-fructose
β-hydroxy
CH2OH CH2OH CH2OH OH
O O
HO HO

OH α-hydroxy CH2OH
OH OH
α-D-fructose β-D-fructose 31

Drawing Furanose and Pyranose Rings

• Monosaccharides are often represented using the
Haworth structures shown below for furanose and
pyranose rings.
• The remaining OH groups on the ring point up or
down depending on the identity of the sugar.

always above ring

for D-saccharides
CH2OH
CH2OH
O O

Furanose Pyranose
ring ring
32
Chapter 7 Notes

Examples: Anomers
With Friends Like These, Who Needs Anomers?

• Identify the structures below as being the α- or β-

forms, and draw the structure of their anomers:

CH2OH OH CH2OH
O OH O
OH

OH
OH OH
ribose OH
galactose

33

Oxidation of Monosaccharides
• Aldehydes and ketones that have an OH group on
the carbon next to the carbonyl group react with a
basic solution of Cu2+ (Benedict’s reagent) to form
a red-orange precipitate of copper(I) oxide (Cu2O).
• Sugars that undergo this reaction are called
reducing sugars. (All of the monosaccharides are
reducing sugars.)

oxidation
Reducing sugar + Cu2+ product
+ Cu2O
deep blue red-orange
solution ppt

34
Chapter 7 Notes

Formation of Phosphate Esters

O
O
–
O P O CH2 –
O P O CH2 OH
– O
O O
OH O– HO

CH2OH
OH OH
OH
OH fructose 6-phosphate
glucose 6-phosphate
• Phosphate esters can form at the 6-carbon of
aldohexoses and aldoketoses.
• Phosphate esters of monosaccharides are found in
the sugar-phosphate backbone of DNA and RNA, in
ATP, and as intermediates in the metabolism of
carbohydrates in the body. 35

Glycoside Formation
• The hemiacetal and hemiketal forms
of monosaccharides can react with CH2OH
alcohols to form acetal and ketal
structures called glycosides. The O
new carbon-oxygen bond is called OH
the glycosidic linkage.
OH OCH3
CH2OH
OH
O methyl α-D-glycopyranoside
OH H+ +
+ CH3OH
CH2OH
OH OH OCH3
O
OH OH
α-D-glucose
OH
OH 36
methyl β-D-glycopyranoside
Chapter 7 Notes

Glycoside Formation
• Once the glycoside is formed, the ring can no longer
open up to the open-chain form. Glycosides,
therefore, are not reducing sugars.

Glycoside + Cu2+ NR

37

Examples: Glycoside Formation

• Identify the glycosidic linkage in each of the
following molecules:

CH2OH
CH2OH OCH3
OH
O O
OH
CH2OH
OCH2CH3
OH OH
OH

38
Chapter 7 Notes

Important Monosaccharides
CH2OH OH CH2OH OH
O O

OH OH OH
β-D-ribose CH2OH β-D-deoxyribose
Forms the sugar backbone of Forms the sugar backbone of
ribonucleic acid (RNA) OH O
OH deoxyribonucleic acid (DNA)
OH

OH
β-D-galactose
Incorporated with glucose
into lactose (milk sugar) 39

Important Monosaccharides
CH2OH CH2OH OH
O
OH
O HO
OH
CH2OH
OH OH
β-D-fructose
OH Also known as levulose and fruit
β-D-glucose sugar. Fructose is the sweetest of
Also known as dextrose and blood the monosaccharides. It is present
sugar; present in honey and fruits. in honey (1:1 ratio with glucose),
Glucose is metabolized in the body fruits, and corn syrup. It is often
for energy. Other sugars absorbed used to sweeten foods, since less
into the body must be converted to fructose is needed to achieve the
glucose by the liver. same degree of sweetness.

40
Chapter 7 Notes

Disaccharides

41

Disaccharides
• Two monosaccharides can be linked together
through a glycosidic linkage to form a disaccharide.

CH2OH CH2OH

O O
OH OH
+

OH OH OH OH
OH OH cyclic hemiacetal
α-D-glucose α-D-glucose

CH2OH CH2OH

O O
OH OH
+ H2O
O
OH OH
OH OH 42
α(1→4) glycosidic linkage Maltose
Chapter 7 Notes

Important Disaccharides
CH2OH
β(1→4) glycosidic linkage
O
CH2OH OH
OH
O O
CH2OH CH2OH OH OH
OH
O O α-D-glucose
OH OH β-D-galactose
O OH Lactose
OH OH Also known as milk sugar.
α-D-glucose OH α-D-glucose
OH Lactose constitutes 5% of cow's
Maltose milk and 7% of human milk. It is
Also known as malt sugar. It digested by the enzyme lactase.
is found in germinating grain
(such as barley), and is formed
during the hydrolysis of starch
to glucose during digestion.
Because it has a hemiacetal
group, it is a reducing sugar. 43

Important Disaccharides
CH2OH Sucrose
Also known as table sugar. Both anomeric
O α-D-glucose carbons of glucose and fructose are tied
OH together in the glycosidic linkage; thus neither
ring can open, and sucrose is not a reducing
α−1 → β−2 sugar. Sucrose is abundant in sugar cane
OH and sugar beets; maple syrup contains about
O glycosidic
CH2OH OH linkage 65% sucrose, with glucose and fructose
O present as well; caramel is the solid residue
β-D-fructose formed from heating sucrose. A flavoring
HO agent called invert sugar is produced by the
CH2OH hydrolysis of sucrose under acidic conditions,
which breaks it apart into glucose and
OH fructose; invert sugar is sweeter than sucrose
OH
because of the fructose. Some of the sugar
found in honey is formed in this fashion;
O
HO OH invert sugar is also produced in jams and
HO O OH jellies prepared from acid-containing fruits.
OH
O
OH
OH
44
Chapter 7 Notes

Oligosaccharides

45

Oligosaccharides
• Oligosaccharides contain from 3 to 10
monosaccharide units.

CH2OH
HOCH2
O O
CH2OH OH HO
OH O
O O
OH CH2OH
OH
OH β-D-fructose
α-D-glucose
β-D-galactose
OH Raffinose
An oligosaccharide found in peas and beans;
largely undigested until reaching the intestinal
flora in the large intestine, releasing hydrogen,
carbon dioxide, and methane)

46
Chapter 7 Notes

Polysaccharides

47

Polysaccharides
• Polysaccharides contain hundreds or thousands of
carbohydrate units.
• Polysaccharides are not reducing sugars, since the
anomeric carbons are connected through glycosidic
linkages.
• We will consider three kinds of polysaccharides, all
of which are polymers of glucose: starch, glycogen,
and cellulose.

48
Chapter 7 Notes

Starch
• Starch is a polymer consisting of D-glucose units.
• Starches (and other glucose polymers) are usually
insoluble in water because of the high molecular
weight, but they can form thick colloidal
suspensions with water.
• There are two forms of starch: amylose and
amylopectin.

49

Starch — Amylose
• Amylose consists of long, unbranched chains of
glucose (from 1000 to 2000 molecules) connected
by α(1→4) glycosidic linkages.
• 10%-20% of the starch in plants is in this form.
• Amylose forms helices (coils) which can trap
molecules of iodine, forming a characteristic deep
blue-purple color. (Iodine is often used as a test for
the presence of starch.)

CH2OH CH2OH CH2OH

O O O
OH OH OH
O O O O

OH OH OH
α(1→4) glycosidic linkage
50
Chapter 7 Notes

Starch — Amylopectin
• Amylopectin consists of long chains of glucose (up
to 105 molecules) connected by α(1→4) glycosidic
linkages, with α(1→6) branches every 24 to 30
glucose units along the chain.
• 80%-90% of the starch in plants is in this form.
CH2OH
O
OH
O α(1→6) branch point
O
OH
CH2OH CH2 CH2OH
O O O
OH OH OH
O O O O

OH OH OH 51
α(1→4) glycosidic linkage

Glycogen
• Glycogen, also known as animal starch, is
structurally similar to amylopectin, containing both
α(1→4) glycosidic linkages and α(1→6) branch
points.
• Glycogen is even more highly branched, however,
with branches occuring every 8 to 12 glucose units.
• Glycogen is abundant in the liver and muscles; on
hydrolysis it forms glucose, which maintains normal
blood sugar level and provides energy.

Amylose

Amylopectin/Glycogen

52
Chapter 7 Notes

Cellulose
• Cellulose is a polymer consisting of long,
unbranched chains of D-glucose connected by
β(1→4) glycosidic linkages; it may contain from
300 to 3000 glucose units in one molecule.

CH2OH
O
CH2OH OH
O O
O
CH2OH OH
OH
O O
β(1→4) glycosidic linkage
OH
OH
O

OH
53

Cellulose
• Because of the β-linkages, cellulose has a different
overall shape from amylose, forming extended
straight chains which hydrogen bond to each other,
resulting in a very rigid structure.
• Cellulose is an important structural polysaccharide,
and is the single most abundant organic compound
on earth. It is the material in plant cell walls that
provides strength and rigidity; wood is 50%
cellulose.
• Most animals lack the enzymes needed to digest
cellulose, although it does provide needed roughage
(dietary fiber) to stimulate contraction of the
intestines and thus help pass food along through the
digestive system.

54
Chapter 7 Notes

Cellulose
• Some animals, such as cows, sheep, and horses, can
process cellulose through the use of colonies of
bacteria in the digestive system which are capable of
breaking cellulose down to glucose; ruminants use a
series of stomachs to allow cellulose a longer time to
digest. Some other animals such as rabbits reprocess
digested food to allow more time for the breakdown
of cellulose to occur.
• Cellulose is also important industrially, from its
presence in wood, paper, cotton, cellophane, rayon,
linen, nitrocellulose (guncotton), photographic films
(cellulose acetate), etc.

55

Nitrocellulose, Celluloid, and Rayon

• Guncotton (German, schiessbaumwolle) is cotton which has been treated
with a mixture of nitric and sulfuric acids. It was discovered by Christian
Friedrich Schönbein in 1845, when he used his wife’s cotton apron to
wipe up a mixture of nitric and sulfuric acids in his kitchen, which
vanished in a flash of flame when it dried out over a fire. Schönbein
attempted to market it as a smokeless powder, but it combusted so readily
it was dangerous to handle. Eventually its use was replaced by cordite
(James Dewar and Frederick Abel, 1891), a mixture of nitrocellulose,
nitroglycerine, and petroleum jelly, which could to extruded into cords.
• Celluloid (John Hyatt, 1869) was the first synthetic plastic, made by
combining partially nitrated cellulose with alcohol and ether and adding
camphor to make it softer and more malleable. It was used in
manufacturing synthetic billiard balls (as a replacement for ivory),
photographic film, etc.; it was eventually replaced by less flammable
plastics.
• Rayon (Louis Marie Chardonnet, 1884) consists of partially nitrated
cellulose mixed with solvents and extruded through small holes, allowing
the solvent to evaporate; rayon was a sensation when introduced since it
was a good substitute for silk, but it was still highly flammable.

56
Chapter 7 Notes

How Sweet It Is!

Sugar Substitutes

57

Saccharin
O

NH
S

O O
Saccharin
The first of the artificial sweeteners, saccharin is noncaloric and
about 500 times sweeter than sugar. It was discovered in 1879
by Constantine Fahlberg, a chemistry student at Johns Hopkins
University working for Ira Remsen; he noticed that the bread he
was eating was unusually sweet, and went back to his lab bench
and tasted all of the compounds he had been working with that
day to find the compound responsible. It was marketed
commercially as a non-nutritive sweetener very quickly,
especially for use by diabetics. It was banned in some areas for
some time because it was a suspected carcinogen.
58
Chapter 7 Notes

Aspartame (NutraSweet)
O OCH3
O

O
N
Aspartame (NutraSweet)
H NH2 OH
Aspartame (NutraSweet) is about 160 times sweeter than sugar; it
is composed of the amino acids aspartic acid and phenylalanine,
neither of which has a sweet taste. It was discovered at Searle by
James Schlatter in 1965, who was preparing intermediates for the
synthesis of a tetrapedtide for an anti-ulcer project. Schlatter had
spilled some of the dipeptide intermediate on his hands, and
noticed later that there was a strong, sweet taste; he went back to
his bench and tasted the dipeptide and found that it indeed was
extremely sweet. Aspartame is sensitive to heat, so it cannot be
used in cooked foods, and it decomposes slowly in liquids,
reducing their shelf life. 59

H O

N
OSO2- N– K+

S O
Cyclamate CH3 O
Discovered by Michael Sveda in O
Acesulfame-K (Sunette)
1937, who noticed that a cigar that Approved by the FDA in 1988;
he was smoking in the lab tasted 200 times sweeter than sugar;
especially sweet. Cyclamates were noncaloric; heat-stable and can
banned by the FDA in 1970. be used during cooking

60
Chapter 7 Notes

CH2OH

H OH CH2OH
Cl ClCH2
O O
HO H OH HO
O
H OH CH2Cl
"galactose" OH
OH "fructose"
H OH
Sucralose
CH2OH A non-caloric artificial sweetener
Sorbitol approved by the FDA in 1998.
A sugar alcohol; incompletely The glucose in sucrose is replaced
absorbed during digestion, and by a galactose, and three of the OH
contribute fewer calories than groups are replaced by Cl atoms.
carbohydrates; found naturally in The molecule still tastes sweet, but
fruits; used commercially in is not metabolized in the body.
sugar-free candies, cookies,
chewing gum, etc.
61

The Maillard Reaction

• The Maillard Reaction occurs between foods
containing carbohydrates and proteins under heating;
it results in a complex mixture of products and the
development of a brown color. It is observed in the
grilling or browning of meats, the formation of crust
on baked breads, the boiling of maple syrup, the
brewing of beer, the roasting of coffee and cocoa
beans, the roasting of nuts, and other sources. In
addition to the darkened colors, many complex
flavors are developed. There are hundreds of
compounds produced during these reactions, not
many of which are well-characterized.

H
O
Furfural O

62