FREE Notes Food Chemistry - Knowledge clips Carbohydrates

Carbohydrates
Introduction to carbohydrates
 Ring structure of carbons and one carbon atom. OH groups connected.
Contain carbon, hydrogen and oxygen.
 Saccharose: two rings connected to each other.
 Oligosaccharides: 2-20 residues, for instance saccharose (disaccharides,
trisaccharide)
 Vitamin C: no carbohydrate because double bond in ring and double bonded
oxygen.
 Cyclodextrin: glucose units connected in a ring

Monosaccharides
 Aldose and ketose
o Ketone: double bonded oxygen is NOT on the first carbon but on the
second, third et cetera. In the case of sugars, you call this a ketose.
o Aldehyde: double bonded oxygen is on the first carbon. In the case of
sugars, this is an aldose
o Double bonded O becomes an OH group in the ring structure
o Anomeric carbon is the carbon that had the double bonded oxygen in
the open structure. This one is always between an oxygen atom and
the OH group that was the double bonded oxygen.
 Ketone has another C containing group attached to this anomeric
carbon.
 Aldehyde does not have another C containing group attached to
the anomeric carbon
 Pyranose or furanose
o Pyranose: 6 membered ring (O included)
o Furanose: 5 membered ring (O included)
 Hexose or pentose
o Hexose: 6 carbon atoms in the structure (side group included)
o Pentose: 5 carbon atoms in the structure (side group included)
 Alpha or beta anomer
o Double bonded oxygen becomes OH group when the ring closes. This
can point upwards or downwards.
o You have to look at the group that is at the anomeric carbon, so
between the O!!
o Alpha: downwards
o Beta: upwards relative to the structure
 Galactose: no C containing group at the anomeric carbon so aldose. Hexose
because 6 carbons in the structure
 Fructose: furanose (because 5 without side groups), hexose because 6
carbons
o Alpha: glucose is alpha because the original OH group is pointing
downwards
o Beta: fructose is beta because anomeric carbon (between O) should be
on the right side of the molecule. If you do this, you see that the group
is pointing upwards, so it is a beta anomer.

, Reducing properties
 Open form: double bonded oxygen
 Closed form: alpha-anomer = OH group downwards, beta-anomer = OH
group upwards
 Double bonded oxygen means reactive, open form. Maillard or caramelization
can take place. = reducing property
 You name it reducing because the carbonyl group (c with the double bonded o
 C=O) can reduce Cu2+. Form CU2+ to copper oxide CU2O
 Free OH group is reducing because when the ring opens up, you have a
double bonded oxygen that is reactive. If you have an O that is between two
monosaccharides, it cannot open up.
 Cyclodextrin is not reducing because the ring cannot open up, so no double
bonded, reactive O group.
 Important!! Look at the OH that is at the anomeric carbon. So between the O
and OH group.
 Mutarotation: fructose can close in different ways. You can get a furanose,
pyranose, beta form. When fructose is in solution, it can change into another
form by opening and closing.
 Lactose is reducing because free OH group that can become double bonded
oxygen that becomes reactive when opened
 Saccharose: you should look at the OH group on the left side but it is not
there. Both rings cannot open up.

Glycosidic bonds
 Bond that connects the monosaccharides in the carbohydrate
 For instance fructose and glucose are connected by a glycosidic bond. Water
molecule is formed when they connect. Glycosidic bond is the O in the middle.
 OH group of the monosaccharide downwards = alpha. Second
monosaccharide also have its OH group pointing downwards = alpha. If they
combine with each other





 If first is beta and second is alpha, you get the shape below. This is no
additional carbon atom! You name it beta when they are different.





 Systematic name of disaccharides.
o Galactose and glucose. Galactose has OH upwards = beta. First carbon
of galactose with fourth carbon of glucose. No alpha in front of glucose
because glucose is reducing  can both have alpha and beta form
(change)
 Saccharose: alpha 1-2. 2 because you start counting at the side of the
anomeric carbon  also count side groups!!