Carbohydrates

Question 1

what are the functions of carbohydrates

Answer 1

energy and carbon source
energy store
flavouring
functional ingredient (gum, probiotics)

Question 2

what are the 4 types of carbohydrate

Answer 2

monosaccharide
disaccharide
oligosacchardie
polysaccharides

Question 3

outline the characteristics of monosaccharides

Answer 3

• simple, one sugar unit
• C3H6O3
• aldoses and ketoses

Question 4

what are the characteristics of aldoses

Answer 4

has a carbon and a double bonded oxygen at the end of the chain
contains an aldehyde group

Question 5

what are the characteristics of ketoses

Answer 5

has a carbon and double bonded oxygen in the middle of the chain
contains a ketone group

Question 6

define chiral

Answer 6

cannot be placed on top of its mirror image

Question 7

examples of stereoisomers

Answer 7

D-…

L-…

Question 8

what are the two chiral forms

Answer 8

enantiomers

epimers

Question 9

what is an enantiomer

Answer 9

mirror reflection
compounds related by inverting the configuration at all asymmetric carbons
OH group pointing left = L-glucose
OH group pointing right= D-glucose

Question 10

what is an epimer

Answer 10

disastereomers with an inverted configuration at one asymmetric carbon

Question 11

what is a disastereomer

Answer 11

compounds related by inverting configuration at one or more chiral centres

Question 12

what is meant by the cyclic structure of monosaccharides

Answer 12

reaction occurs between -OH at C-5 and the aldehyde at C-1, producing a pyranose ring
this produces an new asymmetric centre at C1, with two new alpha and beta stereoisomers- called anomers
alpha anomer- above the ring
beta anomer- below the ring
the anomie’s are interchangeable by mutarotation

Question 13

give an example of a reducing sugar

Answer 13

all monosaccharides

glucose, fructose maltose, lactose

Question 14

give examples of naturally occurring food monosaccharides

Answer 14

glucose, fructose, lactose, ribose

Question 15

how is the anomeric carbon configuration determined

Answer 15

glucose

• CH2OH and OH are on opposite sides on the anomeric carbon
• 6 membered ring= pyranose

fructose

• CHOH and OH are on the same side of the anomeric carbon
• 5 membered ring= furanose

Question 16

example of a disaccharide

Answer 16

maltose

Question 17

how are disaccharides formed

Answer 17

the hemiacetal end is free to open or close
the hemiacetal group of the alpha-delta-glucose reacts with the OH group of the beta-delta-glucose and forms a glycosidic bond

two monosaccharides formed by the glycosidic bond

Question 18

how is sucrose formed

Answer 18

glucose and fructose = sucrose
head to head
no free anomeric carbon so is non-reducing
inversion on heating
made by plants

Question 19

sugar beet is…

Answer 19

UK grown and processed in 6 factories

seasonal (Sept- March)

Question 20

sugar cane is…

Answer 20

a tropical plant that is shipped raw to the UK
processed all year in 1 UK factory
has many uses (flavour, colour, sweetener)

Question 21

how is lactose made

Answer 21

glucose and galactose
head to tail
reducing sugar

Question 22

give an example of a non-reading sugar

Answer 22

sucrose, trehalose

Question 23

how is trehalose made

Answer 23

glucose and glucose
head to head
energy storage in insects
non-reducing sugar

Question 24

what are polyols

Answer 24

sugar alcohols

Question 25

how are polyols produced and what are they used for

Answer 25

produced by the hydrogenation if sugars and syrups
used to replace sugars
fewer calories
small effect of blood glucose and insulin levels
non-cariogenic (no tooth decay)
in chewing gum, toothpaste

Question 26

what are oligosaccharides

Answer 26

3-10 covalently linked monosaccharides
found in artichokes, garlic, onions
e.g galactooligiosaccharide

Question 27

what are polysaccharides

Answer 27

10+ monosaccharides
homopolysaccharides
- single type of monomer
- straight or branched chain
- e.g starch and cellulose

heteropolysaccharides

• two or more different monomers
• straight or branches chain
• e.g gellan gum