Carbohydrates

Question 1

monosaccharides

Answer 1

glucose, fructose and galactose

Question 2

disaccharides

Answer 2

maltose (glu-glu), lactose (glu-gal), sucrose (glu-fru)

Question 3

Solubility of polysaccharides

Answer 3

• hydrogen bonding between OH residues and water
• surface have strong affinity for water
• at high temp, most take up water, swell and undergo dissolution

Question 4

Starch

Answer 4

• discrete particules/granules
• dense and insoluble
• disperse in cold water to give low viscosity slurries
• thickening properties on heating
• 2 polymers: amylose and amylopectin

Question 5

Amylose

Answer 5

• 25% of starch
• linear
• 20-50KDa molecular weight
• a-D(1-4) links
• a-D(1-6) links (0.3-0.5%)
• right handed helical shape
• interior highly hydrophobic

Question 6

Amylopectin

Answer 6

-75% starch
-highly branched
-molecular weight >1000kDa
-a-D(1-4) links (95%)
-a-D(1-6) links (5%)
neighbouring branches coil together to form double helixes
double helixes bulky can’t fit in active site of animal amylase, so little nutritional value

Question 7

Starch granule

Answer 7

different crystal structures in alternating layers
crystallisation - highly organised structure
branches of amylopectin occur as packed double helices
branches of amylopectin 20 gluc long
amylose contains 100-300 flu units
amylose molecules may connect/cross-link different amylopectin molecules by integrating into double helices
show birefringence patterns when viewed in polarised light

Question 8

Starch gelatinisation

Answer 8

undamaged starch granules are insoluble in cold water
when heated undergoes gelatinisation
this disrupts the molecular order in the granule
-irreversible swelling
-loss of birefringent
-loss of crystallinity
-amylopectin goes from being tightly coiled to loose bundle allowing water to move freely in and out

Question 9

retrogradation

Answer 9

cooling of hot starch sol forms rigid uniform gel
molecules rearrange themselves again to a more crystalline structure
properties change
-less soluble
-syneresis

Question 10

Modified starches

Answer 10

1. Starch acetates - low gelatinisation temp
   - hot drinks and sauce, improve texture, no lumps
2. hydroxy ethyl starches
   - less susceptible to retrogration
   - pie fillings, withstand baking
3. carboxymethyl cellulose
   - binder/thickener in puddings, cheese speeds