Transcript 14 Carbohydrates

FOOD CHEMICALS
Chemical Makeup: 99% CHON; Next 1% = Na/K; Mg/Ca; P/S/Cl
Humans: 47 elements present; 24 at are necessary
AN AVERAGE ADULT NEEDS
2400 kcal (2000-3000) PER DAY = 100 kcal/hour
NOTE: One food Cal = 1 kcal (= 4.8 kJ)
ONE POUND OF FAT = ~4000 kcal ~ 2 days food
1 KILO OF FAT = 9000 kcal
~ 4 days food
fat uses up the daily calorie intake rapidly and it takes a lot of
exercise to get rid of!
cycling 20 km/h for 1 h:
walking up hill ~300m height gain:
Resting metabolic rate (4am sleeping):
Non energetic stuff:
~ 600 kcal
~ 600 kcal
~ 50 kcal/h
~ 70-100 kcal/h
CARBOHYDRATES Cn(H2O)m hence name
Monosaccharides have ONE sugar: egs. glucose, fructose, ribose
Disaccharides have TWO sugars: egs. sucrose, maltose, lactose
Oligosaccharides have a FEW sugars: eg. raffinose
Polysaccharides have MANY sugars: egs. starch, cellulose
Carbohydrates store water as well as being an energy source
MONOSACCHARIDES
GLUCOSE
C6H12O6
Mirror
CH 2OH
HOCH 2
H
b-(+)-D-glucose
note b = up
O OH
OH H
HO
H
H OH
HO
H
O
H
H HO
OH
(-)-L-Glucose
(not found in nature)
OH H
water
CH 2OH
H
open form
(low conc)
OH
OH H
HO
CHO
H OH
CH 2OH
water
H
O H
OH H
HO
OH
H OH
a-(+)-D-glucose
note a = down
b and a glucose are two different chemicals
Glucose = blood sugar = dextrose: needs no digestion,
can be used IV
H
H
HOCH2
HO HO
O
H
H
OH
OH
H
in reality rings are not flat
have a chair like structure
bonds are equatorial
or axial
NOTE: in glucose all the H’s are axial, all the OH equatorial
CH2OH
H
O OH
H
OH H
H
HO
H OH
If we flatten the ring, then notice
the groups alternate – this is one
way to recognize glucose!
IF YOU SWITCH AN OH GROUP, YOU CHANGE THE SUGAR
(+)-D-Galactose
CH 2OH
has this OH changed
HO
O OH
OH H
H
H
H OH
note: this can still
be a or b
we show this with
a wiggly line:
CH 2OH
HO
O
OH H
H
H OH
OH
We will meet this sugar later
in lactose (milk)
SOME SUGARS HAVE THE SAME FORMULA BUT MAKE 5membered rings: eg. FRUCTOSE
HOCH 2
O
H
HO H HO
HO
C6H12O6
CH 2OH
H
(-) - D- Fructose (levulose), happens to
be a (-) sugar present in invert sugar,
fruit sugar
Sweetest sugar: ‘high fructose corn syrup’ need less to sweeten
BUT fructose stimulates liver to release fats in to blood stream just
like insulin, leads to insulin resistance promotes type II diabetes
HOCH 2
(-) - D- Ribose used in RNA
O
HO H H
HO
OH
OH (H)
(deoxyribose, used in DNA, has H
instead of OH)
DI-SACCHARIDES most important in foods
R-O-R'
R-OH + HO-R'
- water
HO
O
O
O
OH
+ HO
OH
HO
O
O
OH
acetal
two molecules of a mono-saccharide can ‘condense’ with loss of a
molecule of water to form a disaccharide:
2 (C6H12O6) - H2O = C12H22O11
MALTOSE uses two glucose molecules, (+) sugar
CH2OH
H
CH2OH
O H
a-Glu-4-Glu
O
4
OHH
H
OHH
OH
HO
O
1
2
H OH
3
H OH
all animals can easily cleave a links
(eg. we have the enzymes in our
saliva) back to (in this case) 2 glucoses
a link 4-link
Other saliva enzymes cleave starch to maltose:
try chewing some bread it gets sweeter as you chew
Note: this link is not interconvertible once formed, i.e. a stays a,
b stays b
SUCROSE: Table sugar (>80M tons/y)
CH2OH
H
O H HOCH2
O H
OHH
H HO
CH2 OH
HO
O
HO H
H OH
a-Glu-(2)-Fru
(+) sugar
a link
So we can split this to glucose and fructose – we can only directly
metabolize monosaccharides
The liver can inter-convert glucose and fructose as needed but as
before too much fructose is not good!
LACTOSE,
Milk sugar (+)
CH2OH
CH 2OH
Galactose
HO
O
H4
O
OH H
b-Gal-4-Glu
H
H
O
OHH
OH
1
2
3
H OH
H OH
b link
All babies have lactase which can cleave the b-link, when weaned
all animals and most humans (except those of European descent)
LOSE this enzyme and so do not tolerate lactose well
Lactose goes to colon, where bacteria convert it to gas + lactic
acid (CH3CHOHCOOH), which irritates bowel and causes
diarrhea; human milk ~ 7.5 g lactose/100 mL; cows ~ 4.5
Sweetness(relative): Fructose 1.7; Sucrose 1; Lactose 0.16
POLYSACCHARIDES
STARCH, Amylose = water soluble portion of starch (20-25%)
AMYLOSE
O
O
O
O
O
O
ALL a-links
O
-[a-Glu-4-Glu-]n-
O
n
n = 15-250
rest is AMYLOPECTIN
1000-5000 Glu units (3D) crosslinked using the CH2OH
Plants store STARCH for energy usage (plus a lot of water - they do not
have to move!)
Animals use GLYCOGEN: stored in liver and muscles in small amounts
(otherwise too much water): more branched and cross-linked than
amylose, but still all a-links for fast breakdown to glucose for usage
Starch cannot pass thru intestine, so to be absorbed, it is broken down
by maltase into MALTOSE
Amylose when heated & cooled sets to gel: PUDDINGS, CANDIES
Amylopectin goes more pasty: GRAVIES, SAUCES
Both form an intense blue colour with Iodine/iodide (I3-) - test
UTILIZING STARCH
a) All creatures can convert
glucose ↔ fructose → pyruvic acid CH3COCOOH
Then we use pyruvic acid in the Kreb’s cycle, WITH O2, to convert ADP
to ATP, CO2 + H2O + energy
If there is insufficient O2 (eg. in starved muscles), pyruvic acid
converts to CH3CHOHCOOH (lactic acid) + energy
Lactic acid causes pain in muscles (cramps): slowly reconverts to
pyruvic acid in the presence of O2
b) To make beer:
Barley contains enzymes that convert starch to maltose during the 12h cooking time of the ‘mash’
Yeast enzymes then convert maltose to ethanol, CO2 and heat
CELLULOSE
O
O
O
O
O
O
O
-[-b-Glu-4-Glu-]n-
O
n
all b-links
Most creatures do not have cellobiase which can cleave the b-links
Cows, goats, horses, termites, etc. have bacteria in their rumens
(2nd stomach) which have the enzymes to cleave cellulose so can
eat grass, etc.
Theoretically, could cleave the b-link in the lab with aqueous acid
to liberate glucose but it is too expensive to remove the sugar
from acid to be practical
Paper, rayon, cotton, cellophane: cellulose chains with H-bonds
Weaken in water (can shape) but stiffen when dry (stale bread)
Can stiffen cotton with starch; can use starch to paste paper
Most foods have too much sugar: eg. ketchup, 29%
Consumption: 50-60 kg sugar/year per person
Excess sugar consumption:
obesity, atherosclerosis, dyspepsia, diabetes
Diabetes:
Type 1 too LITTLE (or no) insulin
too much sugar in blood
Type 2 insulin resistance
Hypoglycemia: too low blood sugar
(tired, poor thinking ability)
GALACTOSEMIA (rare: 10-20 / million of population)
unable to convert galactose to glucose in liver;
Gal deposits in eye, get cataracts
BAKED BEANS
have 0.5-10% galactose as the trisaccharide
RAFFINOSE = Gal-b-4-Glu-Fru
no enzymes for this so it goes to the intestines where bacteria
convert it:
smelly gas! (mostly H2S/Me2S2/MeSH ) from S-containing amino
acids (proteins)
People who require colon surgery have a polyethyleneglycol purge
to clean pipes to prevent colonic detonations during surgery
(spark-methane)!!!
BEANO: contains the enzyme alpha galactosidase to allow people
to break down Raffinose; has been added to beer to break down
complex sugars – lower carb beer but less flavour and less head