Download Vitamins




s
Very small amounts are needed by the body (>1 gm)
Very small amounts are contained in foods.




The roles they play in the body are very important.
Most vitamins are obtained from the foods we eat.
Some are made by bacteria in the intestine




They do not contain kcalories.
Fat Soluble Vitamins vs.
Water Soluble Vitamins
Found in fats and oils
Require bile for absorption
Enter the lymph, then the blood
Held and stored in fatty tissues
Needed in small amounts
May reach toxic levels
Not readily excreted
• 3 forms in the body
– Retinol
– Retinal
– Retinoic acid
• collectively known as
• precursor: beta-carotene
– derived from plant foods
– can split and form retinol in intestine and liver
• Beta-carotene found in:
– Dark leafy green vegetables
– Deep orange veggies
– Deep orange fruits
 Vision
Maintain epithelial tissue and skin
Support reproduction and growth
Immune system
Bone development
• Deficiency
–Infectious disease
• Pneumonia, measles, diarrhea
–Keratinization
• Dry, rough, scaly skin
–Night blindness
 body can make vit D
−from sunlight
−precursor made from cholesterol
 production occurs in liver and
kidney
 diseases can affect activation
sources
fortified food, milk, margarine,
cereals, beef, eggs
sun
Part of the bone-making/maintenance team
Maintains blood concentrations of ca & P
Mineralization of bones
− Raises blood calcium and phosphorus by increasing
absorption from digestive tract
− Deposition of calcium and phosphorus into bones
− Stimulating retention by kidneys
Deficiencies
Infections
Osteomalacia or rickets
• Antioxidant
– Defender against free radicals
• Polyunsaturated fatty acids
• May reduce the risk of heart disease
• Widespread in food
– Easily destroyed by heat processing
• Deficiencies
– Rare
– Erythrocyte hemolysis
An antioxidant is a molecule that inhibits
the oxidation of other molecules.
• Aids in blood clotting and
Bone mineralization
• Deficiency causes
hemorrhagic disease
• Sources
– Made by bacteria in GI tract
– Absorbed and stored in liver
The B-complex vitamins are often associated with
giving a person more energy. This is due to the fact
that these vitamins each play different roles with
energy metabolism in the body. When they are
present in the body, they allow energy to be used more
readily by the body.
Since these vitamins are water soluble, they are not
stored in the body like fat soluble vitamins. They
dissolve in water and are excreted from the body in
urine. Therefore, it is important to consume foods rich
in these vitamins each day in order to fulfill the
body’s need.
• Co-enzymes (activate enzymes)
• Found in the same foods
– Single deficiency rare
• Act together in metabolism
– Metabolic pathways used by
protein, carbohydrate, and fat
Thiamin (B1)
Riboflavin (B2)
Niacin (B3)
Pantothenic Acid
Biotin
Pyridoxine (B6)
Folate
Vitamin B-12
• Energy metabolism
– Thiamin (B-1), Riboflavin
(B-2), Niacin (B-3),
Pyridoxine (B-6), Biotin,
Pantothenic Acid
• Red blood cell synthesis
– Folate, B12
• Homocysteine metabolism
– Folate, B12, B6
• Vitamin C (chemical name :
ascorbic acid).
• Synthesized by most
animals (not by humans)
• Decrease absorption with
high intakes
• Excess excreted
•
•
•
•
•
•
•
•
Citrus fruit
Potato
Green pepper
Cauliflower
Broccoli
Strawberry
Romaine lettuce
Spinach
 Reducing agent (antioxidant)
 Iron absorption (enhances)
 Synthesis of collagen
 Immune functions
 Does not prevent common colds
or flu, but may reduce duration
of symptoms day by a day
 Wound healing
 Easily lost through cooking
 Sensitive to heat
 Vitamin C (ascorbic acid) deficiency leads to scurvy,
a disease characterized by weakness, small
hemorrhages throughout the body that cause
gums and skin to bleed, and loosening of the teeth.
Sailors that were out at sea for months on end would often develop
scurvy unless the captain had the foresight to pack limes and other
citrus fruits.
 In the U.S., deficiency is seen mostly in alcoholic persons with poor
diets and older persons who eat poorly (no fresh fruits and
vegetables)
Scorbutic Rosary
Follicular
Hemorrhages
• Hemochromatosis (iron overload)
– Vitamin C enhances iron absorption
• Oxalate kidney stones
• Erodes tooth enamel
25
• Objective: To determine vitamin C (C6H8O6) by
potassium iodate titration
• Vitamin C is sometimes called an anti-oxidant. (i.e., a
reducing agent!) by pharmacists and food nutritionists.
• A suitable method for the determination of vitamin C
(C6H8O6) quantities is a titration with potassium iodate
(KIO3).
• Iodometric titrations. In "iodometric" titrations, the analyte
is first reduced with an excess of I-, producing I2 (actually,
I3-) which turns blue in the presence of starch.
• Potassium iodate is used as a titrant and it is
added to an ascorbic acid solution that contains
strong acid and potassium iodide (KI).
• Potassium iodate reacts with HCl in presence of
potassium iodide, liberating molecular iodine
(I2).
• Iodine rapidly oxidizes ascorbic acid, C6H8O6,
to produce dehydro-ascorbic acid
C6H6O6: C6H8O6 + I2
C6H6O6 + 2I. + 2H+
• The addition of acid is necessary to provide the
acidic conditions required in reaction above.
 Potassium iodide must be added in excess to keep
iodine dissolved.
 Once all the ascorbic acid has been consumed, any
excess iodine will remain in solution. Since aqueous
iodine solutions are brown in color, iodine can act as
its own indicator.
 However, it is quite difficult to detect endpoints using
iodine coloration alone, and it is more usual to add
starch, which forms an intensely blue colored complex
with iodine but not with the iodide ion.
 The endpoint of the titration is the first permanent
trace of a dark blue-black color due to the starchiodine complex.
1. KIO3 is used as a titrant and it is added to an ascorbic
acid solution that contains a strong acid and potassium
iodide (KI).
2. KIO3 reacts with HCl and KI, liberating molecular
iodine (I2):
KIO3 + 5KI + 6H+ → 3I2 + 6K+ + 3H2O …………(1)
C6H8O6 + I2 → C6H6O6 + 2I- + 2H+ …………..(2)
• According to the above reactions, each mole of
potassium iodate added corresponds to 3 moles of
ascorbic acid dehydrogenated in the sample.
Ascorbic acid
Ascorbic acid
Dehydroascorbic acid
Dehydroascorbic acid
The end point is reached when the solution
turns a permanent, dark blue color, due to the
complex formed between starch and iodine.
• During an iodometric titration an intermediate dark
blue iodine-starch complex may form momentarily,
before the iodine reacts with ascorbic acid.
• However, if the color disappears upon mixing, the
end point has not yet been reached.
• Thus, magnetic stirrers or glass rod are employed in
the titration to ensure proper mixing and to facilitate
the reaction of iodine with ascorbic acid.
• Molecular iodine (I2) is only slightly soluble in
water but adding iodide, I-(KI), produces the
"triiodide" ion (I3-) in solution. Thus, KI is
almost always added when redox reactions of I2
are involved in quantitative analysis.
I2(s) + I-(aq)
I3(aq)
Iodine iodide
triiodide
• Starch is used as the indicator in most iodometric
titrations because iodine (i.e., I3)forms an intense
blue colored "starch-iodine complex."
1. Pipette 25 ml of the provided ascorbic acid
solution into a 250 ml conical flask,
2. Add  4 ml of 2M HCl,
3. Add  5 ml of potassium iodide (KI) solution and 3 ml
starch solution.
4. Then titrate with the standard potassium iodate (KIO3)
solution until the solution turns intense blue. Write down the
standard potassium iodate (KIO3) solution volume.
5. Pipette 25 ml of an unknown ascorbic acid sample, a kind
of juice, into a 250 ml conical flask, then follow the same
procedure of steps 1-4 and write down the volume of the
standard KIO3 solution determine the concentration
(mol/ml) of ascorbic acid in the selected sample.
33
procedure