Download The Water-Soluble Vitamins

The Water-Soluble Vitamins
1. B-Vitamins:
•Thiamin
•Riboflavin
•Niacin
•Pantothenic Acid
•Biotin
•Vitamin B-6
•Folate
•Vitamin B-12
2. Vitamin C
3- Choline
Dr. Latifah Al-Oboudi 2012
Water-Soluble Vitamin Overview
• Like fat-soluble vitamins, water-soluble
vitamins are essential organic substances
needed in small amounts for the normal
function, growth, and maintenance of body
tissues.
Dr. Latifah Al-Oboudi 2012
Vitamins and related compounds (e.g., choline) work together to maintain
health.
Dr. Latifah Al-Oboudi 2012
Water-Soluble Vitamin Overview
• In contrast to the fat-soluble vitamins, only
small amounts of water-soluble vitamins are
stored in the body.
• The risk of water-soluble vitamins toxicity
tends to be low because they are readily
removed by kidneys and excreted in the urine.
• Tolerable Upper Intake levels have been set
for only 4 of the water-soluble vitamins and
choline.
Dr. Latifah Al-Oboudi 2012
Water-Soluble Vitamin Overview
• water-soluble vitamins are destroyed during
cooking easily.
• A food’s vitamin content can be decreased by
exposure to heat, light, air, and alkaline
substances.
• water-soluble vitamins can leach into cooking
water, whereas fat-soluble vitamins can leach
into cooking fats and oils.
Dr. Latifah Al-Oboudi 2012
Water-Soluble Vitamin Overview
• Retention of the B-vitamins and vitamin C is
greatest in foods that are prepared by
steaming, stir-frying, and microwaving. These
cooking methods limit exposure to heat and
water.
• Fruits and vegetables are especially important
sources of many vitamins.
Dr. Latifah Al-Oboudi 2012
Dr. Latifah Al-Oboudi 2012
Coenzymes: A common Role of B-Vitamins
• All B-vitamin form coenzymes, which are
small, organic molecules that are a type of cofactor.
• Metals (e.g., zinc or magnesium) are another
type of cofactor.
• Cofactors combine with inactive enzymes
(called apoenzymes) to form active enzymes
(called holoenzymes) that are able to catalyze
specific reactions.
Dr. Latifah Al-Oboudi 2012
The enzyme-coenzyme interaction. The B-vitamins form coenzymes,
which are compounds that enable specific enzymes to function.
Dr. Latifah Al-Oboudi 2012
Dr. Latifah Al-Oboudi 2012
Coenzymes: A common Role of B-Vitamins
• In foods, B-vitamins are present as vitamin or
as coenzymes, both of which are sometimes
bound to protein.
• Digestion frees B-vitamins from coenzymes or
protein.
• Unbound (free) vitamins are the main form
absorbed in the small intestine. Typically,
about 50 to 90% of the B-vitamins in the diet
are absorbed.
Dr. Latifah Al-Oboudi 2012
Coenzymes: A common Role of B-Vitamins
• Once inside cells, the coenzyme forms of the
vitamins are resynthesized.
• Vitamin supplements sold in the coenzyme
form have no specific benefits to consumers
because vitamins must be released from the
coenzyme before they can be absorbed.
Dr. Latifah Al-Oboudi 2012
Grains: One Important Source of B-Vitamins
• Grains are an important source of many Bvitamins. However, when grains are milled,
the seeds are crushed and the germ, bran, and
husk layers are removed. This refining process
leaves just the starch-containing endosperm,
which is the only portion of the grain used to
make white flour, as well as many bread and
cereal products.
Dr. Latifah Al-Oboudi 2012
When grains are milled, the bran and germ are removed and discarded,
leaving only the starch-rich endosperm.
Dr. Latifah Al-Oboudi 2012
Grains: One Important Source of B-Vitamins
• Because the discarded parts are rich in
nutrients, milling leads to a loss of vitamins
and minerals.
• To counteract this nutrient loss, bread and
cereal products made from milled grains are
enriched with 4 B-vitamins—thiamin,
riboflavin, niacin, and folic acid– and with the
mineral iron.
Dr. Latifah Al-Oboudi 2012
• This practice, however, still leaves the
products with less vitamin B-6, potassium,
magnesium, zinc, fiber, and phytochemicals
than in whole-grain products because whole
grains contain the germ and the bran, as well
as the endosperm.
Dr. Latifah Al-Oboudi 2012
• When compared with white
rice, brown rice has 93%
more vitamin B-6, 50% more
potassium, 160% more zinc,
435% more magnesium, and
550%more fiber.
• Similarly, compared with
white bread, whole-wheat
bread has 200% more
vitamin B-6, 250% more
potassium, 260% more zinc,
370% more magnesium, and
285% more fiber.
Dr. Latifah Al-Oboudi 2012
• Nutrition experts therefore recommend that
whole-grain products, such as brown rice,
oatmeal, and whole-wheat bread and pasta,
be consumed daily.
Dr. Latifah Al-Oboudi 2012
Table 13_03a
Dr. Latifah Al-Oboudi 2012
Dr. Latifah Al-Oboudi 2012
Absorption , Transport, Storage, and
Excretion of Thiamin
• Thiamin is absorbed mainly in the small
intestine by a sodium-dependent active
absorption process.
• It is transported mainly by red blood cells in its
coenzyme form(thiamin pyrophosphate).
• Little thiamin is stored; only a small reserve is
found in muscles and the liver.
• Any excess intake is rapidly filtered out by the
kidneys and excreted in the urine.
Dr. Latifah Al-Oboudi 2012
Absorption , Transport, Storage, and
Excretion of Riboflavin
• In the stomach, hydrochloric acid(HCL) release
riboflavin from its bound forms.
• Free riboflavin is absorbed primarily via active
transport or facilitated diffusion in the small intestine.
• In the blood, riboflavin is transported by protein
carriers.
• Riboflavin is converted to its coenzyme forms in most
tissues, but this occurs mainly in the small intestine,
liver, heart, and kidneys.
• A small amount of riboflavin is stored in the liver,
heart, and kidneys.
• Any excess intake is excreted in the urine.
Dr. Latifah Al-Oboudi 2012
Absorption , Transport, Storage, and
Excretion of Niacin
• Nicotinic acid and nicotinamide are readily
absorbed from the stomach and the small
intestine by active transport and passive
diffusion.
• After being absorbed, niacin is transported via
the portal vein to the liver, where it is stored or
delivered to the body’s cells.
• Niacin is converted to its coenzyme forms in all
tissues .
• Any excess niacin is excreted in the urine.
Dr. Latifah Al-Oboudi 2012
Absorption , Transport, Storage, and
Excretion of Pantothenic Acid
• The pantothenic acid portion of any coenzyme
A in the diet is released during digestion in the
small intestine. It is then absorbed and
transported throughout the body bound to
red blood cells.
• Storage is minimal and is in the coenzyme
form.
• Excretion of pantothenic acid is via the urine.
Dr. Latifah Al-Oboudi 2012
Absorption, Transport, Storage and
Excretion of Biotin
• In the small intestine the enzyme biotinidase
releases biotin from biocytin and other biotindependent enzymes found in foods, free
biotin is absorbed in the small intestine via a
sodium-dependent carrier, biotin is stored in
small amounts in the muscles liver and brain,
and its excretion is mostly via the urine,
although some excreted in bile.
Dr. Latifah Al-Oboudi 2012
Absorption, Transport, Storage, and
Excretion of Vitamin B-6
• The coenzyme form is normally converted to the free
vitamin form for absorption.
• Vitamin B-6 is transported via the portal vein to the
liver, where most of it is phosphorylated.
• From the liver, the phosphorylated forms(mainly plp)
are released for transport in the blood bound to the
transport protein albumin.
• Muscle tissue is the main storage site for vitamin B-6.
• Excess vitamin B-6 is generally excreted in the urine.
Dr. Latifah Al-Oboudi 2012
Absorption, Transport, Storage, and
Excretion of Folate
• To be absorbed, folate polyglutamates must be broken
down (hydrolyzed) in the GI tract to the monoglutamate
form.
• Consumed with food, as in fortified cereal grains,
absorption is slightly reduced.
• The portal vein delivers the monoglutamate form of folate
from the small intestine to the liver, where it is converted
to the polyglutamate form once inside a cell. ( This change
allows folate to be trapped in a cell.)
• then, folate is either stored in the liver or released into the
blood or bile.
• Folate is excreted in both the urine and feces
Dr. Latifah Al-Oboudi 2012
Absorption, Transport, Storage, and
Excretion of Vitamin B-12
• The absorption of vitamin B-12 is quite complex.
• In food, vitamin B-12 is bound to protein. HCL and
pepsin in gastric juice release vitamin B-12 from
these proteins.
• In the stomach, the free vitamin B-12 binds to Rprotein, which originates in the salivary glands.
• In the small intestine, pancreatic protease
enzymes release vitamin B-12
Dr. Latifah Al-Oboudi 2012
•then combines with intrinsic factor, a protein like
compound, produced by parietal cells in the
stomach, that enhances vitamin B-12 absorption.
• The vitamin B-12 intrinsic factor complex travels to
the ileum, where vitamin B-12 is absorbed and
transferred to the blood transport protein
transcobalamin.
• Although vitamin B-12 is continually secreted into
the bile, most of it is reabsorbed by enter hepatic
circulation, thereby efficiently “recycling” this
vitamin.
• Little vitamin B-12 is excreted in the urine.
• Normally, healthy adults absorb about 50% of the
vitamin B-12 in foods.
Dr. Latifah Al-Oboudi 2012
Dr. Latifah Al-Oboudi 2012