The Water-Soluble Vitamins

1. 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-Oboudi2012

2. Water-Soluble Vitamin Overview • Like fat-soluble vitamins,water-soluble vitaminsare essential organic substances needed in small amounts for the normal function, growth, and maintenance of body tissues. Dr. Latifah Al-Oboudi2012

3. Vitamins and related compounds (e.g., choline) work together tomaintain health. Dr. Latifah Al-Oboudi2012

4. 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-Oboudi2012

5. 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-Oboudi2012

6. 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-Oboudi2012

7. Dr. Latifah Al-Oboudi2012

8. Coenzymes: A common Role of B-Vitamins • All B-vitamin form coenzymes, which are small, organic molecules that are a type of co-factor. • Metals (e.g., zinc or magnesium) are another type of cofactor. • Cofactorscombine with inactive enzymes (called apoenzymes) to form active enzymes (called holoenzymes) that are able to catalyze specific reactions. Dr. Latifah Al-Oboudi2012

9. The enzyme-coenzyme interaction. The B-vitamins form coenzymes, which are compounds that enable specific enzymes to function. Dr. Latifah Al-Oboudi2012

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11. 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-Oboudi2012

12. 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-Oboudi2012

13. Grains: One Important Source of B-Vitamins • Grains are an important source of many B-vitamins. 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-Oboudi2012

14. When grains are milled, the bran and germ are removed and discarded, leaving only the starch-rich endosperm. Dr. Latifah Al-Oboudi2012

15. 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-Oboudi2012

16. 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-Oboudi2012

17. 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-Oboudi2012

18. 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-Oboudi2012

19. Table 13_03a Dr. Latifah Al-Oboudi2012

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21. 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-Oboudi2012

22. 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-Oboudi2012

23. 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-Oboudi2012

24. 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-Oboudi2012

25. Absorption, Transport, Storage and Excretion of Biotin • In the small intestine the enzyme biotinidase releases biotin from biocytin and other biotin-dependent 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-Oboudi2012

26. 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-Oboudi2012

27. Absorption, Transport, Storage, and Excretion of Folate • To be absorbed, folatepolyglutamates 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

28. 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 R-protein, which originates in the salivary glands. • In the small intestine, pancreatic protease enzymes release vitamin B-12 Dr. Latifah Al-Oboudi 2012

29. 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

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