Vitamins Part 7 Deng Zeyuan

1.General Description and Common Characters of Vitamins Vitamins are organic compounds of low molecule weight. They are necessary for keeping natural physiological function, especially for intracellular specific metabolism. They can’t be synthesized in the body. They are not the material of the tissue. They exist in natural food in different form. They can’t supply energy.

Vitamins are needed in just minute amounts and often do not undergo any digestive process- they are simply absorbed “as is” in the intestine. Many vitamins function as coenzyme and are necessary adjuncts to enzymes in catalyzing specific metabolic processes in the body Vitamins are consumed in their functions and must be obtained regularly from dietary sources, since they are not produced in any appreciable amount in the body.

2. Classification Vitamin Solubility: determines classification  Water soluble (hydrophilic): B vitamins and vitamin C o found in watery compartments of food o moves directly into the blood after being absorbed o can travel freely in the blood o freely circulate in watery compartments of the body's cells o regulated and excreted when in excess by the liver easily – are less likely to have toxic effects when ingested in large amounts.

Fat soluble (hydrophobic)  Oil soluble Vitamins A, D, E, and K o found in fats and oils of food O need fat for their absorption o carried through the lymph to the blood o many times require proteins for transport in the blood o trapped in cells associated with fat o less readily excreted - tend to stay in fat storage sites – can build up to toxic levels with serious and potentially fatal results.

3. Bioavailability This refers to the degree that any vitamin is utilised by our bodies and depends upon: i. the concentration of the vitamin at the time of consumption. Water-soluble vitamins will often leach out of the food if it is boiled in water. ii. the actual form of the molecule present, since some forms are more easily converted than others into the active form. iii. the composition of the diet. This influence viscosity and pH and will have an effect on the absorption of the nutrient by our bodies.

Post harvest changes (including the slaughter of an animal) will often result in enzymes that change the vitamin content of the food. Oxidative enzymes will reduce the concentration of many vitamins and any labile ( 不稳定的 ) vitamins will be lost with storage. Bioavailability

4. Water soluble V —Function, Deficiency and toxicity, Requirement, Food Source 1) V B1 2) V B2 3) V B5 4) V B6 5) Biotin 6) Folic Acid 7) V B12 8) Choline 9) VC

5. Fat soluble V —Function, Deficiency and toxicity, Requirement, Food Source 1) VA and Carotinoid 2) VD 3) VE 4) VK