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Vitamins

         Vitamins are low-molecular-weight organic substances required in small amounts in the diets of higher animals for normal growth, maintenance of health, and reproduction. All animals need vitamins, but not every vitamin is required by all animals; e.g., vitamin C is needed only by humans, guinea pigs, monkeys, some birds, and some fish that lack the enzyme gulonolactone oxidase, which is required to make l-ascorbic acid from glucose via D-glucuronic acid. Plants and microorganisms can synthesize all vitamins.

          Vitamins are a group of heterogeneous substances that differ widely in their chemical nature and function. They are usually classified on the basis of their solubility in water and fats as water-soluble and fat-soluble vitamins. The latter group includes vitamins A, D, E, and K, found in foods associated with lipids. The water-soluble vitamins are ascorbic acid (vitamin C) and the vitamins of the B complex group-nitrogenous organic substances of varied chemical structures.         

vitamins

 

         Vitamins have a range of functions in different animals. They regulate metabolism, help to convert carbohydrates and fats into energy, and assist in the build of body structure, such as formation of bones and teeth. Most vitamins of the B complex group have coenzyme functions. Vitamins taken in excess of the body's needs are useless; excess water-soluble vitamins are excreted mainly in the urine. However, the excess fat-soluble vitamins are stored in the body and could become toxic in very large excess.

         Requirements for vitamins differ during growth and maturity, additional quantities being needed under special circumstances such as pregnancy and lactation. The actual daily requirements may also vary depending on inheritance, microbial flora of the intestine, and eating habits. Thus, the recommended daily allowances (RDAs) of vitamins may also differ from one country to other. The standards have been set by organizations such as FAO/WHO, MRC (Medical Research Council, UK), and NRC/NAS (Nutritional Research Council, National Academy of Sciences, USA).  

         Vitamins are distributed widely in natural foods; some foods are richer in certain vitamins and poor in others. Vitamin deficiency rarely occurs in persons eating a wide variety of natural foods. Green leafy vegetables, fruits, whole grain cereals, pulses, and nuts are fairly rich sources of different vitamins. Milk, eggs, and meat are good sources of the vitamin B complex group, but the organ meats, such as liver and kidney, are richer.

         Vitamins are lost in various ways. Food processing involving blanching, cooking, heating, irradiation, and removal of water ( drying), as well as trimming and peeling, can cause significant losses of vitamins and minerals. Most water-soluble vitamins may be lost during cooking through leaching. Vitamins lost during food processing may be added by fortification; the added vitamins may be either synthetic or natural. Vitamins may also be lost during storage of food.  

 

 

 

 

 

 

             

 

 

 

      

 

 

 

 

 

      

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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