Vitamin occurence

The first commercial synthesis of a vitamin occurred ia 1933 when the Reichsteia approach was employed to manufacture vitamin C (6). AH 13 vitamins ate available ia commercial quantities, and their biological functions have largely been estabUshed (7). A Hst of Nobel prize winners associated with vitamin research is given ia Table 2. 

Vitamins occur naturally in many foods and raw materials. However the natural contents are often supplemented in many food products to ensure an adequate intake, for example in infant formulae, breakfast cereals and clinical nutrition products. Vitamins are usually added as nutrients and thus not covered in this chapter but may also be added as food colours (riboflavin, carotenes). The reader should refer to the following references for recent developments in... 

Vitamins are required for satisfactory development or function of most yeasts. Wickerham (177) devised a complete yeast medium which included eight vitamins biotin, pantothenic acid, inositol, niacin, p-aminobenzoic acid, pyridoxine, thiamine, and riboflavin. The concentrations of these growth factors varied widely with inositol in the greatest concentration and biotin in trace amounts. Many of these vitamins are considered major growth factors for yeast multiplication and development, as noted in several studies and reviews (178, 179, 180, 181, 182). Generally, the benefit of adding vitamins to musts and wines has not been established as a normal winery practice. This lack of response is because vitamins occur naturally in sufficient quantities in grapes and are produced by yeasts themselves (3). 

Factors to consider in selecting a suitable extraction procedure are (a) the analytical information required, (b) the nature of the food matrix, (c) the form in which the vitamin occurs naturally or is added, (d) the nature and relative amounts of potentially interfering substances, (e) the stability of the vitamin in heat and extremes of pH, and (f) the selectivity and specificity of the analytical technique to be used. 

Because the vitamins occur in food in trace quantities, detection sensitivity is often an issue. Ultraviolet absorbance is the most common detection method. Fluorescence and electrochemical detection are used in specific cases where physicochemical properties permit and where increased sensitivity and selectivity are desired. Refractive index is seldom used, due to its lack of specificity and sensitivity. 

Vitamin A or a precursor must be provided in the diet. This vitamin occurs in various forms (vitamers) retinol (alcohol), retinal (aldehyde), retinoic acid and vitamin A palmitate (ester). Requirements for vitamin A are usually expressed in international units (IU) per kg of diet. The international standards for... 

Vitamins are minor components of foods that play an essential role in human nutrition. Many vitamins are unstable under certain conditions of processing and storage (Table 9-1), and their levels in processed foods, therefore, may be considerably reduced. Synthetic vitamins are used extensively to compensate for these losses and to restore vitamin levels in foods. The vitamins are usually divided into two main groups, the water-soluble and the fat-soluble vitamins. The occurrence of the vitamins in the various food groups is related to their water-or fat-solubility. The relative importance of certain types of foods in supplying some of the important vitamins is shown in Table 9-2. Some vitamins function as part of a coenzyme, without which the enzyme would be ineffective as a biocatalyst. Frequently, such coenzymes are phosphorylated forms of vitamins and play a role in the metabolism of fats, proteins, and carbohydrates. Some vitamins occur in foods as provitamins—compounds that are not vitamins but can be changed by the body into vitamins. Vitamers are members of the same vitamin family. 

This vitamin occurs in several forms the two most important are vitamin D2, or ergo-calciferol, and vitamin D3, or cholecalciferol. The structural formulas of these compounds are presented in Figure 9-4. Vitamin D does... 

This vitamin occurs in a series of different forms, and these can be divided into two groups. The first is vitamin K, (Figure 9-8), characterized by one double bond in the side chain. The vitamins K2 have a side chain consisting of a number of regular units of the type... 

This vitamin occurs in all living tissues, where it influences oxidation-reduction reactions. The major source of L-ascorbic acid in foods is vegetables and fmits (Table 9-13). 

Few natural sources are rich in vitamin B12. However, only very small amounts are required in the diet. Good sources are lean meat, liver, kidney, fish, shellfish, and milk (Table 9-23). In milk, the vitamin occurs as cobalamine bound to protein. 

The first commercial synthesis of a vitamin occurred in 1933 when the Reichstein approach was employed to manufacture vitamin C (6). All 13 vitamins... 

Vitamin rarely occurs in plants. However, Solanumglaucophjlhtm Solanum malaco hn Cestrum diumum and Trinetumflavescens have been shown to contain water-soluble glycosides of vitamin D analogues with 1 a,25-dihydroxy-vitamin D activity (16—22). The vitamin D content in various plant and animal materials is shown in Table 3. Vitamin occurs naturally in all animals (24). 

The average intake of pantothenic add, as free pantothenic add and as coenzyme A, acetyl-ooenzyme A, and long-chain fatty acyl-cocnzyme A, is S to 10 mg/day. An RDA for the vitamin has not been established because the vitamin is plentiful in a variety of foods. Pantothenic acid is present in all plant and animal foods. The richest sources of the vitamin are liver, yeast, egg yolk, and vegetables. In foods, the vitamin occurs mainly as coenzyme A,... 

Pantothenic add levels in foods and body fluids can easily be measured by microbiological assays. Lactic acid bacteria are used as the test organism. Where measurement of ihe vitamin occurring as coenzyme A is desired, the coenzyme must first be treated virlth hydrolytic enzymes to liberate the pantothenic acid prior to the microbiological assay... 

In the early 1940s. R. J. Williams et al. used the term folic add in referring to a vitamin occurring in leaves and foliage of spinach, from the Latin for leaf (folium). Prc i-ously. it was called vitamin M and vitomin Bt/. Since then, folic acid has been found in whey, mushrooms, liver, yciut. bone marrow, soybeans, and fish meal, oil of which are ex-ccllent dietary sources. The structure (.sec diagram) has been proved by synthesis in many laboratories (e.g.. see Waller et al. -"-... 

Thiamine absorption occurs primarily in the proximal small intestine by both a saturable (thiamine transporter) process at low concentration (Ipmol/L, or lower) and by simple passive diffusion beyond that, though percentage absorption diminishes with increased dose. The absorbed thiamine undergoes intracellular phosphorylation, mainly to the pyrophosphate, but at the serosal side 90% of the transferred thiamine is in the firee form. Thiamine uptake is enhanced by thiamine deficiency and reduced by thyroid hormone, diabetes, and ethanol ingestion. The gene for the specific thiamine transporter has been identified, and the transporter cloned. Thiamine is carried by the portal blood to the liver. The firee vitamin occurs in the plasma, but the coenzyme, TPP, is the primary cellular component. Approximately 30 mg is stored in the body with 80% as the pyrophosphate, 10% as triphosphate, and the rest as thiamine and its monophosphate. About half of the body stores are found in skeletal muscles, with much of the remainder in heart, liver, kidneys, and nervous tissues (including the brain, which contains most of the triphosphate). 

The B group vitamins and vitamin C serve as coenzymes or coenzyme precursors. The B complex includes thiamine, riboflavin, pyridoxine, niacin, pantothenic acid, biotin, folate, and cobalamin. Inositol, choline, and paraaminoben-zoic acid, usually classified as vitamin-like substances in humans, are sometimes included with the B-complex vitamins. They will be discussed briefly at the end of the chapter. The B vitamins occur in protein-rich foods... 

Pantothenic Acid. (R)-V-r2>4-Dihydroxy-3,3-di-methyl-l-oxobutyll-B -alanine D(+)-/V-(2,4-dihydroxy-3,3-dimethy1butyryl)-d-alanine chick antidermatitis factor. C--HjjNO, mol wt 219.23, C 49.30%, H 7.82%, N 6.39%, O 36.49%, A member of the B complex vitamins. Occurs everywhere in animal and plant tissue. The richest common source is liver, but jelly of the queen bee contains 6 times as much as liver. Rice bran and molasses are other good sources. Isoln from liver R. J. Williams ei at, J. Am. 

Only a very small amount of vitamin D is necessary for health —approximately 0.01 mg (400 international units, lU) per day. The vitamin is a fat-soluble vitamin, occurring in cod-liver oil, egg yolks, milk, and in very small amounts in other foods. Cereals, yeast, and milk acquire an added vitamin D potency when irradiated with ultraviolet light. The radiation converts the sterol ergosterol into calciferol (vitamin D,), which has vitamin-D activity. Calciferol differs from D3 in having the side chain —CH(CH3)CH=CHCH(CH3)CH(CH3)2 in place of —CH(CH3)CH2CH2CH2CH(CH3)2. 

Vitamin E was first recognized in 1922 as a dietary factor essential for normal reproduction in rats, hence its name tocopherol from the Greek tocos, birth, and pherein, to bring about. Vitamin E is a group of compounds of similar structure, the most active of which is a-tocopherol. This vitamin occurs in fish oil, in other oils such as cottonseed and peanut oil, and in leafy green vegetables. The richest source of vitamin E is wheat germ oil. 

Free riboflavin appears to be present to a significant extent in the retina of certain animals and fishes, in milk, and in the urine. The findings of Bessey, Lowry, and Love indicate that riboflavin, like the other B vitamins, occurs mostly in bound forms, FAD being the major constituent. The FAD content varies from 90% of the total riboflavin content of the muscle to 70% in the kidney. The remainder occurs mainly as FMN, with free riboflavin being present in only trace amounts. 

Vitamin Be occurs in a wide variety of biological tissues. The vitamin occurs predominantly in the bound form as the phosphate of pyridoxal or pyridoxamine. In almost all tissues the pyridoxal phosphate is the major form with the exception of liver, where pyridoxamine phosphate appears to be in great excess over the aldehyde form. ... 

The intake of the vitamin occurs usually in the forms of pyridoxal or pyridoxamine. 

The vitamin occurs in food as nicotinic acid, either as its amide or as a coenzyme. Animal organs, such as liver, and lean meat, cereals, yeast and mushrooms are abundant sources of niacin. Table 6.7 provides data on its occurrence in food. 

P-Carotene (provitamin A) occurs in large amounts in apricots, cherries, cantaloups and peaches. B-vitamins present in some fruits (apricots, citrus fruits, figs, black currants and gooseberries) are pantothenic acid and biotin. Other B-group vitamins occur at levels of no nutritional significance. Vitamins B12 and D and tocopherols are found in no more than trace amounts. 

Fat-soluble vitamins occur in the lipid fraction of foods [1], composed mainly of triglycerides and partly of sterols, phospholipids, and other lipoidal constituents. These substances, having solubility analogous to those of the fat-soluble vitamins, complicate the isolation of fat-soluble vitamins and constitute a source of interference during the following analysis [1,3]. 

Relatively large amounts of the vitamin occur in meat, and particularly in offal, eggs and some types of cheese. There is a low vitamin content in milk. 

Properties.—Vitamin D, or calciferol, CjgHjj.OH, is isomeric with ergosterol, but differs in optical activity, ultra-violet spectrum, and other properties. The vitamin occurs in colourless needles, m.p. 114-5-117° C., [a] ° = + 102-5°, in alcohol. The solutions show an intense absorption band in the region 265 m/x. The vitamin gives none of the carotinoid reactions characteristic of vitamin A. 

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