Ascorbic acid Vitamin changes

The word add comes from the Latin addus, meaning sour or tart, because in water solutions, acids have a sour or tart taste. Lemons, grapefruit, and limes taste sour because they contain citric acid and ascorbic acid (vitamin C). Vinegar is sour because it contains acetic acid. Another common property of acids is their ability to change the color of compounds known as acid-base indicators (Figure 9.1). 

The pattern of excretion of ascorbic acid is changed very little for the control subjects by the ingestion of 1 to 2 g of this vitamin per day for one week, but that for the schizophrenic subjects is shifted so that it becomes the same as for the controls. It is likely that the low excretors have a low body store of the vitamin, and that this store is brought up to the normal value by a sufiSciently increased daily intake. 

The resulting 2-keto-L-gulonic acid on enolization and lactonization yields L-ascorbic acid. This change has been shown by Eeichstein and Grllssner (1934) to occur readily if the free keto acid is heated in acid solution, whereas the formation of the vitamin from the methyl ester occurs spontaneously in buffer solutions over a pH range of 5 to 7 (Van Eekelen and Van der Laan, 1943). 

Use of an Oral Contraceptive. An estimated 10 to 11 million American women use oral contraceptives. Some have used them for many years prior to discontinuing their use in order to have a child. Researchers have found that these agents change the nutritional needs of some women. The levels of several vitamins and minerals in the blood are known to be, or suspected to be, influenced by the pill. As a result, some oral contraceptive users need increased amounts of certain nutrients in their diets to maintain normal blood levels (a sign of adequate nutrition). Folacin, a B vitamin, is of particular concern since many oral contraceptive users may need a supplement of folacin. In addition, adequate amounts of vitamin C (ascorbic acid), vitamin B-2 (riboflavin), vitamin B-6 (pyridoxine), vitamin B-12, and zinc are needed. 

FIA methods based on ferric reducing power similar to the FRAP principle reaction have been used for the determination of ascorbic acid, vitamin E, and total iron. Table 30.1 summarizes most of these studies. Spectrophotometric detection is also used in many of these studies because of the chromogenic effect from Fe oxidation, which changes with complex ligands, such as TPTZ, o-phenanthroline, cyanide, and DPPH. Different FIA manifolds have also been investigated and proposed, from single to multiple lines. Therefore, like other chromogenic antioxidant tests, the FRAP assay has the potential for several flow injection adaptations. 

Food process optimi2ation measurements may link a single chemical such as a vitamin, or a physical change such as viscosity, to process conditions and to consumer acceptance. Retention levels of ascorbic acid [50-81-7] C HgO, or thiamine can often be used as an indicator of process conditions (see... 

Mobilization and Metabolism. The total ascorbic acid body pool in healthy adults has been estimated to be approximately 1.5 g, which increases to 2.3—2.8 g with intakes of 200 mg/d (151—158). Depletion of the body pool to 600 mg initiates physiological changes, and signs of clinical scurvy are reported when the body pool falls below 300 mg (149). Approximately 3—4% of the body pool turns over daily, representing 40—60 mg/d of metabolized, or consumed, vitamin C. Smokers have a higher metaboHc turnover rate of vitamin C (approximately 100 mg/d) and a lower body pool than nonsmokers, unless compensated through increased daily intakes of vitamin C (159). The metaboHsm of ascorbic acid varies among different species. 

The isolation of ascorbic acid was first reported by Albert Szent-Gyorgyi (who called it hexuronie add) in 1928. The structure was determined by ITirst and Haworth in 1933, and, simultaneously, Reichstein reported its synthesis. Haworth and Szent-Gyorgyi, who together suggested that the name be changed to L-ascorbic acid to describe its antiscorbutic (antiscnrvy) activity, were awarded the Nobel Prize in 1937 for their studies of vitamin C. 

Deficiency may occur in infants if no fruits or vegetables are added to their milk formulas. In alcoholics, and in elderly subjects who consume inadequate diets vitamin C deficiencies are frequent. Severe ascorbic acid deficiency is characterized by the syndrome known as scurvy. Its manifestations are generally based on a loss of collagen. Symptoms include hemorrhages, loosening of teeth. In children cellular changes in the long bones occur. 

Several components with antioxidant activity are found in fruit juices. These include ascorbic acid, tocopherols (vitamin E), beta-carotene and flavonoids. Beta-carotene has antioxidant activity that can quench the singlet oxygen that can induce precancerous cellular changes. 

It must be noted at this point that, when Szent-Gyorgyi initially isolated 1, he unfortunately called it hexuronic acid. In early 1933, he and Haworth39 proposed that the name be changed to ascorbic acid. In 1965, the trivial name L-ascorbic acid was recognized by the IUPAC-IUB Commission on Biochemical Nomenclature40 as an acceptable name for vitamin C. The systematic name for L-ascorbic acid is L-threo-hex-2-enono-l,4-lactone. In the past, scorbutamin, redoxon, vitamin C, cevitamic acid, and hexuronic acid have been used as names for 1. Throughout this article, the trivial name L-ascorbic acid will be used for 1. 

The ease of oxidation of reduced ascorbic acid is the basis for a simple method of analysis by dye titration (58j. Ascorbic acid as it occurs in citrus juice is in the reduced form. When subjected to oxidation, ascorbic acid changes to the dehydro form. Dehydroascorbic acid has nearly the same physiological activity as the reduced form and is easily converted to the latter. Further oxidation of the dehydroascorbic acid converts it to 2,3-diketo-gulonic acid. This reaction is irreversible, and the oxidized product is devoid of biological activity. These reactions are shown in Figure 2. Nearly 90 percent or more of the vitamin C found in citrus juice and citrus products is in the reduced form (Table X) (59). 

Supplementation with the antioxidant vitamins ascorbic acid (250 mg) and mixed natural tocopherols (50 IU on alternate days) may be beneficial. Higher doses may vitiate the impact of lipid lowering therapy. Other naturally occurring antioxidants such as resveratrol, 3-catechin, selenium, and various carotenoids found in a variety of fruits and vegetables may provide additional antioxidant defense. Homocysteine, which initiates proatherogenic changes in endothelium, can be reduced in many patients by restriction of total protein intake to the amount required for amino acid replacement. Daily supplementation with up to 2 mg of folic acid plus other B vitamins is also recommended. 

The structure of ascorbic acid resembles an alpha-hydroxy acid, which is generally not appreciated. Ascorbic acid is present in most fruits, and may underlie some of the effects attributed to fruit extracts. Vitamin C has pronounced HA-stimulating effects in the fibroblast assay. But its antioxidant activity confounds the effects it may induce. The deposition of HA is stimulated when Vitamin C is added to cultured fibroblasts. The most profound changes occur in the compartmentalization of HA. The preponderance of the enhanced HA becomes cell-layer instead of being secreted into the medium.240,261 The chemical reactions catalyzed by ascorbic acid that bind HA to cell or matrix components are not known. 

To obtain silica nanocomposites with immobilized antioxidants, and to test their antioxidant activity, vitamins C and E were adsorbed onto nanosilica from ethanol solution containing both vitamins. A desorption experiment was then carried out. After the desorption of ascorbic acid from modified silica (0tms -0.40) into aqueous medium, the solvent was changed and the desorption of vitamin E into ethanol was studied. As one can see (Figure 6), both vitamins can be released from the surface for 1-2 hours. It should be noted that no increase in vitamin C concentration was detected in aqueous solution after its contact with A-200 for more than 30 min. Thus, as is the case for vitamins Bj and B6, desorption of vitamin C from the surface of modified silica is slower in... 

Ascorbic acid is a vitamin in primates. In most other animals, it can be synthesized by a branch of the glucoronic acid pathway (Chapter 18). It is apparently not changed into any coenzyme in the human being and participates as a vitamin in a reducing capacity in several biochemical reactions. These include the post-translational hydroxylation of proline in collagen biosynthesis (Chapter 8) and in tyrosine metabolism (Chapter 20). Ascorbic acid is oxidized to dehydroascorbic acid, a diketo derivative of ascorbate. Scurvy is a deficiency disease caused by a shortage of dietary ascorbic acid. In children, this results in defective bone formation in adults, extensive bleeding occurs in a number of locations. Scurvy is to be suspected if serum ascorbic acid levels fall below 1 jug/mL. 

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