Ascorbic acid 396 Subject

Colorimetric procedures used In steroid assays are often subject to drug Interference. In the determination of 17-Ketosterolds by the Zimmerman reaction, drugs with the 17-Keto basic structure such as ascorbic acid, morphine and reserplne will cause Increased values. In the determination of 17,21 -dlhydroxysterolds by the Porter-Sllber reaction the dlhydroxy-acetone chain Is the reactive unit. Drugs like meprobamate, chloral hydrate, chloropromazlne and potassium Iodide will Interfere with this reaction and cause elevated values. In the colorimetric determination of vanlllylmandellc acid (VMA) by a dlazo reaction, drugs like methocarbamol and methyl dopa cause... 

Malo, J.L., Cartier, A., Pineau, L., Archeveque, J., Ghezzo, H. and Martin, R.R. (1986). Lack of acute effects of ascorbic acid on spirometry and airway responsiveness to histamine in subjects with asthma. J. Allergy Clin. Immunol. 78, 1153-1158. 

Camire (2002) showed that texturization does not seem to have a great effect on mineral retention and bioavailability. Others have reported increased retention of ascorbic acid in rice- and maize-based snacks (Hazell and Johnson, 1989 Plunkett and Ainsworth, 2007), increased iron diffusibility and absorption of iron-complexed protein (Poltronieri et al, 2000 Watzke, 1998), and no difference in iron and zinc absorption in human subjects fed textured bran-flour (Fairweather-Tait et al, 1989). 

Fig. 13 (Top) Influence of food on the absorption of different doses of riboflavin. (Bottom) Influence of food and divided doses on ascorbic acid absorption in three subjects. (Based on data from Refs. 39 and 77.)...

The selection of an appropriate antioxidant depends on factors such as stability, toxicity, efficiency, odor, taste, compatibility with other ingredients, and distribution phenomena between the two phases. Antioxidants that give protection primarily in the aqueous phase include sodium metabisulfite, ascorbic acid, thioglycerol, and cysteine hydrochloride. Oil-soluble antioxidants include lecithin, propyl gal-late, ascorbyl palmitate, and butylated hydroxytoluene. Vitamin E has also been used, but its virtue as a natural antioxidant has been the subject of some controversy. 

The main value of ACU measurement is that it makes it possible to give a fast estimate of vitamin C deficiency because in healthy subjects ascorbic acid is about 90% of total ACU [33], A strong deficit of ACU, possibly due to vitamin C deficiency, was found in patients with breast tumors (Fig. 11). 

There are a few areas in the subjects covered by this book where unfortunately the same words or are used to describe different things. They are gluten and flour improver. In food law a flour improver would cover a substance added to flour to improve its performance, usually in bread. Such a substance is ascorbic acid. In a bakery, the expression flour improver covers a mixture that is added to the dough. In this context a flour improver will contain not only substances like ascorbic acid but also, for example, enzyme active soya flour, emulsifiers and possibly fat. 

Autoxidation reactions of L-ascorbic acid (H2A) have been the subject of intensive studies for decades. It was shown that some of the most... 

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. 

Waters are the subject of a voluminous literature, and various methods have been proposed to overcome some of the interferences encountered, e g. by adding ascorbic acid or lanthanum to remove interferences when determining lead in hard water. Saline waters present particular problems (e.g. from background absorption), and a preliminary separation may be advisable. 

The direct Ripper iodometric titration is still used, but it is subject to error. In its place, direct iodate-iodide titration is used (44). This is followed by fixing the sulfur dioxide with glyoxal in a second sample and retitrating. The difference represents the free sulfur dioxide. The second titration roughly represents the amount of reduction and the amount of ascorbic acid present. Formulas for calculating the amount of sulfur dioxide to add in order to produce a predetermined level of free sulfur dioxide have been given by Stanescu (45). 

Antioxidants (e.g. BHA, ascorbic acid) Less than 100 ppm, subject to user-country legislation Prevent oxidation, limit flavour and colour deterioration... 

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). 

Previous studies have shown that rats maintained on a vitamin E-deficient diet had higher mortality rate than those of the -supplemented group when subjected to an acute dose of smoking exposure (42). Relatively greater increases in the levels of ascorbic acid, glutathione and related enzymes, glutathione-S-... 

Disaccharides and polysaccharides are also oxidized by the same degradative oxidation at first they react rapidly then, when the point of branching is reached, they react much more slowly. When subjected to similar oxidations, ascorbic acid affords threonic acid and oxalic acid, and 2-deoxy sugars yield 2-deoxyaldonic acids and lower alditols. 

In reconstructed human epidermis the presence of vitamin C was required to normalize stratum corneum lipids, which was accompanied by an improvement of skin barrier formation.36 Interestingly the ascorbic acid concentration in the skin of atopic dermatitis37 and psoriatic patients38 measured in vivo by microdialysis was significantly lower than in healthy subjects. In psoriasis there was no significant difference in lesional versus nonlesional skin. There has also been demonstrated a decrease of ascorbic acid concentration in skin with increasing age.39... 

An example of the selectivity of diamond electrodes is the detection of dopamine in the presence of 1000-fold excess of ascorbic acid (typical of the composition of neural extracellular fluid). On an H-terminated diamond, potentials of the dopamine (DA) and ascorbic acid (AA) oxidation peaks on potentiodynamic curves are very close each other the peaks cannot be resolved (Fig. 32). To impart selectivity to diamond electrode, it was subjected to anodic pre-treatment (discussed in Section 6.2). The treated electrode exhibited a substantial shift in the positive direction for the peak potential for AA oxidation, thus making it possible to discriminate between the DA... 

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