Stability ascorbic acid

Stability. Ascorbic acid, a white crystalline compound, is very soluble ia water and has a sharp, acidic taste. In solution, the vitamin oxidizes on exposure to air, light, and elevated temperatures. Solutions of ascorbic acid turn yellowish, followed by development of a tan color. Ascorbic acid is stable to air when dry but gradually darkens on exposure to light. 

Ascorbic acid (0.8% w/v) in aqueous solution degraded according to apparent first order kinetics, with a rate constant of 2.34 x 10 2/hour, when irradiated by artificial sunlight [40]. The presence of 5% aspartame in the solution decreased the rate constant to 1.48 x 10 2/hour, thus stabilizing ascorbic acid to photochemical degradation by about 37%. Similar effects were also seen with some carbohydrate sweeteners. 

It has been found that glucose, sucrose, casein, albumin, sodium chloride, flour groats, and starch stabilize ascorbic acid (vitamin C).771 The addition of 5% of starch inhibits the decomposition of ascorbic acid.772 Studies on the stability of ascorbic acid, sodium ascorbate, erythorbic acid, and sodium erythorbate showed that some stabilization is observed after the addition of 8% starch.773 It was reported that the interaction is purely physical in nature.774... 

Edetic acid and edetates are primarily used as antioxidant synergists, sequestering trace amounts of metal ions, particularly copper, iron, and manganese, that might otherwise catalyze autoxidation reactions. Edetic acid and edetates may be used alone or in combination with true antioxidants the usual concentration employed being in the range 0.005-0.1% w/v. Edetates have been used to stabilize ascorbic acid ... 

Prompt stabilization of ascorbic acid is especially important in the case of plasma or serum samples. Metaphosphoric acid is often used for this purpose because it also serves as a protein precipitant. Such properties are desirable in the inactivation of oxidase and the catalytic eflFect of copper. Oxalic acid is an attractive stabilizer for ascorbic acid analysis because of its lower cost and greater stability however, it is not a protein precipitant, therefore, it has a limited use for the extraction of animal tissues. The use of ethylenediaminetetraacetic acid (EDTA) in addition to the metaphosphoric acid has been recommended (96). EDTA would chelate divalent cations, and a study has shown it will stabilize ascorbic acid in the presence of copper for several days (96). Perchloric acid has been used also but because of its inherent dangerous properties its use is generally avoided. Trichloroacetic acid and EDTA also seem appropriate extractants for ascorbate in plant materials (97). 

The change in colour of a 20% solution of povidone K 17 (Kollidon 17 PF) in water was from a slight yellow tint (Yellow 7 according to Ph.Eur.) to stronger yellow (Yellow 4) after thermal sterilization at 120-121 °C for 20 min. The addition of 0.2% of sodium bisulfite provided excellent colour stabilization. Ascorbic acid cannot be used as an antioxidant as it undergoes hydrolysis itself, giving rise to an even darker yellow-brown colour. 

USE Mainly in the protection of foods for the removal of glucose from egg albumin and whole eggs prior to drying. To remove oxygen from canned foods, soft drinks, beer, and stored food. In the manuf ol test papers for diabetes control and fertility tests. To stabilize ascorbic acid and vitamin B,-prepns. In combination with catalase, for treatment of food wrappers to prevent oxidative deterioration of food Sarett, Scott, U.S. pat. 2,765,233 (1956 to Ban L. Sarett). 

Dithiooxamide Dithioxamide EINECS 201-203-9 Ethanedithioamide HSDB 5230 Hydrorubeanic acid NSC 1893 Oxaldiimidic acid, dithio- Oxalic acid, dithiono-, diamide Oxamkfe, dithio- Rubean Rubeane Rubeanic acid RVK USAF B-43 USAF EK-4394 USAF MK-6. The amide of dithiooxalic aoid, a chelating agent, especially for copper, cobalt and nickel. Also used to stabilize ascorbic acid solutions. Red crystals mp = 170 (dec) X.m = 312 nm (s = 10300 MeOH) slightly soluble in H2O, EtOH, insoluble in organic solvents. 

Uric acid is a water-soluble antioxidant found in relatively high concentrations in plasma. It inhibits lipid peroxidation by tightly binding iron and copper ions into inactive forms, and by scavenging various oxidants such as hydroxyl radicals, peroxyl radicals, singlet oxygen and hypochlorous acid. By complexing with iron, uric acid stabilizes ascorbic acid in human serum. 

An ascorbic acid standard solution of 5 mg/mL has a pH value of 3. Thus, the stock standard can be made in distilled water. For dilute standard solutions, it is advisable to make the standard in acid, such as 5% metaphosphoric acid (MPA). For extracting biological samples, acids are used to precipitate proteins, to stabilize ascorbic acid and DHA and to remove interfering substances. MPA (62-64), trichloroacetic acid (TCA) (27,67), or perchloric acid (PCA) (53,68,69)... 

Liau et al. (76) compared amperometric and UV detection for ascorbic acid analysis. Their chromatographic system consisted of a C18 column and ammonium dihydrogenphosphate buffer with 0.015% MPA. For electrochemical detection they adjusted the pH of the mobile phase to 2.55 and for UV detection to 2.95. The amperometric detector was set at 700 mV versus Ag/AgCl reference electrode. The UV detector was set at 245 nm. They preferred relatively simple mobile phase without ion-pairing reagents which tended to precipitate with MPA that was present in mobile phase as well as in plasma sample for stabilization. Ascorbic acid was weU measurable with both detectors. The detection limit for electrochemical detection was 0.3 ng and for UV detection 1.2 ng per injection. The coefficient of variation (CV) for the between-day assay was <12% using electrochemical detection and <5% using UV detection. They conclude that UV detection is apparently a better choice for fast, routine measurements of ascorbic acid concentrations. Electrochemical detection takes more time to stabilize, but is more sensitive. 

Koh et al. used tricine buffer, pH 8.8, uncoated capillary 37 cm X 75 pm, and 11 kV voltage for separating ascorbic acid and lAA (internal standard) from urine, plasma, and serum (60). The capillary was treated with NaOH before use. They used either MPA or TCA for stabilizing ascorbic acid in the sample before the CE run. However, as found later, TCA may result in the loss of nearly 40% of the ascorbic acid content (63). The between-day coefficient of variation was 1.9% to 3.3%. The detection limit was 1.6 pg/mL and the method was linear to 480 pg/mL (60). 

CJ B ates. Use of homocysteine to stabilize ascorbic acid, or to reduce dehydroascor-bic acid, during HPLC separation of large volumes of tissue extracts. Clin Chim Acta 205 249-252, 1992. 

They have a synergistic effect on ascorbic acid, and they appear to stabilize ascorbic acid in human tissues. 

Physical Properties. Table 3 contains a summary of the physical properties of L-ascorbic acid. Properties relating to the stmcture of vitamin C have been reviewed and summarized (32). Stabilization of the molecule is a consequence of delocalization of the TT-electrons over the conjugated enediol system. The highly acidic nature of the H-atom on C-3 has been confirmed by neutron diffraction studies (23). 

In acidic solution, the degradation results in the formation of furfural, furfuryl alcohol, 2-furoic acid, 3-hydroxyfurfural, furoin, 2-methyl-3,8-dihydroxychroman, ethylglyoxal, and several condensation products (36). Many metals, especially copper, cataly2e the oxidation of L-ascorbic acid. Oxalic acid and copper form a chelate complex which prevents the ascorbic acid-copper-complex formation and therefore oxalic acid inhibits effectively the oxidation of L-ascorbic acid. L-Ascorbic acid can also be stabilized with metaphosphoric acid, amino acids, 8-hydroxyquinoline, glycols, sugars, and trichloracetic acid (38). Another catalytic reaction which accounts for loss of L-ascorbic acid occurs with enzymes, eg, L-ascorbic acid oxidase, a copper protein-containing enzyme. 

Many reactions catalyzed by the addition of simple metal ions involve chelation of the metal. The familiar autocatalysis of the oxidation of oxalate by permanganate results from the chelation of the oxalate and Mn (III) from the permanganate. Oxidation of ascorbic acid [50-81-7] C HgO, is catalyzed by copper (12). The stabilization of preparations containing ascorbic acid by the addition of a chelant appears to be negative catalysis of the oxidation but results from the sequestration of the copper. Many such inhibitions are the result of sequestration. Catalysis by chelation of metal ions with a reactant is usually accomphshed by polarization of the molecule, faciUtation of electron transfer by the metal, or orientation of reactants. 

The calcium form of EDTA instead of free EDTA is used in many food preparations to stabilize against such deleterious effects as rancidity, loss of ascorbic acid, loss of flavor, development of cloudiness, and discoloration. The causative metal ions are sequestered by displacing calcium from the chelate, and possible problems, such as depletion of body calcium from ingestion of any excess of the free chelant, had it been used, are avoided. 

Organic acids convert the blue mesomerically stabilized phenolate anion to the red undissociated acid. Reductones (e.g. ascorbic acid) reduce the reagent to a colorless salt. 

N-Nitrosamine inhibitors Ascorbic acid and its derivatives, andDC-tocopherol have been widely studied as inhibitors of the N-nitrosation reactions in bacon (33,48-51). The effect of sodium ascorbate on NPYR formation is variable, complete inhibition is not achieved, and although results indicate lower levels of NPYR in ascorbate-containing bacon, there are examples of increases (52). Recently, it has been concluded (29) that the essential but probably not the only requirement for a potential anti-N-nitrosamine agent in bacon are its (a) ability to trap NO radicals, (b) lipophilicity, (c) non-steam volatility and (d) heat stability up to 174 C (maximum frying temperature). These appear important requirements since the precursors of NPYR have been associated with bacon adipose tissue (15). Consequently, ascorbyl paImitate has been found to be more effective than sodium ascorbate in reducing N-nitrosamine formation (33), while long chain acetals of ascorbic acid, when used at the 500 and lOOO mg/kg levels have been reported to be capable of reducing the formation of N-nitrosamines in the cooked-out fat by 92 and 97%, respectively (49). 

Garcia-Viguera, C. and Bridle, R, Influence of structure on colour stability of anthocyanins and flavylium salts with ascorbic acid, Food Chem., 64, 21, 1999. 

De Rosso, V.V. and Mercadante, A.Z., The high ascorbic acid content is the main cause of the low stability of anthocyanin extracts from acerola. Food Chem., 103, 935, 2007. 

Choi, M.H., Kim, G.H., and Lee, H.S., Effects of ascorbic acid retention on juice color and pigment stability in blood orange Citrus sinensis) juice during refrigerated storage, Food Res. Int, 35, 753, 2002. 

Colorant containing annatto and Ca caseinate as carrier mixed with water to be added directly to cheese milk yielding uniform colored cheese mass Water-dispersible beadlet of p-carotene is mixed with oil to attein composition that remains stable even in presence of polyphosphates and with antioxidant action even in absence of ascorbic acid Blending carotenoid pigment and soybean fiber (wifii tomato juice) as effective ingredient for dispersion stability... 

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