L-dehydroascorbate

L-dehydroascorbic acid, are active forms of the vitamin. However, once the dehydro form is further oxidized to diketogiuconic acid, no vitamin C activity is retained. The thermal half life of dehydroascorbic acid is less than 1 minute at lOO C (pH 6), and 2 minutes at 7O C Vitamin C is also... 

Compounds that can scavenge radicals are also referred to as antioxidants. The best known anti-oxidants are vitamin C and vitamin E. Vitamin C is L-ascorbate (7.8), a good reducing agent that prevents oxidation of other molecules. The oxidized form of L-ascorbate is L-dehydroascorbic acid (7.9). Vitamin E is a mixture of a-, [3-, y-, and 8-tocopherol (7.10a-d). Of these four compounds, a-tocopherol is the most effective. Vitamin E is lipid-soluble and has the ability to disrupt the chain reaction during lipid peroxidation (see Chapter 2, Section 1.9). 

The difference is two hydrogens. L-ascorbic acid is the reduced form of this vitamin L-dehydroascorbic acid is its oxidized form. The L indicates that each has the L configuration at carbon 5. 

Antioxidant in vivo (diabetic rat) scavenges DPPH (weak) [>L Dehydroascorbate, T lysosomal stability]... 

We thank Paul Seib for the samples of D-ert/thro-dehydroascorbic acid and 6-bromo-6-deoxy-L-dehydroascorbic acid. 

L- /ireo-Hex-2,3-diulosic acid y-lactone (L-dehydroascorbic acid)... 

L-Dehydroascorbic acid, a derivative with potent vitamin activity in vertebrates, was inactive in our bioassay when it was mixed with hot diet prior to gelation. However, when we repeated the bioassay by applying dehydroascorbic acid to the surface of the gelled diet, the... 

Na ascorbate, Ca ascorbate, l-dehydroascorbic acid active, D-isoascorbic acid inactive... 

L-ascorbic acid, D-isoascorbic acid, and L-dehydroascorbic acid inhibited progeny by producing diet nutritionally deficient in protein (browning)... 

Figure 4.18 Early rationalisation of L-ascorbic acidf L-dehydroascorbic acid interconversion...

Although L-ascorbic acid does not have a carboxylic acid group, it is an acidic compound because the of the C-3 OH group is 4.17. L-Ascorbic acid is readily oxidized to L-dehydroascorbic acid, which is also physiologically active. If the lactone ring is opened by hydrolysis, all vitamin C activity is lost. Therefore, not much intact vitamin C survives in food that has been thoroughly cooked. Worse, if the food is cooked in water and then drained, the water-soluble vitamin is thrown out with the water ... 

The principal compound with vitamin C activity that is found naturally is L-ascorbic acid. r-Ascorbic acid is readily oxidized in solution to L-dehydroascorbic acid, which means that methods for the determination of total vitamin C content require quantification of both forms. Acids are normally used for extraction to protect vitamers from degradation and to precipitate... 

L-dehydroascorbic acid are physiologically active and are found together in most body fluids. 

Scheme 8.13. A representation of the oxidation of L-ascorbic acid (vitamin C) to L-dehydroascorbic acid and then to diketogulonic acid.

L-ascorbic acid (AA) and L-dehydroascorbic acid (DHAA) are the two main C vitamers occurring in nature [1]. In food analysis, the valuation of the vitamin C total content should account for both forms, since DHAA is readily reduced to AA in the animal body. D-isoascorbic acid (D-IAA), also known as erythorbic acid or D-araboascorbic acid, has analogous reductive properties but only 5% of the antiscorbutic activity of L-AA this epimer is a by-product of vitamin C, and is approved within the European Community as an antioxidant additive [62]. The capability of LC to distinguish the two ascorbic acid isomers and their primary oxidation products is very useful for analyzing processed foods. Forms used for supplementation are AA, sodium-, calcium-, or potassium-L-ascorbate and L-ascorbyl 6-palmitate [4]. 

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