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Composition of tomatoes and tomato products in antioxidants (WG1) page 67
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7.2 Vitamin C
Vitamin C is used as the generic descriptor for all compounds exhibiting qualitatively
the biological activity of ascorbic acid (AA). Therefore, this term refers to either or both of
the common biologically active forms : ascorbic acid (AA) and dehydroascorbic acid
(DHAA) (figure 11).
7.2.1 Chemical structure
Ascorbic acid (AA) is the enolic form of an α-ketolactone. The molecular structure
contains 2 ionizable enolic hydrogen atoms that give the compound its acidic character (pKa1
at carbon 3 = 4.17 ; pKa2 at carbon 2 = 11.57). The asymmetric carbon atom 5 allows two
enantiomeric forms, of which the L form is naturally occuring.
HO 5
CH2OH CH O O
4 1
3 2
HO OH
ascorbic acid
Figure 11 : Chemical structure of ascorbic acid and dehydroascorbic acid
7.2.2 Physico-chemical characteristics
- Molecular formula C6H8O6, Molecular weight 176.12 g/mol
- White crystals (usually plates, sometimes needles), mp 190-192°C, d 1.65
- λ max 245 nm (acid solution), 265 nm (neutral solution)
CH2OH
CH O O
O O
dehydroascorbic acid
- Solubility : soluble in water (1g in 3 ml), absolute ethanol (1g in 50 ml). Insoluble in
diethyl ether, chloroform, benzene, petroleum ether, oils, apolar solvents.
HO