2009_Book_FoodChemistry

17.1 Vegetables 781
to ketoglutarate in the Krebs cycle:
The important precursors of onion flavor, the
S-alkylcysteine sulfoxides, are formed as follows:
(17.3)
(17.1)
4-Methyleneglutamic acid (Table 17.5: XXXI) is
formed from pyruvic acid:
2,4-Diaminobutyric acid and some other
compounds are derived from cysteine (cf. Reaction
17.4).
The aspartic acid semi-nitrile formed initially
can be decarboxylated to β-amino propionitrile
which, just as its γ-glutamyl derivative, is
responsible for osteolathyrism in animals.
Hydrolysis of the semi-nitrile yields aspartic acid,
hydrolysis and reduction yield 2,4- diaminobutyric
acid, the oxalyl derivative of which, like
oxalyldiaminopropionic acid, is a human neurotoxin.
The main symptoms of neurolathyrism
are paralysis of the limbs and muscular rigidity.
2,4-Diaminobutyric acid can be converted via the
aspartic acid semialdehyde into 2-azetidine carboxylic
acid (XXI), which occurs, for example,
in sugar beets (Table 17.5).
(17.2)
(17.4)