2009_Book_FoodChemistry

32 1 Amino Acids, Peptides, Proteins
industrial processes for a number of amino
acids.
A synthetic procedure starts with caprolactam,
which possesses all the required structural features,
except for the α-amino group which is introduced
in several steps:
1.2.5.1 Glutamic Acid
Acrylnitrile is catalytically formylated with
CO/H 2 and the resultant aldehyde is transformed
through a Strecker reaction into glutamic acid
dinitrile which yields D,L-glutamic acid after
alkaline hydrolysis. Separation of the racemate
is achieved by preferential crystallization of
the L-form from an oversaturated solution after
seeding with L-glutamic acid:
(1.63)
(1.60)
A fermentation procedure with various selected
strains of microorganisms (Brevibacterium
flavum, Brev. roseum, Brev. saccharolyticum)
provides L-glutamic acid in yields of 50 g/l of
fermentation liquid:
Separation of isomers is done at the α-amino
caprolactam (Acl) step through the sparingly soluble
salt of the L-component with L-pyrrolidone
carboxylic acid (Pyg):
(1.64)
1.2.5.2 Aspartic Acid
(1.61)
Aspartic acid is obtained in 90% yield from fumaric
acid by using the aspartase enzyme:
1.2.5.3 Lysine
(1.62)
More elegant is selective hydrolysis of the
L-enantiomer by an L-α-amino-ε-caprolactamase
which occurs in several yeasts, for example
in Cryptococcus laurentii. The racemization
of the remaining D-isomers is possible
with a racemase of Achromobacter obae.
The process can be performed as a one-step
reaction: the racemic aminocaprolactam is
incubated with intact cells of C. laurentii
and A. obae, producing almost 100% L-
lysine.
In another procedure, acrylnitrile and ethanal
react to yield cyanobutyraldehyde which is
then transformed by a Bucherer reaction
into cyanopropylhydantoin. Catalytic hydrogenation
of the nitrile group, followed
by alkaline hydrolysis yields D,L-lysine.