Food Chemistry

1.2 Amino Acids 33

The isomers can be separated through the
sparingly soluble L-lysine sulfanilic acid
salt:

(1.65)

Fermentation with a pure culture of Bre-
vibacterium lactofermentum or Micrococcus
glutamicusproducesL-lysine directly:

(1.66)

1.2.5.4 Methionine.............................................

Interaction of methanethiol with acrolein pro-
duces an aldehyde which is then converted to

the corresponding hydantoin through aBucherer
reaction. The product is hydrolyzed by al-
kaline catalysis. Separation of the resultant
racemate is usually not carried out since the
D-form of methionine is utilized by humans via
transamination:

(1.67)

1.2.5.5 Phenylalanine

Benzaldehyde is condensed with hydantoin,

then hydrogenation using a chiral catalyst gives

a product which is about 90%L-phenylalanine:

(1.68)

1.2.5.6 Threonine..............................................

Interaction of a copper complex of glycine with

ethanal yields thethreoanderythroisomers in the

ratio of 2:1. They are separated on the basis of

their differences in solubility:

(1.69)

D,L-threonine is separated into its isomers

through its N-acetylated form with the help of an

acylase enzyme.

Threonine is also accessible via microbiological

methods.

1.2.5.7 Tryptophan.............................................

Tryptophan is obtained industrially by a varia-

tion of theFischer indole synthesis. Addition

of hydrogen cyanide to acrolein gives 3-cyano-

propanal which is converted to hydantoin through

aBuchererreaction. The nitrile group is then