The influence of extrusion on loss and racemization of amino acids.
The influence of the operation conditions (temperature and residence time) of a thermic treatment on the total amount (free and protein-bound) of amino acid enantiomers of dry fullfat soya was investigated. Total amino acid content was determined using conventional ion-exchange amino acid analysis of total hydrolysates and chiral amino acid analysis was performed by HPLC after precolumn derivatization with o-phthaldialdehyde and 1-thio-beta-D-glucose tetraacetate. Contrary to corn that was investigated previously, notable racemization was detected even at lower temperatures. At 140 degrees C the ratio of the D-enantiomer was 0.87% for glutamic acid, 2.81% for serine, and 1.92% for phenylalanine; at 220 degrees C the ratios of the D-enantiomer of the above amino acids were 1.43, 4.61, and 4.68%, respectively. The concentration of several L-amino acids decreased. At 220 degrees C there was 10% less L-glutamic acid, 17% less L-serine, 5% less L-phenylalanine, 6.6% less L-aspartic, acid and 21% less L-lysine than in the control; their loss can be assigned to different degrees of L - D conversion. While nearly complete transformation of L-phenylalanine can be attributed to racemization, the main cause of the loss of L-lysine is not racemization. The treatments in the same order of magnitude resulted in the formation of more D-amino acids and greater extent of racemization of amino acids in fullfat soya than that of maize.
Csapó
J
J
Faculty of Animal Science, Institute of Chemistry, University of Kaposvár, Kaposvár, Hungary. csapo@mail.atk.u-kaposvar.hu
Varga-Visi
E
E
Lóki
K
K
Albert
Cs
C
Salamon
Sz
S
D000596:Amino Acids / Q000737:chemistry*; D005511:Food Handling; D013025:Glycine max / Q000737:chemistry*; D013237:Stereoisomerism; D013696:Temperature
D000596:Amino Acids