VTechWorks staff will be away for the Thanksgiving holiday beginning at noon on Wednesday, November 22, through Friday, November 24, and will not be replying to requests during this time. Thank you for your patience, and happy holidays!
Determination of L- and D-methionine and L- and D-valine in soy isolate and soy flour samples.
L to D isomerization of amino acids in a commercially prepared
alkali-treated food-grade soy isolate was investigated. A soy flour
product was also investigated as a control which had not been alkali treated.
Methionine and valine collected from two soy flour and two
soy isolate samples were coupled with L-leucine-N-carboxyanhydride.
If both D- and L-forms were present this would produce diastereomeric
dipeptide derivatives. The derivatives were separated by ion-exchange
chromatography using a TSM Amino Acid Analyzer. Comparison of the
sample methionine and valine dipeptide peaks to standard dipeptide
peaks revealed the presence of L-valine, L-methionine and D-methionine
in both soy flour and soy isolate samples. Methionine was substantially
isomerized in both products. D-valine was not observed in either
soy flour or soy isolate samples. Thus, isomerization of methionine
appeared to occur at a faster rate than valine. Acid hydrolysis,
toasting of soy meal, and alkaline treatment are all conditions which
may be responsible for the isomerization of methionine.