A Modified Amino Acid Analysis Using PITC Derivatization for Soybeans with Accurate Determination of Cysteine and Half-Cystine

Abstract

Breeding efforts to change the amino acid profile of seed protein and the assessment of genetic variation for amino acid composition among soybean germplasm resources have been hampered by lack of a rapid and inexpensive method for amino acid determination. A modified procedure presented here is partly based on a gas-phase hydrolysis and precolumn derivatization for HPLC analysis. The procedure accurately measured cysteine and half-cystine in samples. The method was also proven to be accurate using a reference protein with known amino acid composition. It is reliable and can be automated for daily analysis with a large number of samples. The method was also tested with soybean seeds harvested from a two-replicate multi-location soybean field experiment. It was found that no soybean cultivar by location interaction was significant for any of the amino acids which demonstrate that amino acid compositions were generally stable across a range of environments, and that the repeatability of the measurement itself was high. The error associated with the determination was also low as demonstrated by the analysis of variance.