Rapid Screening Procedure for Methionine Levels in Maize and Soybean

Methionine is an essential amino acid critical to human, livestock, and poultry nutrition. A microbiological method has been tested for use as a rapid, inexpensive, and reliable means of screening maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] seed for methionine concentration. Maize and soybean meal samples with various methionine contents were defatted before enzymatic proteolysis. An aliquot of each hydrolyzate was added to liquid media free of methionine, autoclaved, and inoculated with a bacteria auxotrophic for methionine. After incubation for 20 h, the turbidity of the cultures was measured and methionine concentration was calculated from standard curve data. Significant positive correlation (r = 0.74 maize; r = 0.88 soybean) was found between the microbiological and chemical determinations. These results demonstrate that the less expensive microbiological procedure would have great utility in a methionine enhancement plant breeding program.