There Are Genotypic Differences for Gamma Aminobutyric Acid (GABA) Concentration in Short-Season Soybean.

Gamma aminobutyric acid (GABA) is a four-carbon, non-structural protein produced in the cytosol of plants in response to stress, via the α-decarboxylation of glutamate by the enzyme glutamate decarboxylase.  In studies, foods made from soybean (Glycine max L. Merr), with high GABA concentration, have reduced mammalian high blood pressure.  Our objective was to determine if there were genotypic differences for GABA concentration among a series of short-season soybean cultivars as well as determining the fate of GABA during soaking.  Sixteen cultivars released from 1934 to 2000, were grown in a randomized complete block design with four replications across three years at Ottawa, Canada.  Seed was harvested for yield and a sample taken to determine seed weight, protein, oil, L-glutamate (L-Glu) and GABA concentrations.  Seed from high and low GABA concentration cultivars were soaked at two different temperatures for up to 24 hours, prior to analysis for L-Glu and GABA. There were significant differences among cultivars for all parameters and significant differences among years for all parameters except L-Glu.  GABA was positively correlated with protein concentration, L-Glu and seed yield.  GABA concentration was moderately heritability (44%) and there was a threefold difference in GABA concentration between the highest and lowest cultivars.  Soaking duration significantly increased L-Glu and GABA concentration and the rate of increase was similar in both the high and low cultivars.  Soaking temperature (20 or 30^oC) did not affect L-Glu or GABA concentration.  GABA concentration can be selected in soybean cultivars and steps taken in processing to increase the concentration in foods.  Soybean cultivars with higher GABA concentration, as part of the diet, may provide a means to reduce hypertension.