Freeze–thaw-induced Structural Destruction and Generation of γ-aminobutyric Acid in Water-soaked Soybeans

In this study, we investigated the effects of freezing and subsequent storage on γ-aminobutyric acid (GABA) accumulation in soybean (Glycine max) cotyledons. According to direct observations and an indirect analysis with Cole-Cole plots of soybeans, the membrane structure in freeze–thawed soybeans was partially destroyed and the degree of destruction increased with a decrease in the freezing temperature. GABA generation in freeze–thawed soybeans was accelerated during storage after thawing. The optimum pH for GABA generation reaction was investigated; the decrease in pH in stored soybeans was found to result in an increase in GABA generation. The higher GABA accumulation after freeze–thawing of soybeans may have been caused by the freeze–thaw-induced structural destruction, which improved substrate transfer and enzymatic reactions.