Generation of Free Amino Acids and γ-Aminobutyric Acid in Water-Soaked Soybean by High-Hydrostatic Pressure Processing

The effects of high-hydrostatic pressure processing (HPIP) on soybean cotyledon as a cellular biological material were investigated from the viewpoints of the cell structure and enzyme reaction system. Damage to cell structure was evaluated by measuring dielectric properties using the Cole-Cole arc, the radius of which decreased as pressure level increased. Results suggested that cell structure was damaged by HIPP. The distribution of free amino acids was measured after HPP (200 MPa) of soybean soaked in water or sodium glutamate (Glu) solution. HIPP resulted in high accumulation of free amino acids in water-soaked soybean, due to proteolysis. HPP of soybean in Glu solution caused higher accumulation of gamma-aminobutyric acid, suggesting that both proteolysis and specific Glu metabolism were accelerated by HPP. We concluded that HPIP partially degraded cell structure and accelerated biochemical reactions by allowing enzyme activities to remain. These events can be considered "high-pressure induced transformation" of soybean.