In this study, we supplied glutamic acid (Glu) into brown rice grains and allowed an enzymatic conversion from Glu to ?-aminobutyric acid (GABA) due to biosynthesis induced by high pressure (HP) treatment. The distribution of free amino acids in water-soaked brown rice grains during preservation after HP treatment at 200 MPa for 10 min was analyzed. The free amino acid distribution of HP-treated samples, just after HP treatment, showed no apparent difference from that of untreated control without HP treatment. However, during 4 days preservation at 25? after HP treatment, certain amino acids including GABA in the HP-treated samples increased with time and showed higher concentrations than those in untreated samples. To investigate the feasibility for use of HP-treated brown rice grains as a bioreactor producing GABA, Glu was supplied into brown rice grains during water soaking and applied for HP treatment. The GABA concentrations during preservation increased with the increase in the Glu concentrations in the soaking solutions. The initial GABA production rate was accelerated by HP treatment. These results provide feasibility for a novel use of HP technology to alter the metabolic pathways in a cellular biological material and to accumulate useful metabolites.
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