Production of free amino acids and gamma-aminobutyric acid by autolysis reactions from wheat bran.
To find added value for wheat-milling byproduct, an approach for producing free amino acids and gamma-aminobutyric acid (GABA) was examined. Milled whole grain, bran, shorts, red dog, and 60% extracted flour all released amino acids using a water-soaking treatment. Little difference was found in amino acid production yield from whole grain between the soft and hard wheat cultivars investigated. Among the milled fractions, shorts produced the largest amount of total amino acids followed by bran, red dog, and 60% extracted flour in decreasing order. From the byproduct fraction (mixture of bran and shorts), leucine (Leu), arginine (Arg), valine (Val), lysine (Lys), glutamine (Gln), phenylalanine (Phe), isoleucine (Ile), and GABA were produced at 486, 421, 316, 329, 321, 279, 227, and 118 mg/100 g, respectively, in 120 h at 40 degrees C. Optimal pH for the byproduct fraction was 3.5-5.0 for alpha-amino acids and 5.5 for GABA. The production levels rose with increasing temperature up to 40-50 degrees C for alpha-amino acids and up to 40 degrees C for GABA. The yield of all amino acids increased in the experimented period until 120 h except for aspartic acid (Asp) and asparagine (Asn). Thus, wheat-milling byproducts have the potential to become effective materials for developing foods enriched in branched-chain amino acids (BCAA), Arg, Lys, Gln, Phe, and GABA.