Accumulation and degradation of two functional constituents, GABA and β-glucan, and their varietal differences in germinated barley grains

The changes in the contents of two functional constituents, gamma-aminobutyric acid (GABA) and (1 -> 3)(1 -> 4)beta-D-glucans (P-glucan), during germination were investigated in two malting barley varieties in order to determine the optimal conditions for accumulation and degradation of these constituents in dried barley grains after germination treatment. A time-course analysis during germination treatment revealed that the content of GABA remarkably increased in the 48 hour imbibition process and decreased in the subsequent germination process. On the other hand, P-glucan, which is known to be decomposed during malting, did not undergo substantial degradation after the 48 hour imbibition process. These findings thus indicated that it is possible to produce germinated barley grains containing these functional constituents at high levels by optimal germination treatment. A total of 43 barley varieties were surveyed for the GABA and P-glucan contents in germinated grains. Our results also indicated that there were varietal differences in the content of each ingredient. A waxy starch variety in which the contents of both P-glucan and GABA were higher than those in the other barley varieties tested, could become a promising source of the two functional constituents.