3.2. Effects of pH in soaking water
Acidity of the soaking solution had a major and significant
effect on GABA content (Fig. 3). GABA content was highest at
pH 5.6 and lowest at pH 8.4, except at short germination duration
(6 or 12 h) where neutral pH gave the lowest GABA
content (Fig. 3). The two tested varieties responded differently
to pH (Fig. 3). At low pH, the two rice genotypes had
similar GABA levels but there were large and significant
differences in GABA content at neutral pH, with indica rice
having higher GABA content at all germination durations. At
a pH of 5.6 and optimal germination duration of 30 min, the
GABA content in japonica rice (1.31 g kg−1 DW) was not significantly
different (P = 0.134) from that in indica rice
(1.38 g kg−1 DW). However, under neutral conditions, with a germination
period of 30 h, the GABA content in indica rice was
34.9% higher than in japonica rice. The two varieties showed
a different response to germination duration at a high pH of
8.4 (Fig. 3).The optimal germination time for maximizing GABA
content was 6 h shorter in acidic soaking water than in neutral
soaking water (Fig. 3). A fast decline of GABA content was
found in japonica rice after germination for 36 h at pH 5.6
soaking solution.The results also showed that the GABA content
of the two cultivars at first measurement time (6 h) at pH 5.6
soaking solution were already high as compared to the
maximum attained after 30 h of germination.