GABA contents in GBR were determined by using colorimetry.
One gram of GBR flour of each sample was weighed into
a plastic tube and 5 mL deionized water were added. The
mixture was oscillated and extracted for 1 h, then filtered. Half
a millilitre of the filtrate was collected to which was added
0.2 mL of 0.2 mol L−1 borate buffer (pH 9.0), 1 mL of 6% phenol
and 0.4 mL of 9% sodium hypochlorite. After intensive oscillation,
the mixture was put in boiling water for 10 min, and
then put in an ice bath for 20 min, and continually oscillated
until a blue colour appeared. Finally, 2 mL of 60% ethanol were
added to the mixture, and the sample was analyzed colorimetrically
at 645 nm wavelength. GABA content of sample was
determined by a relationship between absorption value and
standard GABA content.