Bromophenol Blue is a common used pH indicator dye and is with low pKa (Andrew 1995). As an acid-base indicator, bromophenol blue will lose a proton when pH of the environment around this indicator is higher than the pKa of the dye. This displacement changes the electronic distribution within the molecule and the indicator changes its color from yellow to blue (Liam, 2003). Filter paper is used to absorb bromophenol blue solution to make BPB indicator strips. After strips are exposed to the headspace of samples, bromophenol blue will react with volatile biogenic amines and change color from yellow to blue color. Colorimeters is a color measurement instruments and is used to measure the indicator strips. L*a*b* system is a cylindrical coordinate
