For quantification of PHB, the strandard concentrations of commercial PHB at 0, 0.005, 0.01, 0.015, 0.02 and 0.025 mg/ml were hydrolyzed and analyzed using HPLC. The peak areas of the PHB-hydrolyzed product (crotonic acid) of standard concentration were linarly correlated to the PHB concentrations at R2 = 0.99. Thus, we used this concentration range of PHB product for PHB quantification. PHB content of sample was calculated from comparing the peak area of PHB sample to that of the reference PHB concentration of 0.02 mg/ml located at the middle of linear corelation as described in the defined fomular in Materiala and Methods.