The polymorphic transformation is an effective method to enhance the quality of glutamic acid crystal.In this study,the effect of activated carbon on the polymorphs transition of glutamic acid at the isoelectric point and its mechanism were investigated.The results showed that the wooden activated carbon ZK-200 is the most effective in shorting the time of the polymorphic transformation among all seven kinds of activated carbon experiment tested.With 1.2% activated carbon adding into the slurry at the isoelectric point,the time of polymorphic transformation was shortened to 19 min from 31 min,and the color value,transmittance and decolourization ratio were reached 0.003,83.9% and 94.6%,respectively.To reveal the mechanism of adding activated carbon on acceleration the rate of polymorphic transformation,alanine,on the behalf of impurities,was used to investigate the effect of impurity on the nucleation rate of β-nuclei and growth in the polymorphic transformation process.This novel strategy could carry out in situ polymorphic transformation at the isoelectric point,which could not only avoid the introduction of alkali solution,but also improve the crystal quality of glutamic acid.