The thermal stability of lactic acid is correlated with the content of impurities in lactic acid. In case of a high content of iron, reducing sugar and other impurities, the color of lactic acid will change obviously after being heated. Particularly, when some products need to be synthesized at the high temperature (such as SSL), the adverse effect will be caused on the quality of downstream products. In fact, the thermal stability of lactic acid is one of the standards for the judgment over the quality of lactic acid products. The L-lactic acid from JMB can be heated to a high temperature of 180°C continuously for above 2 hours without change of color, and its high purity is ensured.