Purification and characterization of α ‐acetolactate decarboxylase ( ALDC ) from newly isolated Lactococcus lactis DX

BACKGROUND Diacetyl (2,3‐butanedione) is a common flavor aroma from fermented dairy products. There is a need to screen new microorganisms that can efficiently produce large amounts of diacetyl. RESULTS A new lactic acid bacterium that produced high concentrations of diacetyl was identified based on Gram staining, microscopic examination and 16S rDNA sequence analysis as Lactococcus lactis DX . Its α ‐acetolactate decarboxylase ( ALDC ) was purified using 0.45 g mL −1 ammonium sulfate precipitation, Sephacryl S‐300 and S‐200 HR and native‐ PAGE . The purified ALDC displayed a monomer structure and had a molecular mass of about 73.1 kDa , which was estimated using SDS‐PAGE . IR analysis showed that the ALDC had a typical protein structure. The optimal temperature and pH for ALDC activity were 40 °C and 6.5 respectively. The ALDC of L. lactis DX was activated by Fe 2+ , Zn 2+ , Mg 2+ , Ba 2+ and Ca 2+ , while Cu 2+ significantly inhibited ALDC activity. Leucine, valine and isoleucine activated the ALDC . CONCLUSION A strain that had high ability to produce diacetyl was identified as L. lactis DX . The difference in diacetyl production may be due to the ALDC , which is different from other ALDCs . © 2014 Society of Chemical Industry