CHARACTERIZATION OF DIACETIN-B, A BACTERIOCIN FROM LACTOCOCCUS-LACTISSUBSP LACTIS BV DIACETYLACTIS UL720

Fourteen Lactococcus lactis strains showing inhibitory activity agains t Listeria innocua SICC 4202 were isolated from different French raw m ilks and raw milk cheeses and screened for bacteriocin production by t he triple layer method under conditions that eliminate the effects of lactic acid and hydrogen peroxide. Three bacteriocinogenic strains (tw o Lactococcus lactis subsp, lactis by. diacetylactis UL719 and UL720 a nd one Lactococcus lactis subsp. lactis UL730) were selected for their high capacity to inhibit the growth of various food pathogens, includ ing Listeria monocytogenes, Staphylococcus aureus, and clostridial str ains. The inhibitory compounds from these three strains are inactivate d by selected proteases, indicating their protein nature. They retaine d their antibacterial activity after heat treatments of 100 degrees C for 60 min and 121 degrees C for 20 min, and in the pH range from 2 to 11. The bacteriocin diacetin B produced by strain UL720 has been puri fied by a pH-dependent adsorption-desorption procedure, followed by re verse-phase high performance Liquid chromatography, with a yield of 1. 25% of the original activity. Mass spectrometry analysis indicates tha t the pure peptide has a molecular mass of 4292.32 or 4490.28 Da, whil e amino acid sequencing allowed the identification of the primary stru cture of the bacteriocin composed of 37 amino acid residues. The struc ture of the peptide did not show similarity with ether known bacterioc ins from lactic acid bacteria.