Purification and Characterization of Bacteriocins produced by Lactic acid bacteria isolated from fermented Milk products

摘要

Lactic acid bacteria (LAB) were isolated from domestic and commercially available curd samples. The culture supernatants were tested for antibacterial activity against Staphylococcus aureus, Listeria monocytogenes and Lactococcus cremoris. Twenty of the isolates were found to be Gram-positive cocci and remaining were Gram-positive rods. Three promising isolates (two cocci and one rod) showing antibacterial activity against various indicator organisms were chosen for further investigation. The bacteria were characterized for their morphological, physiological and biochemical characteristics. Based on the ribotyping data DFR6 and DFR8 were found to be thermobacterium sp growing at 450c. The isolates DFR13 grew over a wide PH range (3.9 - 8.5), producing acid from glucose and was negative for starch and gelatin hydrolyzing property. Bacteriocins produced by these isolates could withstand high temperature with complete inactivation or significant reduction in bacteriocin activity when treated with proteolytic enzymes such as chymotrypsin and protease. No change in activity was noticed when bacteriocin preparations were treated with amylase, catalase and lipase. Tris-tricane sodium dodecyl sulphate poly acrylamide gel electrophoresis (SDS-PAGE) of GPC purified bacteriocins indicated the molecular weight of bacteriocins to be around 5.67, 5.98 kDa for pediococcus sp (DFR6 and DFR8) and 3.75 kDa in case of Lactobacillus fermentum DFR13. Half gel activity confirmed that the antibacterial activity was due to bacteriocins comprising of protein molecules.