PRODUCTION OF A MIXTURE OF ANTIMICROBIAL ORGANIC-ACIDS FROM LACTOSE BY COCULTURE OF BIFIDOBACTERIUM-LONGUM AND PROPIONIBACTERIUM-FREUDENREICHII

The antimicrobial activities of standard solutions of three organic ac ids (lactic, acetic, and propionic acids) were compared using Micrococ cus luteus, Pseudomonas sp. and Staphylococcus aureus as test microorg anisms. At the same concentrations of the undissociated form, the anti microbial activities of acetic and propionic acids were higher than th at of lactic acid, irrespective of test microorganisms. In a single cu ltivation of Bifidobacterium longum, a mixture of lactic (17 g/l) and acetic (20 g/l) acids was produced from 50 g/l lactose and its antimic robial activities against M. luteus, Pseudomonas sp., and S. aureus co rrespond to that of 32, 19, and 25 g/l of acetic acid, respectively. T o increase the total antimicrobial activity, a co-culture of B. longum and Propionibacterium freudenreichii, in which lactic acid produced o nce from lactose by B. longum was converted to acetic and propionic ac ids by P. freudenreichii, was done using TPY medium containing commerc ially available peptones as a nitrogen source. By the sequential conve rsion of lactose using the two microorganisms, the culture supernatant containing a mixture of acetic (27 g/l) and propionic (13 g/l) acids without lactic acid was produced. The antimicrobial activities of the mixture against nl. luteus, Pseudomonas sp., and S. aureus were 35, 30 , and 26 g/l as a concentration of acetic acid, respectively, higher t han that obtained in the cultivation of B. longum alone. When the medi um containing an enzymatic hydrolyzate of whey proteins with a proteas e was used in the co-culture of B. longum and P. freudenreichii, the c ulture supernatant containing the mixture of organic acids was also ob tained in the same manner as the co-culture using TPY medium and the a ctivities were 43, 29, and 29 g/l as a concentration of acetic acid fo r M. luteus, Pseudomonas sp. and S. aureus, respectively.