Examination of some technological properties of lactic acid bacteria of the genera Lactiplantibacillus and Levilactobacillus isolated from spontaneously fermented sourdough. Part 2: Antimicrobial activity against saprophytic microorganisms

¹ Department of Technology of Grain, Fodder, Bakery and Confectionery Products, University of Food Technologies, 26 Maritza Blvd., 4002, Plovdiv, Bulgaria
² * Department of Biochemistry and Molecular Biology, University of Food Technologies, 26 Maritza boulevard, 4002, Plovdiv, Bulgaria
³ Department of Microbiology, University of Food Technologies, 26 Maritza boulevard, 4002, Plovdiv, Bulgaria
⁴ Department of Technology of Wine and Beer, University of Food Technologies, 26 Maritza boulevard, 4002, Plovdiv, Bulgaria

^* Corresponding author: rositsa_denkova@uft-plovdiv.com

Abstract

A positive effect of sourdough application in bread production is an extension of the shelf life of the finished bread due to inhibition of saprophytes by lactic acid bacteria (LAB) from the composition of the sourdough starters. It is important to develop new symbiotic sourdough starters that include selected lactic acid bacteria strains with symbiotic relationships and proven antimicrobial activity against saprophytic microorganisms. To achieve this, it is of paramount importance to examine the antimicrobial activity of each potential LAB strain against saprophytes. The antimicrobial activity of 4 Lactiplantibacillus strains and 2 Levilactobacillus strains against saprophytes was investigated by the agar-diffusion method with wells. Lactiplantibacillus plantarum Ph2, Lactiplantibacillus paraplantarum Ph3 and Lactiplantibacillus plantarum L1 exhibited high antimicrobial activity against Bacillus sp., while Lactiplantibacillus paraplantarum Ph5 did not suppress their growth. All four strains inhibited Aspergillus niger and Penicillium chrysogenum. Lactiplantibacillus plantarum Ph2, Lactiplantibacillus paraplantarum Ph3 and Lactiplantibacillus plantarum L1 also inhibited Aspergillus flavus, Rhizopus oryzae and Fusarium monilifirme. Both Levilactobacillus brevis strains did not inhibit Bacillus sp. and Mucor luteus, but inhibited Aspergillus niger and Fusarium moniliforme. The suppression was due to a direct antagonism between the lactic acid bacteria cells and the saprophytic cells and to a pH decrease. The antimicrobial activity of the six lactic acid bacteria strains against fungi and Bacillus sp. makes them suitable for application in the development of symbiotic starters for sourdough bread.