Nisin-producing microorganisms and their implementation in brewers' wort

Abstract

Nisin is a bacteriocin, which is capable of eliminating more than 90% of all potential beer spoilage Gram-positive bacteria. Hence, the implementation of nisin-producing cultures into the brewing process needs to be evaluated systematically. In this work, the genetic relationships and properties, as well as the reactions of four strains of Lactococcus lactis ssp. lactis, known to be capable of producing nisin (NCIMB 8780, 8586, 701402 and 701403), and seven isolated strains of the same species found in the beverage environment (TUM 575, 8947, 8127, 8446, 8673, 8973 and 8872), were tested under typical brewery conditions. As in previous work, it was found, that all of the tested strains could be genetically differentiated via PCR-(GTG)5. In addition, the absence of the genes HorA, HorC and ORF5 indicated that all strains were sensitive to hop components. The agar diffusion assay test proved to be the most reliable method to precisely determine different nisin concentrations. Nisin formation, acid formation and the reproduction rates of the organisms were tested subsequently in various brewery relevant culture media such as MRS, first wort (unhopped) and wort (hopped). MRS provided the best environment for bacterial growth and hence acid and nisin production. The four NCIMB strains, which were the only ones capable of producing nisin under the named conditions, were chosen for study with regards to their tolerance to specific compounds found in the brewery environment. The strains NCIMB 8780 and 8586 produced comparatively higher amounts of nisin and were more tolerant to hop bitterness, ethanol, high gravity and low extract conditions. The growth rates, acid production and nisin production of all strains decreased with increasing bitter units and ethanol content. The optimum extract concentration was 5–10°P. Copyright © 2015 The Institute of Brewing & Distilling