African Journal of Food Science Vol. 1 (1), 005-010, September 2007          
© 2007 Academic Journals

Full Length Research Paper

Characterization of two isolated lactococcal strains with respect to bacteriocin-concentrations

Babalola Olubukola O.

Department of Microbiology, Olabisi Onabanjo University, Ago-Iwoye, Ogun State, Nigeria. P.O. Box9536, UI HeadQuarters, Ibadan. E-mail: olubukola_babalola@yahoo.com.

Accepted 23 August, 2007

Abstract

Lactococcus lactis strains present in wara (local cheese), and nunu (skimmed sour milk) were isolated. These were L. lactis WO81 and N13L. Nisin assays were by agar diffusion test and turbidimetric assay. There was no successful detection of an inhibition zone with wara. However, L. lactis strain WO81 from wara was able to produce nisin. Exponential growth occurred for about 14 h after some lag phase. The optimum incubation time of 2 to 6 h was established. Nisin concentration decreased with a subsequent increase in the incubation period. The effect of inoculum size was found not to be conclusive but directional to an optimal size of 1.0% (V/V). The suitable working temperature of 30^oC and the pH value of 6 were discovered. Investigations into the phosphate sources revealed KH₂PO₄ as the best phos-phate source. A physiological link is proposed between these functions, growth and nisin concentra-tion. In the presence of sufficient glucose, growth was increased with the periodic addition of NaOH. Maximum nisin concentration was obtained when, at pH 6, the medium was buffered. In this study essentially it is noted that nisin has a lytic bactericidal mode of action.

Key words: Local cheese, ‘wara’, ‘nunu’, nisin, bacteria, bacteriocin.