Resumo

Aims: Bacteriocins represents an ample and diverse group of ribosomally-synthesized antimicrobial peptides produced by bacteria, it kills or inhibits the growth of other pathogenic bacteria. However there have been no reports on an accurate investigation on factors influencing the bacteriocin production process by Bifidobacterium lactis. Therefore in the present study, culture conditions for bacteriocin-like inhibitory substances (BLIS) by Bifidobacterium lactis HN019 in modified Skim milk medium were optimized for their effectiveness at inhibiting Listeria monocytogenes ATCC 13932, by spot on the lawn method. Methods and results: Firstly, the effects of single factors including skim milk, cysteine and yeast extract concentration, fermentation temperature, agitation conditions and fermentation time on bacteriocin production were studied. Based on these single factor tests, a central composite design (CCD) was constructed with parameter ranges (34, 37, 40 °C), (0,5-1,0-1,5 g L-1) and (22, 24, 26 h) of temperature, yeast extract concentration and incubation time, respectively. The optimized cultivation condition were temperature (37°C), yeast extract concentration (2,0 g L-1) and incubation time (23h). Maximal bacteriocin production (inhibition zone 14.2 mm) was recorded in the presence of 1,5 g L-1 yeast extract, 34°C and 24 h incubation time, with an increase of 1,75 fold respect to the lower bacteriocin activity. The CCD results indicated that the two variables studied (Yeast extract and Temperature) have significant effect on bacteriocin production by B. lactis HN019. The quadratic effect of yeast extract was more significant than the quadratic effect of temperature. Conclusion: The CCD optimization experiments indicated the two variables (Temperature and yeast extract) studied have significant effect on bacteriocin production and showed to be a powerful tool in optimizing the culture conditions.