Enhancement of enterocin A production by Enterococcus faecium MMRA and determination of its stability to temperature and pH

Abstract

The growth, nutrient (total sugars, phosphorous, nitrogen and proteins) consumption and product formation by Enterococcus faecium MMRA in de Man, Rogosa and Sharpe (MRS) broth was followed in non-realkalized batch, realkalized batch and realkalized fed-batch cultures. In the latter fermentation, the growing culture was fed with a mixture of MRS medium (20 g of glucose/L) and a 400 g/L concentrated glucose. In the three cultures, a typically homolactic fermentation (only lactic acid was produced) was observed. The realkalized fed-batch culture was mainly characterized with higher biomass (2.4 g/L), lactic acid (32.5 g/L) and enterocin A (35.9 AU/mL) concentrations compared with the two batch processes. Mathematical models were developed to describe the productions of biomass, enterocin A and lactic acid in the two realkalized cultures. The growth and lactic acid production were successfully modelled with the Monod and the Luedeking and Piret models, respectively. Enterocin A was modelled by using a modified form of the Luedeking and Piret model, which includes a term for the effect of the pH drop rate on bacteriocin synthesis. Furthermore, the maximum enterocin A stability was obtained at temperatures below 100 °C, at acidic pH values and short incubation times.