Published in Scientific Papers. Series E. Land Reclamation, Earth Observation & Surveying, Environmental Engineering, Vol. II
Written by Rubén Agregán PÉREZ, Ana TORRADO AGRASAR, Lorenzo PASTRANA CASTRO, Nelson PÉREZ GUERRA
Batch productions of nisin by Lactococcus lactis subsp. lactis CECT 539 and pediocin by Pediococcus acidilactici NRRL B-5627 were firstly investigated in MRS broth and in both deproteinized diluted (DDW) and concentrated(DCW) whey. Although both strains produced the higher amounts of biomass and bacteriocin titres on MRS broth, the productions on DDW were higher than on DCW. Therefore, the following experiment was focused on the optimization of the composition of DDW medium, by using factorial experiments and empirical modelling to study the effects of total sugar (lactose), nitrogen (glycine), phosphorous (KH2PO4) and buffer (potassium hydrogen phthalate–NaOH) concentrations on nisin and pediocin productions. The increase in buffer concentration led to a decrease in the production of both bacteriocins, and the supplements with lactose, glycine and KH2PO4 did not improve nisin and pedicoin productions. Therefore, in an attempt for increasing bacteriocin production in DDW medium, both L. lactis CECT 539 and Ped. acidilactici NRRL B-5627 were grown in DDW media supplemented with lactose and four different nitrogen sources. Glycine and NH4Cl were not good nitrogen sources, but the use of high concentrations of yeast extract and Casitone highly stimulated the production of both bacteriocins. Since the use of these two complex nitrogen sources could be very expensive for bacteriocin production at a high scale, the production of bacteriocins and antibacterial factors by the two lactic acid bacteria was studied in DDW media by using re-alkalized fed-batch fermentations. These fermentations were mainly characterized with higher biomass andbacteriocin productions compared with the batch process in DDW medium and with the production of mixed acid metabolites (acetic acid, butane-2,3-diol and ethanol). We also studied the fermentation kinetics of kefir grains CIDCA AGK1 on unbuffered and buffered DDW medium. In these studies, the highest levels of free biomass, lactic acid and acetic acid were obtained in the buffered medium. Subsequently, the effect of nitrogen and phosphorous supplementation on free biomass, lactic acid and acetic acid was studied in buffered DDW medium using factorial experiments and empirical modelling. Finally, the effect of agitation and aeration on the production of the three variables was studied by using the optimized DDW medium obtained in the latter experiment.
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kefir grains
