Possible synergistic effect between high lactate and insufficient intake of peptides caused biomass reduction during high-cell starter culture production

Abstract

Lactic starter culture production is normally subjected to the end-product inhibition on growth, which limits the biomass produced per production batch. Removal of lactate ions during the biomass production has improved the biomass production. It allows for the use of higher sugar concentration so that high biomass concentration can be obtained. Lactate removal by ion exchange resin during Lactococcus lactis NZ133 cultivation was applied as a strategy for enhancing the production of lactic starter culture biomass. At high lactose concentrations of 180 g/l, the unexpected reduction in the biomass was evident regardless of the remaining sugar in the fermentation broth. The amount of protein and proteins/polypeptides pattern profile during cultivation were investigated as protein availability was suspected to be the potential cause of biomass reduction during high cell cultivation applying the ion exchange technique. Reduction in biomass concentration, after its maximum of 26 g/l, was observed after the protein concentration was unchanged while the remaining lactose continued to be utilised. A sharp decrease in protein concentration following the addition of resin corresponded to the disappearance of the smear band of protein sized 6,512-26,625 Da when more resin was added to remove lactate. The smear band remained throughout the conventional batch cultivation period. Based on the results, insufficient supply of peptides caused by the loss through adsorption onto ion exchange resin which occurred at high lactate level was postulated as the most probable cause of the biomass reduction. The result also indicated an inefficient use of supplemented protein sources supplied in correspond to the increase in lactose concentration due to the presence of appreciable amounts of residual protein at the end of cultivation process.