Production of propionic acid from whey permeate by sequential fermentation, ultrafiltration, and cell recycling

This article deals with the production by fermentation of a mycostatic and aromatic food additive based on propionic acid. Membrane bioreactors have been used from laboratory scale up to pilot and industrial production plants. Due to the high cell densities achieved by the sequential recycling mode of operation, a mixed acids solution was rapidly produced from whey permeate. The sterile fermented broth obtained was subsequently concentrated at different levels by evaporation and spray drying according to the projected use. Concentrated Propionibacterium cells (200 g x L(-1) DW) were obtained from the process by periodic bleeds and could be used to good effect as cheese starters, silage preservatives, or probiotics. Propionic acid concentrations from 30 to 40 g x L(-1) were easily achieved with no residual lactose. The highest volumetric productivity was 1.6 g x L(-1) x h(-1) for total acid and 1.2 g x L(-1) x h(-1) for propionic acid with a specific productivity of 0.035 h(-1).