Development of novel dead-end filtration strategy for isolation of pullulan broth

Abstract

Pullulan, a natural extracellular polysaccharide, is widely used in food and related industries, cosmetics, and pharmaceuticals. The high viscosity of its fermentation broth poses significant challenges for efficient separation, making the process both difficult and time-consuming. In this study, cross-flow membrane filtration was first applied to separate a two-fold diluted broth (feed solution), where membranes with pore sizes ranging from 150 kDa to 0.8 μm rejected over 99 % of cells and approximately 50 % of pullulan. This phenomenon was attributed to higher shear forces increasing pullulan particle size in solution, thereby reducing its recovery rate. To address this limitation, a dead-end filtration strategy was developed using a 1–3 μm filtration medium with 1 % filter aid. During concentration-mode filtration, fouling mechanisms in the first stage showed indistinct differences between standard and intermediate blocking, while the second stage exhibited unclear distinctions between complete and intermediate blocking. A favorable membrane regeneration strategy was identified: sequential washing with fresh water followed by detergent powder. This method achieved 99.54 % biomass removal and a pullulan recovery rate of 90.67 %. Overall, the dead-end filtration strategy presents a novel approach for separating high-viscosity biopolymers, offering both efficiency and practicality for industrial applications.