Removal of bacteria and yeast in water and beer by nylon nanofibrous membranes

Abstract

This work explores the capability of nylon-6 nanofibrous membranes prepared by electrospinning to remove bacteria and yeast cells. Nanofibrous membranes have been widely used as affinity membranes to selectively capture molecules onto the membrane surface. However, their capacity to remove microbial cells in food beverages was not yet reported. Here, dead-end filtration experiments working under constant flow-rate were tested with beer samples fortified with yeasts (Saccharomyces cerevisiae) and bacteria (Flavobacterium johnsoniae and Iodobacter fluviatilis) ranging from 1.0 × 104 to 5.1 × 108 CFU/mL. The filtration experiments resulted in resistance to flow proportional to the cells dimensions. Yeasts formed soft cakes with the lowest resistance. Conversely, it could be assumed that bacteria formed a close-pack arrangements resulting in cakes with higher density, smaller interstitial space and, thus, higher resistance to flow. Microcalorimetric experiments and plate counts demonstrated that NFM were able to completely remove S. cerevisiae from water slurries. Instead, NFM reduced the concentration of F. johnsoniae and I. fluviatilis of only 5 and 3-log cycles, respectively. However, when the two bacteria strains were mixed together, the filtration resulted in the complete removal of the cells. These results were confirmed during the filtration of beer samples inoculated with S. cerevisiae, I. fluviatilis and F. johnsoniae.