Removal of bacteria and yeast in water and beer by nylon nanofibrous membranes Solomon Mengistu Lemma, Alfonso Esposito, Marco Mason, Lorenzo Brusetti, Stefano Cesco, Matteo Scampicchio ⇑ Free University of Bozen-Bolzano, Piazza Università, 1, 39100 Bolzano, Italy article info Article history: Received 16 October 2014 Received in revised form 20 January 2015 Accepted 8 February 2015 Available online 18 February 2015 Keywords: Dead-end filtration Bacteria Yeast Electrospinning Nylon-6 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 micro- bial 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  10 4 to 5.1  10 8 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, high- er 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. john- soniae 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 con- firmed during the filtration of beer samples inoculated with S. cerevisiae, I. fluviatilis and F. johnsoniae. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Filtration is a unit operation commonly used in food processing aimed to remove suspended matter from food fluids. Generally, when a beverage is filtered through a porous membrane, solid par- ticles accumulates on the filter as a cake, whereas the fluid being filtered with a flow rate inversely proportional to the filter resis- tance (Foley, 2006; Mahdi and Holdich, 2013). This filter resistance increases with the formation of cells cake on the filter media with different morphologies in the filtration process (Ben Hassan et al., 2014; Mahdi and Holdich, 2013). Membrane filtrations have been used extensively for complete or partial removal of microbes in beer, wine and juice to achieve the highest standards of food qual- ity and safety (Lipnizki, 2010). Recently, there is a trend to prepare membranes having smaller porous size, higher surface availability and working with higher flow rates. Among others, these characteristics are desirable to speed up filtration operation, reduce pressure drops and enhance selective adsorption toward specific molecules or biological matter. Membranes prepared by electrospinning have received a great attention for this purpose as their inherent nanostructure, simple and fast processing, low cost, show a promising potential for filtration applications (Fuenmayor et al., 2014; Daels et al., 2011; Li and Xia, 2004) The working principle of electrospinning is straightforward. Briefly, a polymer solution is continuously pumped through a met- al syringe needle. When a high voltage is applied, an electrostatic repulsion between the polymer and the metal needle causes the instantaneous ejection of the polymer, which forms nanofibers col- lected as nonwoven membrane. The resulting morphology exhibits various useful characteristics for filtration applications (Barhate et al., 2006; Li and Xia, 2004; Fuenmayor et al., 2014; Gopal et al., 2007). Electrospun nanofibrous membranes (NFMs) have been widely used as affinity membranes to selectively capture molecules by binding their specific functional groups onto the membrane sur- face. For instance, NFM functionalized with amidino diethylenedi- amine were successfully applied for chelating metal ions (Kampalanonwat and Supaphol, 2010). Also, NFM functionalized with laccase were used as bioreactor for the removal of chlorophe- nols in water (Dai et al., 2013). Then, NFM were used as pre-filters for the removal of micro-particles from waste-water (Bjorge et al., http://dx.doi.org/10.1016/j.jfoodeng.2015.02.005 0260-8774/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +39 04710 17210; fax: +39 04710 17009. E-mail address: matteo.scampicchio@unibz.it (M. Scampicchio). Journal of Food Engineering 157 (2015) 1–6 Contents lists available at ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng