Filtration of apple juice by nylon nanofibrous membranes Carlos Alberto Fuenmayor a , Solomon Mengistu Lemma b , Saverio Mannino a , Tanja Mimmo b , Matteo Scampicchio b,⇑ a Department of Food, Environmental and Nutritional Sciences, University of Milan, Via Mangiagalli, 25, 20133 Milan, Italy b Faculty of Science and Technology, Free University of Bolzano, Piazza Università 5, 39100 Bolzano, Italy article info Article history: Received 24 April 2013 Received in revised form 29 July 2013 Accepted 26 August 2013 Available online 4 September 2013 Keywords: Filtration Nanofibers Electrospinning Apple juice abstract Nylon-6 nanofibrous membranes (NFM) produced by electrospinning were applied as filter medium to clarify apple juices. The NFM exhibited good mechanical properties, lower density and higher porosity compared to commercial polyamide membranes. The filtration mechanism (initial filter, polarization and cake resistances) and the physicochemical characteristics of the filtrate (color, turbidity, acidity, anti- oxidant capacity, phenols, organic acids and sugars) were studied at pressures of 207, 276 and 345 kPa and with NFM of thickness ranging from 16 to 124 lm. NFM showed superior performance than commer- cial membranes regarding removal of turbidity, color and bitter phenolic compounds, yet maintaining the antioxidant capacity of the juice. Furthermore, NFM were able to selectively adsorb undissociated poly- phenols, like tannins. Adsorption increased at higher pressures. This work demonstrates the potential of NFM as filters for the production of clarified juices and other industrially relevant beverages. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Filtration is an important unit operation for the food and bever- age industry which can be used to clarify, stabilize, depectinize and/or concentrate liquids (such as juices, wine, beer, oils and syr- ups) by the removal of solid particles. Filters are typically made by conventional methods such as vapor or temperature-induced phase separation, stretching of melt-processed semi-crystalline polymer films, irradiation and extrusion, amongst others (Pinnau and Freeman, 2000). Electrospinning is an alternative technique for producing poly- meric membranes, that uses electric fields to spin polymer fibers with diameters ranging from hundreds to tens of nanometers, creating non-woven ‘‘fabric-like’’ mats (Gopal et al., 2006); The working principle of electrospinning is straightforward. A high voltage is applied to a polymer fluid (usually a polymeric solution) such that charges are induced within the fluid. When these charges reached a critical value, a fluid jet erupts from the droplet at the tip of the needle, resulting in the formation of a Taylor cone. Then, fibers are collected as a non-woven mesh or membrane on a collector plate that acts as the counter electrode (Ramakrishna et al., 2005). The resulting membranes show good mechanical properties, larger surface-to-mass ratio and lower density, pore sizes and resistance-to-flow than the corresponding commercial membranes (Qin and Wang, 2006; Barhate and Ramakrishna, 2007; Rama- krishna et al., 2010; Frenot and Chronakis, 2003). The application of electrospun nanofibers as filter medium can offer several advantages. First, the electrospinning process is relatively cheap. The elements required are basically three: a plastic syringe with its metal needle, a high voltage power supply (0–20 kV will suffice for most of the synthetic polymers) and a pump to deliver the polymer through the syringe needle (Huang et al., 2003). Second, nanofibrous membranes have a great surface to volume ratio. This promote, in principle, higher flow rate, lower barrier to diffusion, faster filtration time and, finally, the development of ‘one-step’ clarification processes, without the need of filter-aids and enzymatic treatments. In addition, it has been reported that nylon-6 NFM have selective adsorption capacity toward polyphenols (Scampicchio et al., 2008). The capability to remove phenols from the juice is rele- vant for the beverage industry as it can be used to selectively remove colored compounds (such as anthocyans), bitter agents (such as tannins) or haze-promoting agents (polyphenols) (Johnson et al., 1968). However, there is still limited knowledge about their use in beverages industry (Veleirinho and Lopes-da-Silva, 2009; Zhang et al., 2010) and even less on the issue of selective adsorption of molecules. Therefore, in this paper, nylon-6 NF membranes have been studied in connection with the clarification of apple juices achieved by a dead-end filtration system operating at different trans-membrane pressures. The results will demonstrate that NF membranes have better initial reactivity and greater capacity to adsorb bitter polyphenols respect conventional membranes. 0260-8774/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jfoodeng.2013.08.038 ⇑ Corresponding author. Tel.: +39 0471017210; fax: +39 0471017009. E-mail address: matteo.scampicchio@unibz.it (M. Scampicchio). Journal of Food Engineering 122 (2014) 110–116 Contents lists available at ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng