Effect of apparent density of sliced food particles on the efficiency of pulsed electric field treatment H. Mhemdi a , N. Grimi a , O. Bals a , N.I. Lebovka a, b, ⁎, E. Vorobiev a a Université de Technologie de Compiègne, Département de Génie des procédés industriels, Unité Transformations Intégrées de la Matière Renouvelable (UTC/ESCOM, EA 4297 TIMR), Centre de Recherche de Royallieu, B.P. 20529-60205 Compiègne Cedex, France b Institute of Biocolloidal Chemistry named after F.D. Ovcharenko, NAS of Ukraine, 42, blvr. Vernadskogo, Kyiv 03142, Ukraine abstract article info Article history: Received 19 July 2012 Accepted 24 December 2012 Editor Proof Receive Date 14 February 2013 Keywords: Electroporation Potato slices Pulsed electric fields Electrical conductivity Disintegration index Apparent density This work discusses the effects of pulsed electric field (PEF) (electric field strength, E, 100–1000 V; pulse duration, t p , 100 μs) on disintegration of potato slices treated between parallel plate electrodes by using a laboratory compression chamber equipped with a PEF-treatment system. The apparent density of slices (bed of particles), ρ, was varied within 0.313 g/cm 3 and 1 g/cm 3 . The electrical conductivity σ(ρ) of the packing of slices versus volume fraction of particles ϕ was approximated by the percolation law σ ∝ (φ −φ c ) t , where ϕ c ≈ 0.290, t =t i ≈ 0.46 and t =t d ≈ 1.39 for the intact and completely damaged tis- sues, respectively. The impact of electric field strength and apparent density of slices on PEF-induced dam- age kinetics was studied. The more accelerated kinetics of damage was observed for more dense packing of slices. The approximated relation between the applied, E, and effective, E e , electric field strengths account- ing for the σ(ρ) dependence was derived. Industrial relevance: The practical applications of PEF treatment (e.g., pressing, drying, extraction, etc.) demand operations with slices of food particles. In this study, research towards the electroporation effi- ciency of PEF applied to the porous packing of sliced food particles is provided. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction Nowadays, the pulsed electric fields (PEF) become more and more popular in different applications for processing of bio-tissues, food or ag- ricultural products (Knorr, Engel, Vogel, Kochte-Clemens, & Eisenbrand, 2008; Vorobiev & Lebovka, 2010). PEF application at moderate electric field strengths E of 0.5 to 1 kV/cm and treatment times between 10 −4 and 10 −2 s allows effective disintegration (electroporation) of cell membranes (Lebovka & Vorobiev, 2010) with preservation of the fresh quality of products, e.g., bioactive compound purity, colour, texture, aroma, flavour, and nutrients (Odriozola-Serrano, Aguilo-Aguayo, Soliva-Fortuny, & Martin-Belloso, 2013). The different examples of ac- celeration of the mass transfer processes (Donsi, Ferrari, & Pataro, 2010; Porras-Parral, Miri, Bakalis, & Fryer, 2012), pressing (Lebovka, Praporscic, & Vorobiev, 2004), drying (Ade-Omowaye, Angersbach, Taiwo, & Knorr, 2001), freezing (Jalte, Lanoiselle, Lebovka, & Vorobiev, 2009), extraction (Loginova et al., 2011a, 2011b) and osmotic dehydra- tion (Amami, Khezami, Vorobiev, & Kechaou, 2008) were already reported. PEF-treatment requires a rather low power consumption, typ- ically lying within 1–15 kJ/kg (Vorobiev & Lebovka, 2010), and it defines the unique industrial attractiveness of this approach. The practical implementations of PEF-assisted technologies were realised in different ways by application of PEF to the whole samples of agricultural species (Bluhm et al., 2004; Grimi, Mamouni, Lebovka, Vorobiev, & Vaxelaire, 2010) or mechanically fragmentized material, e.g. sugar beet slices, apple mash (Grimi, Praporscic, Lebovka, & Vorobiev, 2007). The mecha- nisms of electroporation were better studied for constant operation conditions and simple systems, e.g., biological membranes, suspensions of cells and single pieces of agricultural tissues (Lebovka & Vorobiev, 2010). However, more practical situations of PEF application with non-constant operation conditions or with complex samples (e.g., geo- metrically irregular shape, porous packing of slices, etc.) are still unclear and demand more thorough investigations in future. The aim of this study was to evaluate the electroporation efficiency of pulsed electric field treatment applied to the porous packing of sliced food particles. The potato tissue was chosen as a model food tissue. The relations between apparent density of slices, effective electrical conduc- tivity of packing and effective electric field were established. 2. Materials and methods 2.1. Plant material Commercial potatoes (Marabel) of good and uniform quality were purchased at the local supermarket (Compiegne, France) Innovative Food Science and Emerging Technologies 18 (2013) 115–119 ⁎ Corresponding author at: Institute of Biocolloidal Chemistry named after F.D. Ovcharenko, NAS of Ukraine, 42, blvr. Vernadskogo, Kyiv 03142, Ukraine. Tel.: +380 44 4240378; fax: +380 44 4248078. E-mail addresses: lebovka@gmail.com (N.I. Lebovka), Eugene.Vorobiev@utc.fr (E. Vorobiev). 1466-8564/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ifset.2012.12.008 Contents lists available at SciVerse ScienceDirect Innovative Food Science and Emerging Technologies journal homepage: www.elsevier.com/locate/ifset