Quality assessment of electrohydrodynamic and microwave dehydrated banana slices Ali Esehaghbeygi * , Kianoosh Pirnazari, Morteza Sadeghi College of Agriculture, Isfahan University of Technology, 84156-83111, Isfahan, Iran article info Article history: Received 16 February 2013 Received in revised form 17 September 2013 Accepted 3 October 2013 Keywords: Shrinkage Rehydration Color Energy abstract In contrast to the inherently energy-efficient electrohydrodynamic (EHD) methods, conventional drying methods are energy intensive. In the present study, comparisons were made between banana slice samples dried by high-voltage-DC powered multiple-point-to-plate electrodes and those dried by mi- crowave (MW). For this purpose, banana slices were dried by an EHD drying system at electric field strengths of 6, 8, and 10 kV/cm and by an MW drying system at specific power levels of 9 and 18 W/g. No constant rate period was observed in the EHD; hence, the entire drying process occurred in the falling rate period, whereas the drying rates of MW-dried samples occurred at a constant rate and during the falling rate periods. Analysis of variance showed that drying method had a significant effect on drying time, rehydration ability, shrinkage, color parameters (L * ,a * ,b * , and DE), and consumed energy. The mean values of specific consumed energy for EHD and MW drying methods were 0.34 and 9.66 kJ/g, respec- tively. In terms of drying time, EHD was not fast; however, its advantages of less energy requirement and great product quality including lower shrinkage, great rehydration ability, and better appearance make it a good choice for drying banana slices. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The banana fruit comes from a tropical herbaceous plant and is normally consumed fresh; however, the qualities of fresh banana deteriorate rapidly after harvesting. Longer shelf life and significant reduction in the volume of the product are the major reasons for the popularity of dried food material. Thermal damage incurred to a product during drying is directly proportional to the temperature and time involved. Higher temperatures and longer drying times associated with conventional drying may cause serious damages to such quality attributes of the product as flavor, color, nutrients, reduction in bulk density, and rehydration ability of the dried product (Lin, Durance, & Scaman, 1998). EHD drying is a method of inducing electric wind that is generated by gaseous ions under the influence of a high-voltage electric field (Singh, Orsat, & Raghavan, 2012). The drying rate in EHD depends on the strength of the electric wind impinging on the wet material being dried to produce turbulent, vortex like motions, thereby enhancing the mass transfer rates of volatile components such as liquids (Hashinaga, Bajgai, Isoble, & Barthakur, 1999). The ionic wind velocity induced in terms of EHD set up can be calcu- lated from the following equation derived from the conservation of energy and Gaussian laws (Cross, 1979). The principal mechanism in EHD drying is based on convective heat without the need for direct heat application. This makes it useful for drying heat sensi- tive materials. The enhancement in mass transfer rate could be attributed to the electric wind induced by EHD as the main driving force. The air ions, which originated from a small region around the needle points, are accelerated by the applied electric force. Mo- mentum is transferred from the ions to the air molecules. This causes the air movement as a whole which constitutes the electric wind. The impingement of this wind on wet materials produces an impact and thus, enhances mass transfer rates of water through increased turbulence. The difference in the pressure of vapor in the ambient air and the ambient close to EHD set up, causes migrate moisture (Chen & Mujumdar, 2002). Chen, Barthakur, and Arnold (1994) investigated the effects of applying a high voltage electric field (5.25 kV/cm) on the drying characteristics of potato slices. Results showed that the drying rate of potato slices using a single point-to-plate corona discharge electrode system was enhanced by 2.1e2.5 times depending on the slice thickness compared to those dried in the ambient air and, further, that no negative effects were observed on product quality. Hashinaga et al. (1999) studied the effect of AC high voltage electric field on the drying characteristics of apple slices. Results showed * Corresponding author. Tel.: þ98 3113913473; fax: þ98 3113912254. E-mail addresses: esehaghbeygi@cc.iut.ac.ir, aeshagh@yahoo.com (A. Esehaghbeygi). Contents lists available at ScienceDirect LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt 0023-6438/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.lwt.2013.10.010 LWT - Food Science and Technology 55 (2014) 565e571