Effect of pulsed-vacuum and ohmic heating on the osmodehydration kinetics, physical properties and microstructure of apples (cv. Granny Smith) J. Moreno a, ⁎, R. Simpson b, c , D. Estrada a , S. Lorenzen a , D. Moraga a , S. Almonacid b, c a Department of Food Engineering, Universidad del Bio-Bio, Casilla 447, Chillán, Chile b Department of Chemical Engineering and Environment, Universidad Técnica Federico Santa María, Casilla 110-V, Valparaíso, Chile c Centro Regional de Estudios en Alimentos Saludables, Blanco 1623 room 1402, Valparaíso, Chile abstract article info Article history: Received 16 March 2011 Accepted 24 June 2011 Editor Proof Receive Date 25 July 2011 Keywords: Osmotic dehydration Pulsed vacuum Vacuum impregnation Ohmic heating Electric filed Microstructure Apples The influence of pulsed vacuum (PVOD) and ohmic heating (OH) on the osmotic dehydration (OD) kinetics and structure of apples was evaluated. Apple cubes (1 cm 3 ) were immersed in a 65 ºBrix sucrose solution at 30, 40 and 50 °C for 300 min. The PVOD treatment was conducted at 5 kPa for 5 min, and the OH treatment was conducted at 100 V (electric field of 13 V/cm). The water loss, solid gain, a w , color and firmness were measured, and the microstructure was analyzed using electronic microscopy. The largest water loss was observed with the OD/OH treatment at 50 °C. The greatest amount of solute uptake and smallest firmness loss were obtained with the PVOD/OH treatment at 50 °C. Color differences were associated with the loss of clarity and corresponded to the transparency gain. OH treatments led to changes in the microstructure, cell walls and tissues of the apples due to the electroporation effect, which explained the increase of mass transference. Industrial relevance: The aim of this research was to determine the response of apple samples to osmotic dehydration using combined treatments of pulsed vacuum and ohmic heating. Two different technologies, vacuum and ohmic heating at mild temperatures, were used to determine and observe the mass transfer kinetics and microstructure of osmodehydrated apples. In several ohmic heating treatments, the time reduction reached 50% as compared to conventional heating. The increases of temperature, vacuum application and electroporation effect promoted the gain of osmotic solution into the tissue pores, thus reaching equilibrium in the sample with less water loss. Among the investigated conditions, the PVOD/OH treatment at mild temperatures was the best minimal processing method to preserve the fresh-like properties of the apples. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Ohmic heating (OH) is a thermal process in which the food material, which serves as an electrical resistor, is heated by an electric current. Electrical energy is dissipated into heat, which results in rapid and uniform heating. Heat is internally generated due to electrical resistance based on the intrinsic properties of electrical resistance (Salengke & Sastry, 2007). During conventional thermal processing in cans or aseptic processing systems for particulate foods, significant product quality damage may occur due to slow conduction or convection heat transfer (Zell, Lyng, Cronin, & Morgan, 2009). OH technology has gained interest because the products are of a superior quality to those processed by conventional technologies. Moreover, the ohmic heater assembly can be incorporated into a completed product sterilization or cooking process. The potential applications are numerous, including blanching, evaporation, dehydration, pasteuri- zation, and sterilization. Among the advantages of this technology are uniformity of heating and improvements in quality with minimal structural, nutritional or organoleptic changes (Vicente, Castro, & Teixeira, 2006). Wang and Sastry (1997) studied the effects of an ohmic pretreatment, and they found no changes in the moisture content of the final products. Moreover, Eliot, Goullieux, and Pain (1999a) studied the influence of precooking by OH on the firmness of cauliflower. Studies with potato cubes have suggested that ohmic treatments prevent loss of firmness when compared to conventional pretreatments (Eliot, Goullieux, & Pain, 1999b). OH provides a technology for processing particulate foods at high temperatures in a short time period without the limitations of heat transfer to particulates found in conventional treatments (Sarang, Sastry, & Knipe, 2008). In OH treatments, the moderate electric field application offers an interesting addition for enhanced diffusion via electric field treatment, and the potential of low field strength and low frequencies for plant membrane permeabilization processes increases with increasing field Innovative Food Science and Emerging Technologies 12 (2011) 562–568 ⁎ Corresponding author. Tel.: + 56 42 253173; fax: + 56 42 253066. E-mail address: jomoreno@ubiobio.cl (J. Moreno). 1466-8564/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ifset.2011.06.011 Contents lists available at ScienceDirect Innovative Food Science and Emerging Technologies journal homepage: www.elsevier.com/locate/ifset