Simulation of the drying curves of a meat-based product: effect of the external resistance to mass transfer Susana Simal a, * , Antoni Femenia a , Pablo Garcia-Pascual b , Carmen Rossell  o a a Department of Chemistry, University of Illes Balears, Crta. Valldemossa km 7.5, 07071 Palma de Mallorca, Spain b Food Technology Department, University Polit ecnica of Valencia, Cno. Vera s/n, 46071 Valencia, Spain Received 4 June 2002; accepted 9 September 2002 Abstract A simple mathematical model solved by the separation of variables method is proposed to simulate the drying curves of a meat- based product (sobrassada), taking into account the influence of the external mass transfer resistance. By using the experimental data of a drying curve obtained at 14 °C and 85% relative humidity (RH), both effective diffusivity and external mass transfer coefficients were simultaneously identified (2:86  10 11 m 2 /s and 3:99  10 3 m/s, respectively). The proposed model allowed the accurate simulation of the drying curves of this meat-based product at different RHs (from 70% to 85% RH) (average %var ¼ 99:8%) and even when samples had a different chemical composition (%var ¼ 98:1%) to that used to carry out the para- metric identification. Ó 2003 Elsevier Science Ltd. All rights reserved. Keywords: Meat; Sobrassada; Mass transfer; External resistance; Drying model 1. Introduction The ripening process is an important step in the manufacture of some classes of meat products. During this stage, some physical, microbiological and bio- chemical phenomena responsible for the appearance, flavour and aroma, typical of these products as well as of its conservation and sanitary safety take place (Incze, 1992; Rodr  ıguez-Rebollo, 1998). The kinetics of these reactions are affected by moisture content, as a conse- quence, the rate of water losses influence the extent of thosereactions.Furthermore,dehydrationduringripen- ing contributes to stabilising the product by decreasing the water activity value (a w ). The ability to retain water is essentially a property of the lean meat, modified by water and salts which might be added during processing (Ranken, 2000). Beside predicting the microbial or physicochemical stability of foods,theknowledgeofwatersorptionisothermsisalso very important for engineering purposes related to de- hydration (Maskan, Katatas, & Voschinin, 1998). Due to the complex composition of meat products a theo- retical prediction of sorption isotherms is not possible, and sorption data must be determined experimentally (Adam, M€ uhibauer, Esper, Wolf, & Spiess, 2000). Intheliteraturesomereviewpapersandcompilations aboutisothermsofdifferentmeatproductscanbefound (Iglesias & Chirife, 1982; Lazarides, 1990, 1991). These authors have suggested different models for the mathe- matical description of sorption isotherms. Further, Clemente, Bon, Garc  ıa-Pascual, Monle on, and Mulet (2002), Lomauro, Bakshi, and Labuza (1985) and Mo- tarjemi (1988) used different equations to model minced meat isotherms at different temperatures. These authors presented the GAB model as the best fit. Water transfer from the meat product surface to the surroundings depends on its water content and on its composition. Nevertheless, temperature and relative humidity(RH)oftheenvironmentandcharacteristicsof the boundary layer are also important. AfewreportsareavailableontheeffectofairRHon the ripening process. Lykova and Nozdrin (1993) re- ported the influence of RH on weight losses and a w of sausage-typemeatproducts:weightlosseswere18.4%at 88% RH and 20.5% at 78% RH; decrease in a w was higher at 78% RH. These authors obtained similar Journal of Food Engineering 58 (2003) 193–199 www.elsevier.com/locate/jfoodeng * Corresponding author. Tel.: 34-971-172757; fax: 34-971-173426. E-mail address: susana.simal@uib.es (S. Simal). 0260-8774/03/$ - see front matter Ó 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0260-8774(02)00369-2