Laura A. Ramallo*, Miriam D. Hubinger, and Rodolfo H. Mascheroni Effect of Pulsed Vacuum Treatment on Mass Transfer and Mechanical Properties during Osmotic Dehydration of Pineapple Slices Abstract: The influence of operating pressure during osmotic dehydration on mass transfer and mechanical properties in pineapple fruits was analyzed. Dehydration trials were performed at atmospheric pressure (OD) and by applying a vacuum pulse (VPOD), in sucrose solution at 60°Brix and 40°C for 300 min. Seven operation conditions were implemented with a vacuum pulse of 100 mbar or 250 mbar for 0, 5, 15 or 25 min at the beginning of the process. The decrease of pressure favored the solute uptake, but the water loss has not been significantly affected. No signifi- cant effect of vacuum time was observed. However, solute uptake in trials with vacuum pulse of 100 mbar was sig- nificantly higher than in OD process. In general, mechan- ical properties and shrinkage were not affected by operation conditions. Osmotic dehydration process (both OD and VPOD) originates a more resistant tissue structure than the one in fresh pineapple fruit. Keywords: vacuum impregnation, osmodehydrated pine- apple, texture, water loss, sugar gain *Corresponding author: Laura A. Ramallo, FCEQyN-Universidad Nacional de Misiones. Posadas, Misiones, Argentina, E-mail: lram@fceqyn.unam.edu.ar Miriam D. Hubinger, Department of Food Engineering, State University of Campinas (UNICAMP), Campinas, São Paulo, Brazil, E-mail: mhub@fea.unicamp.br Rodolfo H. Mascheroni, CIDCA (CONICET La Plata and UNLP) and MODIAL (FI – UNLP), La Plata, Argentina, E-mail: rhmasche@ing.unlp. edu.ar 1 Introduction During osmotic dehydration process, mass transfer kinetics and the ratio water loss/solute gain are affected by several variables: concentration and chemical compo- sition of osmotic solution, temperature, shape and size of samples and so forth. In recent years, the research has focused to an additional factor: the application of vacuum pulses during the osmotic treatment in order to increase the solute uptake in food [1, 2], to develop engineered products [3–5] and to study the kinetics changes [6–9]. Studies carried out in different fruits suggest that under some process conditions, the vacuum pulsing favors the sugar gain [1, 10–12] and in other process conditions, the application of vacuum pulse favors the water loss without affecting the solute gain [9]. Apparently, fruits porosity affects the mass transfer only at the beginning of OD [9]. Pulsed vacuum osmotic dehydration was defined as a technique which consists of dipping the fruit into an osmotic solution and applying vacuum pressure for a small period at the beginning of the osmotic treatment followed by a longer period of osmotic dehydration at atmospheric pressure [13, 14]. In particular, Shi et al. [9] found, in the pineapple dehydration at 40°C and 65°Brix, that the application of vacuum increases water loss and does not significantly affect the solid gain. One step of vacuum impregnation, followed by successive osmotic steps in sucrose solutions of increasing concentrations, at 15 and 30°C, has been tested by Barat et al. [1] in order to improve pineapple candying process. Higher water loss and lower solute gain of pine- apple samples dehydrated at 65°Brix and 30°C without vacuum pulse was found by Barat et al. [1]. Moreover, lower values of mass loss were obtained, when pineapple osmotic dehydration was preceded by a vacuum pulse com- pared to that of treatment at atmospheric pressure, espe- cially at the highest concentration and temperature [7]. In addition, some aspects of pineapple quality change during osmotic dehydration have been studied by Lombard et al. [7]. They found that L value of the color readings for samples treated with a vacuum pulse of 10 min was statistically lower than for samples dehydrated at atmospheric pressure. The effect of vacuum treatment on nutritional quality of fruit during osmotic dehydration has not been widely studied, and the results are sometimes contradictory. A study of osmo- tic dehydration of mango slices, with and without vacuum application, showed that the vacuum pulse provoked greater carotenoids retention than the traditional osmotic process [15]. Moreover, ascorbic acid content of the vacuum impreg- nated Indian gooseberry was about 39% of the fresh fruit [16]. During the osmotic dehydration process, the food undergoes important changes in thickness [17–20]. Often, shrinkage has been represented as a function of moisture content [18, 21–23]. Shrinkage is widely used in doi 10.1515/ijfe-2012-0059 International Journal of Food Engineering 2013; 9(4): 403–412 Brought to you by | Universidade Estadual de Campinas - Unicamp Authenticated | 143.106.40.121 Download Date | 1/3/14 6:08 PM