Ingeniería en alimentos

Journal of Food Engineering 108 (2012) 523–531

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Journal of Food Engineering
journal homepage: www.elsevier.com/locate/jfoodeng

A convective multi-flash drying process for producing dehydrated crispy fruits
Marta Fernanda Zotarelli, Barbara Daniela Almeida Porciuncula, João Borges Laurindo ⇑
Federal University of Santa Catarina,Department of Chemical and Food Engineering, Campus Universitário-Trindade, 88040-900 Florianópolis, SC, Brazil

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The aim of this work was to evaluate the application of a convective multi-flash drying process (CMFD) to producing dehydrated and crisp fruits. To accomplish this process, samples of banana (Musa sapientum L.) or mango (Mangifera indica L.) wereheated to 60 °C by hot air, and a vacuum pulse was applied, which resulted in dehydration by a combination of convective drying and flash evaporation. Banana processed by CMFD had a moisture content of 0.293 g/g (dry basis) and aw = 0.272 after 3 h of processing. Mango had a moisture content of 0.09 g/g and aw = 0.359 after 4 h of processing. Puncture tests on fruits dehydrated by CMFD and oncommercial freeze-dried fruits showed strain–force curves with many peaks (jagged curves). For CMFD much smaller global shrinkage was observed. These results indicate that the CMFD process can be applied for producing crispy fruits and is an alternative to the freeze-drying process. Ó 2011 Elsevier Ltd. All rights reserved.

Article history: Received 14 July 2011 Received in revised form 6 September2011 Accepted 12 September 2011 Available online 21 September 2011 Keywords: Fruits Convective Multi-flash drying Freeze-drying Texturization

1. Introduction Bananas and mangoes are climacteric fruits of significant economic importance in many tropical countries. Both fruits are sources of carbohydrates, fiber and polyphenols with antioxidant capacity, such as flavonoids, anthocyanins and tannins(Pérez et al., 2011). The development of new technologies for fruit preservation and processing is necessary to reduce losses, to obtain better products and to add value. The dehydration of foods is one of the oldest techniques of preservation. The reduction of moisture content and water activity to safe levels inhibits microbial growth and enzymatic activity, increasing shelf life (Van Arsdel, 1963;Fellows, 2000; Ratti, 2001; Aguilera et al., 2003; Cano-Chauca et al., 2004). Historically, solar drying and drying with hot air (convective drying) have been the most common food drying techniques. Solar drying is cheap and traditional, but its application depends on weather conditions and requires large processing areas. Moreover, it is necessary to protect the fruits from insects and smallanimals and from contact with airborne dirt. In convective drying, it is possible to control these adverse factors and increase the average drying rate.

Abbreviations: CMFD, convective multi-flash drying; DIC, (Détente Instantanée Controlée in French) or controlled sudden decompression; P, pressure (Pa); cp, specific heat of the product during the vacuum pulse application (kJ kgÀ1 °CÀ1); mp, mass ofthe product before the application of the vacuum pulse (kg); mw, water mass (kg); Dmw, water evaporated (kg) from the product during a vacuum pulse; xw, mass fraction of water; T, temperature (°C); DT, difference between the sample ^ temperature before and after the vacuum pulse (°C); DHv , enthalpy of vaporization of water at 1500 Pa (kJ kgÀ1); t, time (s); X, moisture content (g/g) – (drybasis). ⇑ Corresponding author. Tel.: +55 48 37216402; fax: +55 48 37219687. E-mail address: joao@enq.ufsc.br (J.B. Laurindo). 0260-8774/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2011.09.014

However, the texture properties of dried fruits can be severely damaged because of strong shrinking of the solid matrix and thermal degradation. The shrinkage...