Suitability of novel galactomannans as edible coatings for tropical fruits Miguel A. Cerqueira a , Álvaro M. Lima b , José A. Teixeira a , Renato A. Moreira c , António A. Vicente a, * a IBB – Institute for Biotechnology and Bioengineering, Centre of Biological Engineering, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal b Departamento de Bioquímica e Biologia Molecular, Federal University of Ceará, Campus do Pici, CEP 60451-970 Fortaleza, CE, Brazil c Centro de Ciências da Saúde, Universidade de Fortaleza, Av. Washington Soares, 1321 Bairro Edson Queiroz, 60811-905 Fortaleza, CE, Brazil article info Article history: Received 9 August 2008 Received in revised form 25 March 2009 Accepted 4 April 2009 Available online 16 April 2009 Keywords: Edible coatings Edible films Galactomannans Wettability Tropical fruits abstract The main objective of this work was to determine the optimal composition of edible coatings in view of their application to extend the shelf life of several tropical fruits. Coatings constituted by galactomannans from different sources (Caesalpinia pulcherrima and Adenanthera pavonina) and glycerol were character- ized as coatings for five tropical fruits: acerola (Malpighia emarginata), cajá (Spondias lutea), mango (Mangifera indica), pitanga (Eugenia uniflora) and seriguela (Spondias purpurea). The surface properties of the five fruits were determined and different aqueous galactomannan solutions (0.5%, 1.0% and 1.5%) with glycerol (1.0%, 1.5% and 2.0%) were tested for their wettability on fruits. For the solutions hav- ing a better wettability, films were casted and water vapour permeability, oxygen permeability, carbon dioxide permeability, tensile strength and elongation at break were determined. Taking into account the surface and permeability properties of the obtained films, four compositions were selected as the best coatings to the studied fruits: acerola – 0.5% of A. pavonina galactomannan and 1.0% of glycerol; cajá – 1.0% of A. pavonina galactomannan and 1.0% of glycerol; mango and pitanga – 1.5% of A. pavonina galac- tomannan and 1.0% of glycerol; and seriguela – 0.5% of C. pulcherrima galactomannan and 1.5% of glycerol. For the coating, the values of the measured properties were as follows: wettability ranged from 36.33 ± 3.39 to 26.45 ± 4.58 mN  m 1 ; water vapour permeability ranged from 4.89 ± 0.11 to 6.25 ± 0.20  10 11 gm 1 s 1 Pa 1 ; oxygen permeability ranged from 0.31 ± 0.01 to 0.99 ± 0.13  10 15 g m (Pa s m 2 ) 1 ; carbon dioxide permeability ranged from 28.81 ± 3.08 to 61.19 ± 1.44  10 15 gm (Pa s m 2 ) 1 ; tensile strength ranged from 2.56 ± 0.15 to 3.96 ± 0.43 MPa; and elongation at break ranged from 28.26 ± 4.53% to 46.36 ± 2.29%. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction During the last decades, there has been an increasing demand for fresh fruits and vegetables forcing the food industry to develop new and better methods for maintaining food quality and extending shelf life. Great losses (from 20% to 80%) in the quality of fresh fruits occur from harvesting to final consumption and the fruits short shelf life is an important drawback concerning distribution chains. On the other hand, consumers around the world demand food of high qual- ity, without chemical preservatives and with extended shelf life. As a consequence, an increased effort has been made to discover new natural preservatives and antimicrobials (Chien et al., 2007). Packaging plays a decisive role in the improvement of fruits’ shelf life and new packaging materials are being developed, most of them are derived from renewable resources (Lin and Zhao, 2007). Edible coatings act by creating a modified atmosphere sur- rounding the commodity, similar to that achieved by controlled or modified atmospheric storage conditions. The modified atmo- sphere created by edible coatings protects the food from the mo- ment it is applied until it reaches the final consumer (Diab et al., 2001; Durango et al., 2006; Ribeiro et al., 2007). Several researchers studied the application of coatings in fruits such as apples (Rojas-Grau et al., 2007), strawberries (Mali and Grossmann, 2003; Tanada-Palmu and Grosso, 2005; Ribeiro et al., 2007), mango (Srinivasa et al., 2002; Chien et al., 2007; Dang et al., 2008) and kiwi (Xu et al., 2001). Polysaccharide-based coat- ings are colourless and have an oil-free appearance, and can be used to increase the shelf life of fruits, vegetables, shellfish or meat products to avoid dehydration, and to reduce the oxidative rancid- ity and darkening of the surface to some extent. Other characteris- tics that make them attractive are their transport properties (permeability to CO 2 ,O 2 and water vapour), the reduction of mate- rials weight loss and the reduction of the microbial spoilage of the fruits (Petersen et al., 1999; Dang et al., 2008). However, the effec- tiveness of edible coatings for fruits preservation depends, in a first stage, on the control of the wettability of the coating in order to ensure a uniformly coated surface. Other factors also affect the effectiveness of the coating, such as transport (permeability) and mechanical properties; these must also be considered in order to: 0260-8774/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2009.04.003 * Corresponding author. Tel.: +351 253 604 419; fax: +351 253 678 986. E-mail address: avicente@deb.uminho.pt (A.A. Vicente). Journal of Food Engineering 94 (2009) 372–378 Contents lists available at ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng