Water vapor and oxygen-barrier performance of corn–zein coated polypropylene films Funda Tihminlioglu a, * , _ Isa Dog ˘an Atik a , Banu Özen b a Department of Chemical Engineering, Faculty of Engineering, _ Izmir Institute of Technology, Gülbahçe Urla 35430, _ Izmir, Turkey b Department of Food Engineering, Faculty of Engineering, _ Izmir Institute of Technology, Gülbahçe Urla 35430, _ Izmir, Turkey article info Article history: Received 6 October 2008 Received in revised form 31 July 2009 Accepted 8 August 2009 Available online 18 August 2009 Keywords: Corn–zein Polypropylene Food packaging Barrier properties Oxygen permeability Water vapor permeability abstract A novel corn–zein coating structure on polypropylene (PP) films was developed to examine its feasibility as an alternative water vapor and oxygen-barrier for flexible packaging industry. The barrier properties of the resulting films were evaluated as affected by coating formulation (solvent, corn–zein, plasticizer con- centration and plasticizer type). Corn–zein with different amounts (5% and 15%) was dissolved in 70% and 95% aqueous ethanol solution at 50 °C, respectively. Solutions of corn–zein plasticized by polyethylene glycol (PEG) and glycerol (GLY) with various levels (20% and 50%) were applied on corona-discharged- treated PP by using solvent-casting method. The significant improvements in water vapor and oxygen- barrier properties of uncoated PP films were obtained with corn–zein coating. Water vapor permeability (WVP) of the coated films decreased significantly with increasing corn–zein concentration. The applica- tion of plasticized corn–zein coating on PP films showed nearly more than three order of reduction in oxygen permeability (OP). The high water vapor and oxygen-barriers were obtained for films coated with coating formulation consisting of higher amounts of corn–zein plasticized by GLY. The statistical analysis defined the key parameters of coating formulation that had major effect on the final properties of coated PP films as corn–zein, plasticizer concentration, and plasticizer type. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction The purpose of food packaging is to preserve the quality of the food from its manufacture to consumer use. The most common quality losses are associated with water vapor and oxygen transfer. They can be blocked only by using barrier coatings on packaging materials (US Congress, Office of Technology Assessment, 1993). The conventional barrier coatings typically consist of expensive and synthetic polymers such as ethylene vinyl alcohol (EVOH) and polyvinylidene chloride (PVDC). Although these are excellent synthetic coatings, their disadvantage is related to difficulty en- tailed in their recycling due to not easy separation of coating from coated surface. It is well known that only the recycling of single component thermoplastic films is generally feasible, and the coated films containing layers of different synthetic polymers may not be recycled. Furthermore, the growing reliance on these synthetic coated packaging films has risen on number of environ- mental concerns (US Congress, Office of Technology Assessment, 1993; Tharanathan, 2003). The increased consumption of these laminated packaging films has resulted in increased environmental waste. Therefore, food industry is considering alternative packag- ing materials for coatings in terms of recyclability, reutilization, easy separation from surface, and ecological friendliness. Today, there is an increasing interest in the development of biodegradable polymers as barrier coatings for packaging industry (Chandra and Rustgi, 1998; Cutter, 2006; Reddy et al. 2003). The most important advantage of this type of coatings is an easy separation from the surface by chemical or enzymatic processes, and this provides a higher possibility for recycling. These biodegradable coating mate- rials include polysaccharides (i.e. starch, cellulose, chitosan/chitin), proteins (whey protein, corn–zein, wheat gluten, soy protein), or lipids (animal, plant-derived, etc.) (Chandra and Rustgi, 1998). Many research studies of biodegradable coating based on polysac- charides, whey proteins and lipids have been well reviewed (Cuq et al., 1998; Hong and Krochta, 2004, 2006; Hong et al., 2005; Mill- er and Krochta, 1997; Debeaufort et al., 1998). The barrier proper- ties especially to water vapor of polysaccharide-based coatings are lower compared to protein-based coatings due to specific struc- tures of proteins which confer a wider range of potential functional properties, especially high intermolecular binding potential. High molecular weight proteins are generally insoluble in water and are thus suitable to form water vapor resistant coatings (Cuq et al., 1998). Particularly among proteins, the extremely good barrier proper- ties of corn–zein proteins make them potentially useful as a barrier 0260-8774/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2009.08.018 * Corresponding author. Fax: +90 232 750 6645. E-mail address: fundatihminlioglu@iyte.edu.tr (F. Tihminlioglu). Journal of Food Engineering 96 (2010) 342–347 Contents lists available at ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng