Effect of Plasticizer Type and Amount on Hydroxypropyl Methylcellulose-Beeswax Edible Film Properties and Postharvest Quality of Coated Plums (Cv. Angeleno) MARIA Ll. NAVARRO-TARAZAGA, † RUNGSINEE SOTHORNVIT, § AND MAR ´ IA B. P ´ EREZ-GAGO* ,† Postharvest Department, Instituto Valenciano de Investigaciones Agrarias-Fundacio ´n AGROALIMED, 46113 Moncada, Spain, and Department of Food Engineering, Faculty of Engineering at Kamphaengsaen, Kasetsart University, Kamphaengsaen Campus, Nakhonpathom 73140, Thailand The effect of the composition of hydroxypropyl methylcellulose (HPMC)-beeswax (BW) edible coatings on stand-alone film properties and on postharvest quality of coated ‘Angeleno’ plums was studied. Glycerol (G) and mannitol (M) were tested as plasticizers at two different plasticizer/HPMC ratios (100:1 and 300:1 molar basis). BW content was 20 or 40% (dry basis). An increase in G content increased film flexibility and vapor permeability (WVP), whereas an increase in M content enhanced film brittleness without affecting WVP. An increase in BW content reduced film flexibility and reduced WVP of only G-plasticized films. Coatings reduced plum softening and bleeding, but were not effective in reducing plum weight loss. At low plasticizer content, coatings reduced texture loss effectively. Low BW also lowered plum bleeding. Plasticizer type affected only ethanol and acetaldehyde contents without affecting the remaining quality parameters. Therefore, HPMC-BW coatings have the potential to extend the shelf life of plums. However, this effect depends on coating composition. Differences between coating and film performance indicate that data from stand-alone films may be used as a preliminary screening, but coating performance should be analyzed on coated fruit. KEYWORDS: Edible films and coatings; hydroxypropyl methylcellulose; plasticizer; postharvest quality; plum INTRODUCTION Plums are climateric fruits, which are suitable for cold storage for a short period depending on the susceptibility to internal breakdown and loss in texture. Some cultivars have shown an improvement in postharvest life by the use of edible coatings (1, 2). Application of edible coatings is a simple technology by which fruits and vegetables can be physically protected and have their respiration and, in some cases, ripening regulated as a passive modified atmosphere packaging (3, 4). Edible coatings can also offer a barrier to moisture transfer, reducing weight loss of the coated fruit (5). Development of edible films and coatings has been focused upon barriers containing proteins, polysaccharides, lipids, or their combination. Proteins and polysaccharides are good film- forming materials, but they are poor moisture barriers. Lipids, on the other hand, provide a better moisture barrier, but they form brittle films (6). Therefore, most of the developed edible films and coatings are combinations of a polymer matrix and a hydrophobic component. The functionality of edible coatings depends on many factors, and it has been usually predicted by using stand-alone films as a model. Factors affecting edible film performance have been extensively studied (6–9). Many of these studies elucidated how composition, preparation, and storage conditions affected film barrier and mechanical properties. These works have shown the importance of polymer cohesion on film properties and the role of different components on polymer cohesion. It has been shown that film polymer cohesion, as a result of polymer chain to chain interactions, affects film barrier and mechanical properties and can result in undesirable mechanical properties. To overcome this limitation, food-grade plasticizers are added to the film formulation. Plasticizers reduce polymer chain to chain interactions, increasing the mobility of the polymer chains and, therefore, improving film flexibility, elongation, and toughness (10). However, reduction of polymer-polymer interaction results in an increase in gas, water vapor, and solute permeability, affecting film functionality (10, 11). Plasticizer chemical structure, size, and shape influence its ability to disrupt polymer-chain bonding, including its ability * Author to whom correspondence should be addressed [telephone (34) 96 342 4000; fax (34) 96 342 4106; e-mail perez_mbe@gva.es]. † Instituto Valenciano de Investigaciones Agrarias-Fundacio ´n AGROALIMED. § Kasetsart University. 9502 J. Agric. Food Chem. 2008, 56, 9502–9509 10.1021/jf801708k CCC: $40.75  2008 American Chemical Society Published on Web 09/30/2008