M: Food Microbiology & Safety Physical and Antibacterial Properties of Ac ¸a´ ı Edible Films Formulated with Thyme Essential Oil and Apple Skin Polyphenols Paula J. P. Espitia, Roberto J. Avena-Bustillos, Wen-Xian Du, Bor-Sen Chiou, Tina G. Williams, Delilah Wood, Tara H. McHugh, and Nilda F. F. Soares Abstract: Thyme essential oil (TEO) and apple skin polyphenols (ASP) are natural compounds considered as generally recognized as safe by FDA, with biological effects against bacteria and fungi. This work aimed to evaluate physical and antimicrobial properties of ac ¸a´ ı edible films formulated with TEO and ASP at 3% and 6% (w/w) individually or combined at 3% (w/w) each. Physical properties studied include mechanical resistance, water vapor permeability (WVP), color, and thermal resistance. Antimicrobial activity against Listeria monocytogenes was determined using the overlay diffusion test. Addition of ASP resulted in improved mechanical properties. TEO at 6% (w/w) resulted in increased elongation. ASP films had significant higher WVP than control film. ASP films were lighter and had more red color than other films. Incorporation of ASP resulted in improved film thermal stability, whereas TEO caused rapid thermal decomposition. Presence of clusters was observed on the surface of films. Addition of ASP resulted in a smother surface, whereas addition of TEO led to the formation of crater-like pits on the film surface. Ac ¸a´ ı edible film incorporated with 6% (w/w) TEO presented the highest antimicrobial activity. However, both antimicrobials are necessary in the ac ¸a´ ı films in order to obtain edible films with suitable physical-mechanical properties. The results of the present study showed that TEO and ASP can be used to prepare ac ¸a´ ı edible films with adequate physical-mechanical properties and antimicrobial activity for food applications by direct contact. Keywords: ac ¸a´ ı, antimicrobial activity, edible film, mechanical properties, pectin, polyphenols, thermal stability, thyme essential oil Practical Application: Developed ac ¸a´ ı edible films presented antimicrobial activity against L. monocytogenes and good physical-mechanical properties, showing the potential use of ac ¸a´ ı edible films in food preservation. Introduction Consumer concerns for a healthy, nutritive, and safe diet have resulted in fast development of edible films research. Moreover, environmental issues created by plastic accumulation have con- tributed to development in this area of research. In this way, al- though recycling has been considered as an option to diminish contamination by plastic accumulation, less than 5% of plastics are recycled while the production of plastic resins is constantly growing (Sutherland and others 2010). As a result of these concerns, biopolymers have been studied as substitute materials for plastics due to their film-forming proper- ties, which are desirable for the elaboration of edible films intended as food packaging (Azeredo and others 2009). Edible films can be prepared from polysaccharides, such as pectin. Pectin is a polysaccharide that is able to form cohesive MS 20131183 Submitted 8/20/2013, Accepted 2/4/2014. Authors Espitia and Soares are with Food Packaging Laboratory, Food Technology Dept, Federal Univ. of Vic ¸osa, Av. P. H. Rolfs s/n, Campus Universit´ ario, 36570-000. Vic ¸osa, Minas Gerais, Brazil. Authors Avena-Bustillos, Du and McHugh are with Processed Foods Research Unit, Western Regional Research Center, U.S. Dept. of Agriculture, Agri- cultural Research Service, 800 Buchanan St, Albany, CA, 94710, USA. Authors Chiou, Williams and Wood are with Bioproduct Chemistry and Engineering Research, Western Regional Research Center, U.S. Dept. of Agriculture, Agricultural Research Service, 800 Buchanan St., Albany, CA, 94710, USA. Direct inquiries to author Espitia (E-mail: perez.espitia@gmail.com). and transparent films (Alves and others 2011). This polysaccharide is a structural component of cell walls, which consists primarily of partially methyl esterified poly α-d-1,4-linked galacturonic acid (homogalacturonan, “smooth” ordered regions). Pectin also has kinks of (1→2)-linked α-l-rhamnose residues as “hairy” regions due to side chains of arabinogalactan I, constituting the disordered regions (Pérez and others 2009). Moreover, pectin is an ingredient used in the food industry and is considered as generally recognized as safe (GRAS) by the U.S. Food and Drug Administration (FDA) (FDA 2012). Pectin has been used in combination with fruits to produce ed- ible films. In those studies, apple (Du and others 2008a; Mild and others 2011), tomato (Du and others 2008b), carrot and hibiscus (Ravishankar and others 2012) were used as the primary ingredi- ents for the preparation of edible films. However, to the best of our knowledge, there are no studies using ac ¸a´ ı as polymeric matrix for the development of edible films in food packaging. Recently, ac ¸a´ ı(Euterpe oleracea), a tropical fruit from Brazil, has received great attention due to the presence of bioactive com- pounds. Ac ¸a´ ı is a palm berry, round and dark purple when mature, with an average diameter of 2 cm. Ac ¸a´ ı berries are characterized by a nutty flavor with lingering metallic undertones and a creamy, as well as oily texture (Schreckinger and others 2010). According to Azeredo and others (2009), edible films produced with fruit can have sufficient mechanical and barrier properties along with the color and flavor provided by the pigments and Published 2014. This article is a U.S. Government work and is in the public domain in the USA. doi: 10.1111/1750-3841.12432 Vol. 79, Nr. 5, 2014  Journal of Food Science M903 Further reproduction without permission is prohibited