Properties of fish skin gelatin film incorporated with seaweed extract Saowapa Rattaya a , Soottawat Benjakul a, * , Thummanoon Prodpran b a Department of Food Technology, Faculty of Agro-Industry, Prince of Songkla University, 15 Knachanawanich Road, Hat Yai, Songkhla 90112, Thailand b Department of Material Product Technology, Faculty of Agro-Industry, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand article info Article history: Received 15 January 2009 Received in revised form 19 April 2009 Accepted 25 April 2009 Available online 5 May 2009 Keywords: Gelatin film Seaweed extract Physical properties Mechanical properties abstract Fish skin gelatin films incorporated with 6% oxygenated seaweed (Turbinaria ornata) extract (based on protein content) with pHs 9 or 10 were prepared and characterized in comparison with the control film (without seaweed extract). Films incorporated with seaweed extract at both pHs exhibited the higher elongation at break (EAB) than the control film (p < 0.05). However, no differences in tensile strength (TS) and transparency between films without and with seaweed extract were observed (p > 0.05). Water vapor permeability (WVP), and film solubility decreased as seaweed extract was incorporated, regardless of pH (p < 0.05). This was associated with the formation of non-disulfide covalent bond in the film matrix, most likely induced by the interaction between oxidized phenols in seaweed extract and gelatin mole- cules. Coincidentally, the second transition temperature of gelatin film shifted from 170.54 to 178.36 °C when incorporated with 6% seaweed extract at pH 10. Film without seaweed extract had smooth surface while the rougher surface was noticeable in film incorporated with seaweed extract for both pHs. Thus, the addition of seaweed extract had the impact on the property of fish skin gelatin film, most likely due to the enhanced formation of protein cross-links. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Plastic packaging or synthetic films has been widely used, due to their good mechanical properties and effectiveness as a barrier to oxygen and water (Gómez-Estaca et al., 2009; Gómez-Guillén et al., 2009). However, most synthetic films are petrochemical- based and non-biodegradable, leading to environmental pollution and serious ecological problems (Tharanathan, 2003). Therefore, edible film from natural polymer has become an ecologically important alternative to the film from commonly used synthetic polymer (Piotrowska et al., 2008). Edible films can enhance food quality by acting as moisture, gas, aroma and lipid barriers, provid- ing protection to a food product after the primary package is opened. Furthermore, such films are biodegradable and can even be eaten with food, which will reduce pollution of traditional non-biodegradable plastic films (Kim and Ustunol, 2001). Edible films can be made from natural polymers including, proteins, poly- saccharides, lipids or the combination of these components (Thara- nathan, 2003). Protein-based films generally exhibit the poor water barrier property. However, films composed of lipids are more moisture resistant (Gontard et al., 1994). Gelatin obtained by partial degradation of collagen has gained more attention as a new material for edible films (Jongjareonrak et al., 2006; Gómez-Guillén et al., 2009). With the restriction of uses of gelatin from land animals, fish gelatin is acceptable for Is- lam, and can be used with minimal restrictions in Judaism and Hin- duism. Nevertheless, gelatin from marine sources showed the lower functional properties than that of mammalian (Leuenberger, 1991). Chemical and physical treatments can be applied to modify the polymer network through cross-linking of the polymer chains (Cao et al., 2007). Chemical cross-linking agents and enzyme used include gossypol, formaldehyde, glutaralaldehyde (Marquie et al., 1995; de Carvalho and Grosso, 2004; de Carvalho et al., 2008), and transglutaminase (Mariniello et al., 2003). Nevertheless, some cross-linking agents have the toxicity and high cost (Bigi et al., 2002; Cao et al., 2007). Therefore, a natural cross-linking agent with no toxicity is of great interest for improving the properties of films, especially protein based film. Seaweeds or marine macroalgae are potential renewable re- sources in the marine environment. About 6000 species of sea- weeds have been identified and are grouped into different classes including green (Chlorophytes), brown (Pheophytes) and red (Rho- dophytes) algae (Abugoch et al., 2003). Total global seaweed pro- duction of the world in the year 2004 was greater than 15 million metric tones (FAO, 2006). However, algae grown in Thai- land are still underutilized. Only small portion has been used as food, animal feed, fertilizers, and for the production of hydrocol- loids (Aungtonya and Liao, 2002). Seaweed extracts are considered to be a rich source of phenolic compounds (Athukorala et al., 2003; Heo et al., 2005). Strauss and Gibson (2004) reported that the phe- nolic compounds from coffee beans, tea leave and tubers can serve 0260-8774/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2009.04.022 * Corresponding author. Tel.: +66 74 286334; fax: +66 74 212889. E-mail address: soottawat.b@psu.ac.th (S. Benjakul). Journal of Food Engineering 95 (2009) 151–157 Contents lists available at ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng