Fabrication of bio-nanocomposite films based on fish gelatin reinforced with chitosan nanoparticles

Highlights

• CSNPs had spherical shape and size range about 40–80 nm.

• FG-based nanocomposite films were prepared using solution casting method.

• Incorporation of CSNPs improved the mechanical properties of the FG film.

• 6% (w/w) CSNPs loading decreased the WVP of the FG film by 50%.

Abstract

The paper focuses on the synthesis of chitosan nanoparticles (CSNPs) by ionic gelation between chitosan (CS) and sodium tripolyphosphate (TPP) and subsequently its use as filler in a fish gelatin (FG) matrix to produce bio-nanocomposite films. The obtained particles exhibited a spherical shape with size range of 40–80 nm, and a positively charged surface with a zeta potential value of +10 mV. XRD results confirmed the cross-linking reaction between CS and TPP. SEM images showed that CSNPs could be well dispersed in FG polymer matrix at low content, while higher CSNPs loadings (8%, w/w) resulted in the aggregation of particles in the composites. FTIR spectroscopy results confirmed the interaction between CSNPs and FG through hydrogen bonding. The nucleating effect of the CSNPs was confirmed by DSC analysis. Results indicated that the addition of CSNPs caused remarkable increase in the tensile strength (TS) and elastic modulus (EM), which leading to stronger films as compared with individual FG films, but decreased the elongation at break (EAB). Furthermore, addition of CSNPs contributed to the significant decrease (p < 0.05) of water vapor permeability (WVP), leading to a 50% decline at 6% (w/w) filler. The light barrier measurements presented low values of transparency at 600 nm of the FG-based nanocomposite films, indicating that these films are very transparent (lower in transparency value) while they have excellent barrier properties against UV light. The results presented in this study show the feasibility of using bio-nanocomposite technology to improve the properties of biopolymer films based on FG.

Introduction

Increasing and widespread environmental awareness, as well as efforts to reduce the volume flow of wastes and increase the use of renewable raw materials have placed emphasis on the disposal properties of different materials (Endres & Siebert-Raths, 2012). The non-degradable and non-renewable nature of plastic packaging has led to a renewed interest in packaging materials based on biopolymers derived from renewable sources. The use of biopolymer-based packaging materials can solve the waste disposal problem to a certain extent (Kumar, Sandeep, Alavi, Truong, & Gorga, 2010). The increscent interest in biopolymer based packaging has resulted in the development of protein-based films from soy protein, whey protein, casein, collagen, corn zein, gelatin, and wheat gluten (Cuq, Gontard, & Guilbert, 1998). Among all the protein sources, gelatin has also been extensively studied for its film forming capacity and applicability as an outer covering to protect food against drying, light and oxygen (Gómez-Guillén et al., 2009).

Fish gelatin (FG) has gained great interest in recent years as the demand for non-bovine and non-porcine gelatin has increased, due to religious and social reasons, and also the bovine spongiform encephalopathy (BSE) crisis (Bae et al., 2009). Furthermore, fish skin, which is a major byproduct of the fish-processing industry, causing waste and environmental pollution, could provide a valuable source of gelatin (Badii & Howell, 2006). The elaboration of edible films from fish gelatin has been recently studied (Gómez-Estaca et al., 2011, Hosseini et al., 2013, Núñez-Flores et al., 2012, Nur Hanani et al., 2012).

However, these biodegradable fish gelatin films do have some limitations in their use, such as low tensile strength (TS) and high water solubility (Gómez-Estaca et al., 2011). In order to improve the mechanical property as well as barrier characteristic of gelatin films, recently, a new class of materials namely bio-nanocomposites (biopolymer matrix reinforced with nanoparticles) has introduced as a promising option (Bae et al., 2009). Fillers with at least one nano-sized dimension (nanofillers or nanoreinforcements) have better interfacial adhesion with the polymer matrices, when compared to the respective micro/macroscopic reinforcements. A uniform dispersion of nanofillers leads to a very large matrix/filler interfacial area, changing the molecular mobility, improve the relaxation behavior, and the consequent thermal and mechanical properties of the resulting nanocomposite (Ludueña, Alvarez, & Vasquez, 2007). Nanocomposite technology using nanofillers such as carbon nanotubes (CNTs) (Ma, Yu, & Wang, 2008), nanoclay (Bae et al., 2009, Casariego et al., 2009), and nanosilica (Ahmed, Varshney, & Auras, 2010) has already proved to be an effective way to improve the mechanical, physical, and thermal properties of polymers. Newly, considering of the applications for edible films and/or food packing, much attention has been focused on polysaccharide nanofillers. Chitosan (CS) is a naturally occurring nontoxic, biocompatible, biodegradable, and cationic polysaccharide (Shahidi, Arachchi, & Jeon, 1999).

Chitosan nanoparticles (CSNPs) which are composed of a natural material with excellent physicochemical properties, is environmentally friendly, and bioactive (Yang, Wang, Huang, & Hon, 2010). CSNPs can be prepared by the electrostatic interaction and resultant ionotropic gelation between CS polycation and sodium tripolyphosphate (TPP) polyanion (Calvo et al., 1997, Yang et al., 2010). Using of these nanoparticles in edible films would be very promising, due to the food-grade properties of both components. De Moura et al. (2009) found that CS-TPP nanoparticles increases thermal and mechanical properties and decrease water vapor permeability of the hydroxypropyl methylcellulose (HPMC) films. In another study, these polysaccharide nanoparticles have been used as the reinforcing medium in glycerol plasticised-starch (GPS) matrices (Chang, Jian, Yu, & Ma, 2010). They have obtained an improvement of thermal stability, mechanical and barrier properties of GPS composites. More recently, Martelli, Barros, De Moura, Mattoso, and Assis (2013) was also reported that the incorporation of chitosan nanoparticles promoted noticeable improvement of the mechanical properties and acted in reducing the water vapor permeation rate in banana puree films.

Hence, bio-nanocomposite films based on FG and CSNPs could be a good candidate for food packaging applications to extent the shelf life of foods and products. This research focused on fabrication and characterization of CSNPs as well as evaluation of the effects of incorporation of obtained nanoparticles on morphology, mechanical properties, water vapor permeability, light barrier properties, and thermal behavior of FG films.