CASHEW GUM AND GELATIN BLEND FOR FOOD PACKAGING APPLICATION

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1 CASHEW GUM AND GELATIN BLEND FOR FOOD PACKAGING APPLICATION M.A.Oliveira 1, R.F. Furtado 1, M.S.R. Bastos 1, S.D. Benevides 1, C.R. Muniz 1, A. Biswas 2, H.N. Cheng 3 1 Laboratory of food packaging Embrapa Tropical Agroindustry CEP: 6111 Fortaleza CE Brazil, (a) Telephone: + (8) (marilia.oliveira@pq.cnpq.br; roselayne.furtado@embrapa.br; socorro.bastos@embrapa.br; selene.benevides@embrapa.br; celli.muniz@embrapa.br) 2 USDA Agricultural Research Service, National Center for Agricultural Utilization Research, 181 North University Street, Peoria, IL 6164, USA, Telephone: (39) (Atanu.Biswas@ars.usda.gov) 3 USDA Agricultural Research Service, Southern Regional Research Center, 11 Robert E. Lee Blvd., New Orleans, LA 7124, USA, Telephone: (4) (HN.Chen@ars.usda.gov) ABSTRACT Cashew gum (CG) and gelatin (G) films were developed using the casting method and response surface methodology. The objective was produce packaging films from CG/G blends that exhibit effective barrier properties. A study of zeta potential versus ph was first carried out to determine the isoelectric point of the 1:1 CG/G solution. The films with different CG/G ratios were then examined for permeability to water vapor (WVP), thickness, solubility, mechanical properties and surface morphology (via scanning electron microscopy, SEM). The blend films were shown to have better properties than the film from each polymer separately. The best result was obtained for the film blend with :2. CG/G (w/w). KEYWORDS: Cashew gum; gelatin; biodegradable, ecofriendly, alternative packaging. 1. INTRODUCTION Polymer blending is a well-known process to develop new materials and to vary polymer properties. A main advantage of this approach is to obtain high performance materials without investing in new synthetic routes. In optimal cases, mixtures of polymers result in materials with better properties than the pure components. It is also known that the use of biopolymers has the benefit of being eco-friendly and sustainable. Thus, biopolymers are often used as biodegradable packaging films; examples include cellulose and starch derivatives, alginate, pectin, chitosan, and certain gums (Tharanathan, 23). The cashew tree (Anacardium occidentale L.) is a native plant from northeastern Brazil that exudes a gum in response to attack by pathogens and injuries. This gum is composed of a branched heteropolysaccharide with a complex structure involving galactose, arabinose, rhamnose, glucose and glucuronic acid. This material is soluble in water and can be made into a film with the addition of a suitable plasticizer such as glycerol and sorbitol. Plasticisers reduce interactions between adjacent molecules and increase the flexibility of the film (Aider, 21). However, even with the use of glycerol at high concentrations, CG films are brittle and inflexible, making necessary the incorporation of a protein or other polymeric materials to improve the mechanical properties. We have found gelatin to be a good blending partner for CG. Both G and CG are available, biodegradable and biocompatible, and are good starting materials for product development. Earlier papers reported that gelatin can contribute to improved physical and chemical properties of polysaccharides films. Thus, Mamani (29) noted that the composite films from methylcellulose, glucomannan, pectin, and gelatin showed good

2 mechanical properties and oxygen permeability. Pectin films properties were improved due to the addition of gelatin and/or soy flour protein (Liu et al., 27). The aim of this study was to develop and characterize films of CG / G blends, particularly with respect to their barrier and mechanical properties, for possible use in food packaging. 2. MATERIALS AND METHODS 2.1 Materials Cashew gum was collected from Embrapa Experimental Station at Pacajus (Fortaleza-Ceará). It was ground to 1-mesh particle size, and the resulting powder was solubilized in water at the ratio of 1:3 (w/v) for 4 hours, centrifuged at 1, rpm at 4 C for 2 minutes, and filtered to remove the insoluble materials. Ethanol in the ratio of 1:4 (v/v) was added to the solution for 24 h to precipitate the cashew gum. The precipitate was filtered, washed with acetone, and dried in a hot air circulation oven. Gelatin 22H B type (ph =.4) was kindly supplied by Rousselot (São Paulo, Brazil). 2.2 Film Formulation Eleven films were formulated according to a central composite design (CCD) based on the response surface methodology. The study consisted of 11 randomized runs (Table 1) with two independent variables CG and G, both in the range from 2. to 7. g. Water was used as the solvent with 1% w/w glycerol in all runs. In our procedure, gelatin and glycerol were stirred in 1 ml water overnight at C. Cashew gum was added and homogenized using an Ultra Turrax homogenizer (model T2, IKA, Wilmington, NC, USA) at 1, rpm for 1 minutes. The films were subsequently prepared by the casting method. Table 1. Coded values and uncoded values (real experimental values) of the independent variables according to the central composite design. Treatments Coded Uncoded CG G CG (g) G (g) Film Characterization Dried film samples were cut and detached from the surface. Before the characterization of the films, the samples were conditioned in desiccators. The following analyses were conducted. Zeta potential analysis: The measurement of zeta potential was performed as a function of ph change, using a Malvern Zeta Meter (Malvern, UK). The tests were made using CG/G 1/1 (w/w) in distilled water. The reagents used for varying the ph were HCl (.1 mol/l) and NaOH (.1 mol/l).

3 Thickness determination: This was carried out with a digital micrometer (Digimatic model, Mitutoyo, Brazil) with a range of -2 mm and an accuracy of ±.1 mm. The thickness used was the arithmetic average of eight measurements made randomly along each sample evaluated. WVP analysis: This was determined according to Method E96-8 (ASTM, 2). Eight replicate samples (6-mm diameter each) were placed between the acrylic permeation cell fittings with a circular opening (φ = mm), corresponding to the film area exposed to migration. Each cell contained in its interior ml of distilled water. The cells were placed in a desiccator (2 ± C and 3 ± % relative humidity) containing silica gel. The weight of the cells was observed each hour on an analytical balance for 24 h. Solubility: The water solubility determination was carried out on 3 cm x 3 cm film pieces based on the method proposed by Gontard et al. (1994), with some modifications. Previously dried and weighed samples were immersed in ml of distilled water for 24 h at 2 ºC with stirring (7 rpm). The dry weight of the remaining film pieces was obtained after filtration on previously dried and weighed filter paper and used to calculate the insoluble matter as a percentage of the initial dry weight (g/1 g). All the dry weights (of the initial and final film pieces and the filter paper) were determined after drying at 1ºC for 24 h using a fan-assisted convection oven (Quimis model Q 31 4M22, Brazil). SEM analysis: Morphological characterization was performed by SEM (Zeiss DSM, model 94A). Samples were sputter coated with thick platinum layers using an evaporator (Electron Microscopy Sciences, Hatfield, PA, USA) and examined on the SEM using an accelerating voltage of 1 kv and a magnification of 1X. Mechanical testing: This was conducted according to Method D882-9 (ASTM, 29) on a mechanical tester (EMIC DL 3) on 12.8-cm strip film samples. The initial grip separation and cross-head speed were set to 1 cm/min. Both force (N) and deformation (mm) were recorded during extension. Tensile strength was calculated by dividing the required force for film rupture by the crosssectional area, and elongation at break was calculated as the percentage increase in sample length. The elastic modulus was calculated from the slope of the stress strain curve in the elastic deformation region. The reported values are the averages of five measurements. 3. RESULTS AND DISCUSSION A filmogenic solution of CG/G 1:1 (m/m) was tested for zeta potential in the ph range from 2 to 9 as shown in Figure 1 Figure 1. Zeta Potential of filmogenic solution CG/G (1:1 w/w) versus ph. Values of ph between 4 and 2. showed the presence of positively charged species because of the protonation of G (NH 2 ) and CG (OH). At ph 6-9, the zeta potential was reduced from -3.9 to -.3

4 mv due to the anionic nature of cashew gum (pka=4.) and the ionization of amino acid residues of gelatin (isoelectric point being ) (Ward, 197; Nikitina et al., 211). Thus, all further studies were done at ph in order to avoid repulsion charges between molecules. The films obtained in this work were found to have thicknesses that varied randomly from 3 to 1 mm, and no correlation was observed with the composition of the blend. The same finding was observed by Wang et al. (211) who saw no correlation in the film thickness with carboxymethyl cellulose composition. Figure 2a shows the response surface plot for solubility; it can be seen that at higher concentrations of CG there was a decreasing trend in solubility. It may be noted that at ca. : CG/G (viz., treatments 4 and 9) the solubility decreased, reaching minimum values at 4 and 47% respectively. Films with low solubility in water are desirable in order to avoid disintegration of packaging in excessively humid conditions. The water-solubility values found in this study were lower than those reported by Yamashita et al. (2) in biodegradable films of starch-based cassava containing calcium propionate and potassium permanganate as preservatives, where solubility values ranged from 78 to 86 %. Figure 2b shows the response surface for WVP analysis. The proportion around : GC/G shows the best water vapor barrier properties represented by treatments 1-4 and 7 (1 to 2 g.mm.k.pa - 1.h.m -2 ). In contrast, films from the biopolymers alone have high permeability to water vapor (> 3 g.mm.k.pa.h.m -2 ), making them less suitable for applications requiring a good water vapor barrier (Azeredo et al. 216; Wu et al., 216). Figure 2. Tridimensional response surface plot of solubility and permeability to water vapor (WVP) analysis. Scanning electron photomicrographs of CG/G blends are shown in Figure 3. It is observed that for treatments where G is prevalent, the surface is more irregular. Thus, treatment 8 (CG=.g and G= 7.g) has a more irregular surface than treatment 7 (CG=.g and G= 2.g). Figure 3. SEM photomicrographs of the CG / G blends for: (A) surface and (B) cross section of treatment 8 (CG=.g and G= 7.g); (C) surface and (D) cross section of treatment 7 (CG=.g and G= 2.g). The analysis conditions entailed 1. kv, magnification 1x, and 2 µm range.

5 Films prepared with only the polysaccharide showed no mechanical strength, making the addition of gelatin necessary. For gelatin film, the elastic modulus was 42, MPa, tensile strength 3 MPa and elongation at break.86 %. The GC/G blends had Young's modulus values (Figure 4a) that were similar to gelatin film (around 3,-4, MPa) with the exception of treatments 7 and. The tensile strength values (Figure 4b) showed large variations, reaching a maximum of 8 MPa for treatment 8 (:, GC/G). Figure 4. Tridimensional response surface plots as a function of cashew gum and gelatin mass for (a) Young's modulus (MPA), (b) tensile strength (MPa), and (c) elongation at break (%). (a) (d) (c) For elongation at break (Figure 4c), treatments and 7 gave the best results with to 11% (around 1 times more elongation than gelatin). Thus, films corresponding to treatments and 7 were ductile and underwent plastic deformations before their fracture. The mechanical characteristics of CG/G films were superior to films reported in the literature using other polysaccharides (Costa et al., 21; Nur Haziraha, Isab and Sarbon, 216). It is well known that variations in film composition, either in the biopolymer or the plasticizer, influence the mechanical properties of the films directly. Cerqueira et al. (212) showed earlier that increased glycerol concentration resulted in higher elongation at break. For this reason, glycerol was chosen as the plasticizer in this work. 4. CONCLUSION Cashew gum and gelatin blends form films with improved mechanical strength compared to the individual components. The blend in treatment 7 (CG=.g and G= 2.g) is especially appropriate for packaging application in view of its mechanical and barrier properties.

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