The effects of glycerol and guar-xanthan mixture on mechanical and barrier properties of starch based edible films Chemometric analysis

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1 The effects of glycerol and guar-xanthan mixture on mechanical and barrier properties of starch based edible films Chemometric analysis Danijela Z. Šuput 1, Vera L. Lazić 1, Lato L. Pezo 2, Senka Z. Popović 1, Nevena M. Hromiš 1, Sandra N. Bulut 1 1 Faculty of Technology, University of Novi Sad, Novi Sad, Serbia 2 Institute of General and Physical Chemistry, University of Belgrade, Belgrade, Serbia Abstract The aim of this work was to evaluate the simultaneous effect of glycerol (30, 40 and 50) and guar-xanthan gum addition (0.1, 0.3 and 0.5) effect on starch based edible film mechanical and barrier properties. According to Response Surface Methodology, the most influential parameter in the second order polynomial models calculation was the percentage of glycerol, while the linear term of guar-xanthan content was important only for second order polynomial model calculation for tensile strength and water vapor permeability. According to principal component analysis, samples grouping along the first component are primarily due to the content of glycerol, which is also confirmed by ANOVA analysis. According cluster analysis, two separate clusters are observed on the dendrogram, which includes the right (with the increased value of tensile strength) and the left cluster (with the increased value of elongation break and water vapor permeability). The observed distance of the two clusters is considerable (approx. 80). SCIENTIFIC PAPER UDC 664.2: :543:66 Hem. Ind. 70 (6) (2016) doi: /HEMIND S Keywords: edible films, plasticizers, characteristics, pattern recognition techniques. Available online at the Journal website: The structure of starch based edible films is rigid and fragile due to numerous interactions between polymer molecules, which have to be optimized so that film could be applied in food packaging industry. Wide range of plasticizers has been used for mechanical characteristics improvement [1,2]. Plasticizers weaken intermolecular interactions between polymer chains. New connections between starch molecules and plasticizer molecules occur instead of previous links between starch chains, which improves films flexibility [3 5]. As a consequence, the tensile strength value decreases, while elongation at break value increases. Starch is suitable matrix that can be used to obtain edible films with excellent barrier properties to oxygen and carbon dioxide. On the other hand, starch based edible films have poor barrier capacity against water vapor [6,7] due to their high hydrofilic nature [8]. Plasticizer addition affects, not only the mechanical properties, but also the barrier characteristics [9]. Plasticizer addition increases film hydrophilicity, which in turns increases water vapor permeability. Glycerol is plasticizer with the widest application due to its stability and compatibility with hydrophilic starch chains [10]. Hydroxyl groups of glycerol are responsible for inter- and intra-molecular interactions (hydrogen bonds) in the polymer chains, providing more flexible film structure [11]. Numerous studies have examined Correspondence: D.Z. Šuput, Faculty of Technology, University of Novi Sad, Bulevar Cara Lazara 1, Novi Sad, Serbia. suput.danijela@gmail.com Paper received: 19 August, 2015 Paper accepted: 5 February, 2016 polyol effect [5] and combined effect of plasticizers and surfactants on starch based edible films structure [12], as well as the influence of storage conditions on the characteristics of starch films [13,14]. In order to improve mechanical and barrier properties, it was also suggested to mix starch with other biopolymers [15,16]. Some authors [17,18] investigated xanthan effect on swelling, solubility and viscosity of whey and maze starch. It was proved that xanthan addition improves stability and viscosity of starch gels [19,20], as well as some mechanical characteristics, such as elongation at break [21]. Xanthan gum is an extracellular polysaccharide obtained by aerobic fermentation of Xanthomonas campestris. It has wide application in the food industry due to its ability to form viscous solutions at very low concentrations. Beside xanthan gum, wide application has also guar gum with similar characteristics. Guar gum acts as a thickening agent and stabilizer, helps maintaining structural homogeneity, functions as a binder. The aim of this work was to evaluate the simultaneous effect of glycerol and guar xanthan mixture addition on starch based edible films characteristics: mechanical (tensile strength and elongation at break) and barrier (water vapor permeability). Experimental results were subjected to analysis of variance (ANOVA) to show relations between applied assays. Response surface methodology (RSM) was used as an effective tool for optimizing of the process. Pattern recognition techniques (principal component analysis PCA and cluster analysis - CA) were applied on the experimental data (used as descriptors) to characterize and differ- 739

2 entiate among the observed samples. In further step, film with optimal glycerol and guar-xanthan content, regarding improved mechanical and barrier properties, will be applied as packaging for selected food products. MATERIAL AND METHODS Reagents Modified corn starch (C*EmTex 12688) and guar- -xanthan modified mixture (Lygomme KTC 58) were kindly provided by Palco (Kolbermoor, Germany). Glycerol (99.5) was obtained from Laboratorija (Novi Sad, Serbia). Film preparation Starch films were prepared by casting aqueous modified maize starch solution (1.5 mg/ml). Solution was heated at 90 C for 60 min in a water bath. Glycerol (30, 40 and 50) and guar-xanthan modified mixture (0.1, 0.3 and 0.5) were added in the film- -forming solution (Table 1). The film-forming solution was homogenized (10000 rpm for 1 min, Silent Crusher M, Heidolph, Germany) and then degassed under vacuum to remove dissolved air. Film-forming solution was cast into Petri dishes, previously covered with Teflon coating, and left to air dry on a leveled table surface at room temperature. Table 1. Experimental design Film sample Glycerol addition Guar-xanthan addition Mechanical properties Prior to the testing of mechanical properties, the films were conditioned for 48 h, at 25±0.5 C and 50±5 relative humidity. Films were visually examined and described. Tensile strength (TS) and elongation to break (EB) were measured on the Instron Universal Testing Instrument Model No 4301 (Instron Engineering Corp., Canton, MA), according to standard method ISO 527-3:1995 [22]. TS and EB measurements for each sample were repeated eight times. Water vapor barrier properties Moisture barrier properties of films were determined gravimetrically (dish method), according to the ISO 2528:1995 [23], condition A (temperature 25±1 C and relative humidity 90±2, obtained by saturated solution of potassium nitrate). The anhydrous silica gel was used as desiccant for filling the test dish. Test dishes were stored and weighed periodically until a constant rate of weight gain was reached. Obtained weighting values were used for calculation of the amount of moisture transferred through the film. Three replicates of each sample were tested simultaneously. Statistical analysis Collected data were subjected to ANOVA to explore the effects of process variables. Furthermore, pattern recognition techniques, including Principal Component Analysis (PCA) and Cluster Analysis (CA) were applied successfully to classify and discriminate the different samples. The evaluation of RSM, ANOVA, PCA and CA of the obtained results were performed using Statistica software, version 12 (StatSoft Inc. 2013, USA). RESULTS AND DISCUSSION Obtained results, related to mechanical and barrier properties of starch based edible films with different composition, in regard with glycerol and guar-xanthan amount additon, are presented in Table 2. Table 2. Mechanical and barrier properties of starch based edible films with different glycerol and guar-xanthan content 1 Film sample TS / MPa EB / WVP / g m 2 h Glycerol addition improved mechanical properties: TS values decreased, while EB values increased, which is in accordance with other authors findings [11,24,25]. On the other hand, glycerol addition negatively affected water vapor permeability (WVP), since this value increased. Glycerol is a hydrophilic molecule which decreases intermolecular attractions and increases molecular mobility [12] and it was expected that 740

3 water vapor permeability value increases. Guar-xanthan addition caused similar effects as glycerol addition. Mechanical properties were improved, while water vapor permeability was negatively affected [21]. These results were used for RSM calculations, which results are presented in Table 3. Table 3. Analysis of variance (ANOVA) for responces TS, EB and WVP; * significant at p < 0.05 level; 95 confidence limit, df degrees of freedom Material df TS MPa EB WVP 1 g m 2 h Glycerol * * * Glycerol * * 1.67 * Guar-xanthan * * 1.73 * Guar-xanthan Glycerol Guar-xanthan * 0.00 Error r The most influential parameter in the second order polynomial (SOP) model calculation, used for prediction of TS, EB and WVP, was the percentage of glycerol (the linear term was the most influential, p < 0.05). Linear term of guar-xanthan content was important only for SOP model calculation for TS and WVP. The quadratic term of guar-xanthan content was not statistically significant in any of the SOP models. Nonlinear interchange term of glycerol guar-xanthan was statistically significant only in the SOP model for EB calculation. Error in the Table 3, caused by the mismatch of the proposed model and the experimental data, indicated that developed models present the experimental results adequately. Also, high values of r 2 confirm the adequacy of the models. Table 4. The regression coefficients of the second order polynomial for response models of TS, EB and WVP; * significant at p < 0.05 level, ** significant at p < 0.10 level Coefficient TS MPa EB WVP 1 g m 2 h β ±10.25 * 15.16±1.93 * β ±0.44 ** 7.86±0.52 * 0.48±0.10 * β ±0.01 * 0.13±0.01 * 0.01±0.00 * β ±8.31 ** β 22 β ±0.20 * 0.01±0.04 ** Table 4 presents the regression coefficients of SOP models used for prediction of TS, EB and WVP. These coefficients can be used to calculate TS, EB and WVP, with desired content of glycerol and guar xanthan using developed SOP models. Figure 1 describes the response of TS, EB and WVP depending on the content of glycerol and guar xanthan. The picture shows the painted surfaces, which are the graphic representations of the developed mathematical models, while the white dots indicate the measured Figure 1. The dependence of TS, EB and WVP on glycerol and guar-xanthan content. 741

4 values for TS, EB and WVP. The highest value of TS is observed at a minimum concentration of glycerol and xanthan-guar, while the highest EB and WVP are recorded at maximum concentrations of glycerol and xanthan-guar, which is fully in agreement with the experimental data. Principal component analysis, as the orthogonal transformation, is applied in this work to display and group observed samples (according to TS, EB and WVP values) in the factor space. The points shown in the PCA graphics, which are geometrically close to each other, indicated the similarity of patterns that represent these points. The orientation of the vector describing the variable in factor space indicates an increasing trend of these variables, and the length of the vector is proportional to the square of the correlation values between the fitting value for the variable and the variable itself. The contribution of the variable TS, EB and WVP to calculate the factor of coordinates is shown in Table 3. The calculation of the first PC is almost equally affected by all variables, while TS most influence on the calculation of the second PC. Graphical representation of trends in the formation of edible films is shown in the first factor plane (described by PC 1 and 2), Figure 2a. It can be seen that the first two PC show of the total variability, which is considered sufficient to express the entire process Figure 2b shows the dendrogram for the CA analysis of the observed samples. The Complete linkage and City-block (Manhattan) algorithm distance were used for presentation of distances between points in 12-dimensional coordinate space. City-block (Manhattan) distances produced results similar to the Euclidean measurement, but is better suited for this research, due to the reduction of individual outliers impact, since it does not count the squares of the values of individual coordinates. The dendrogram in Figure 2b shows the analysis of the CA of the tested samples. Two separate clusters are observed on the dendrogram, which includes the right of samples 1-8 (with the increased value of TS) and the left cluster, which includes samples of 9-12 (with the increased value of EB and WVP). The observed distance the two clusters is considerable (approx. 80). CONCLUSION The samples containing less glycerol have shown higher TS values, while samples with increased glycerol content have shown higher EB and WVP values. ANOVA calculation of response parameters showed complex influence of linear and nonlinear terms of second order polynomial models and the parameters were influenced by all variables. Since the product quality was Figure 2. Pattern recognition techniques for starch based edible films: a) Biplot graph, b) Cluster analysis dendogram. variability. Samples on the right side of the graphics exerted higher TS values (glycerol content is lower), while samples located on the left side showed increased EB and WVP values. Grouping of samples along the first component (which covers of the total variance) is primarily due to the content of glycerol, which is also confirmed by ANOVA analysis. The position of samples regarding the second PC is determined by the content of guar xanthan. influenced by so many parameters and they were altered as the technological treatments change, PCA and CA were applied for evaluating the quality of product. Using the PCA and CA and revealing the coordinates of different trials, the position regarding product quality and directions for the improving of product characteristics can be realized. Glycerol content seems to be the most influential parameter for TS, EB and WVP values of edible films, which is confirmed by ANOVA and PCA analysis. 742

5 Acknowledgement This work is part of a project Osmotic dehydration of food energy and environmental aspects of sustainable production, project number TR-31055, financed by Ministry of Education, Science and Technological Development of the Republic of Serbia. REFERENCES [1] M. Ghasemlou, F. Khodaiyan, A. Oromiehie, M.S. Yarmand, Development and characterization of a new biodegradable edible film made from kefiran an exopolysaccharide obtained from kefir grains, Food Chem. 127 (2011) [2] D.F. Parra, C.C. Tadini, P. Ponce, A.B. Lugao, Mechanical properties and water vapor transmission in some blends of cassava starch edible films, Carbohydr. Polym. 58 (2004) [3] A. Jongjareonrak, S. Benjakul, W. Visessanguan, T. Prodpran, M. Tanaka, Characterization of edible films from skin gelatin of brownstripe red snapper and bigeye snapper, Food Hydrocoll. 20 (2006) [4] P.J.A. Sobral, J.S. Dos Santos, F.T. Garcia, Effect of protein and plasticizer concentrations in films forming solutions on physical properties of edible films based on muscle proteins of a Thai Tilapia, J. Food Eng. 70 (2005) [5] R.A. Talja, A. Helen, Y.H. Roos, K. Joupila, Effect of various polyols and polyol contents on physical and mechanical properties of potato starch-based films, Carbohydr. Polym. 67 (2007) [6] I. Arvanitoyannis, C.G. Billiaderis, Physical properties of polyol-plasticized edible films made from sodium caseinate and soluble starch blends, Food Chem. 62 (1998) [7] C. Pagella, G. Spigno, D.M. De Faveri, Characterization of starch based edible coatings. Food Bioprod. Process. 80 (2002) [8] V. Falguera, J.P. Quinterob, A. Jimenez, J.A. Munoz, A. Ibarz, Edible films and coatings: Structures, active functions and trends in their use, Trends Food Sci. Technol. 22 (2011) [9] R. Sothornvit, J.M. Krochta, Plasticizer Effect on Oxygen Permeability of β-lactoglobulin Films, J. Agric. Food Chem. 48 (2000) [10] M. Fernandez-Cervera, M. Karjalainen, S. Airaksinen, J. Rantanen, K. Krogars, J. Heinamaki, A. Iraizoz Colarte, J. Yliruusi, Physical stability and moisture sorption of aqueous chitosan amylose starch films plasticized with polyols, Eur. J. Pharm. Biopharm. 58 (2004) [11] A.C. Souza, G.E.O. Goto, J.A. Mainardi, A.C.V. Coelho, C.C. Tadini, Cassava starch composite films incorporated with cinnamon essential oil: Antimicrobial activity, microstructure, mechanical and barrier properties, Food Sci. Technol. 54 (2013) [12] M. Rodriguez, J. Oses, K. Ziani, J.I. Mate, Combined effect of plasticizers and surfactants on the physical properties of starch based edible films, Food Ress. Int. 39 (2006) [13] L. Fama, A.M. Rojas, S. Goyanes, L. Gerschenson, Mechanical properties of cassava starch edible films containing sorbates, Food Sci. Technol. 38 (2005) [14] S. Mali, M.V.E. Grossman, M.A. Garcia, M.N. Marrtino, N.E. Zaritzky, Effects of controlled storage on thermal, mechanical and barrier properties of plasticized films from different starch sources, J. Food Eng. 75 (2006) [15] C. Bangyekan, D. Aht-Ong, K. Srikulkit, Preparation and properties evaluation of chitosan coated cassava starch films, Carbohydr. Polym. 63 (2006) [16] Y. Xu, K. Kim, M. Hanna, D. Nag, Chitosan starch composite film: preparation and characterization, Ind. Crop. Prod. 21 (2005) [17] F. Wang, Z. Sun, Y.J. Wang, Study of xanthan gum/waxy corn starch interaction in solution by viscometry, Food Hydrocolloids 15 (2001) [18] I.G. Mandala, E. Bayas, Xanthan effect on swelling, solubility and viscosity of wheat starch dispersions, Food Hydrocolloid. 18 (2004) [19] N.A. Abdulmola, M.W.M. Hember, R.K. Richardson, E.R. Morris, Effect of xanthan gum on the small-deformation rheology of crosslinked and uncrosslinked waxy maize starch, Carbohydr. Polym. 31 (1996) [20] V. Sudhakar, R.S. Singhal, P.R. Kulkar, Starch gum interactions: Nutritional and technological implications, Int. J. Food Sci. Nutr. 47 (1996) [21] P. Veiga-Santos, L.M. Oliveira, M.P. Cereda, A.J. Alves, A.R.P. Scamparini, Mechanical properties, hydrophilicity and water activity of starch gum films: Effect of additives and deacetylated xanthan gum, Food Hydrocolloid. 19 (2005) [22] ISO 527 3:1995: Plastics Determination of tensile properties Part 3: Test conditions for films and sheets, International Organization for Standardization, Geneva, [23] ISO 2528:1995: Sheet materials determination of water vapour transmission rate Gravimetric (dish) method, International Organization for Standardization, Geneva, [24] M. Ghasemlou, N. Aliheidari, R. Fahmi, S. Shojaee- -Alibadi, B. Keshavarz, M.J. Cran, R. Khaksar, Physical, mechanical and barrier properties of corn starch films incorporated with plant essential oils, Carbohydr. Polym. 98 (2013) [25] S. Benavides, R. Villalobos-Carvajal, J.E. Reyes, Physical, mechanical and antibacterial properties of alginate film: effect of the crosslinking degree and oregano essential oil concentration, J. Food Eng. 110 (2012)

6 IZVOD UTICAJ GLICEROLA I SMEŠE GUAR-KSANTANA NA MEHANIČKA I BARIJERNA SVOJSTVA JESTIVIH FILMOVA OD SKROBA HEMOMETRIJSKA ANALIZA Danijela Z. Šuput 1, Vera L. Lazić 1, Lato L. Pezo 2, Senka Z. Popović 1, Nevena M. Hromiš 1, Sandra N. Bulut 1 Tehnološki fakultet, Univerzitet u Novom Sadu, Bulevar Cara Lazara 1, Novi Sad, Srbija 2 Institut za opštu i fizičku hemiju, Univerzitet u Beogradu, Studentski Trg 12, Beograd, Srbija (Naučni rad) Ispitivanje funkcionalnih karakteristika jestivih hidrokoloida sa ciljem unapređenja svojstava predstvalja značajan izazov. U radu je ispitan uticaj dodatka plastifikatora glicerola i smeše guar-ksantana na mehaničke (zatezna jačina i izduženje pri kidanju) i barijerne karakteristike (propustljivost vodene pare) jestivih skrobnih filmova. Jestivi skrobni filmovi su izuzetno aplikativni u prehrambenoj industriji zbog niza prednosti: niska cena, ekološka podobnost, inertnost prema upakovanom sadržaju. Ipak, njihovu primenu najviše ograničva krta priroda filma i visoka propustljivost vodene pare, koja je posledica hidrofilne prirode skroba. Dodatak glicerola ima zadatak da redukuje intermolekularne sile i poveća mobilnost biopolimernih lanaca čime se povećava fleksibilnost filmova. Dokazano je da ksantan pozitivno utiče na ponašanje skroba u smislu poboljšanja stabilnosti, viskoziteta filmova, stepena rastvorljivosti i bubrenja. Guar guma, takođe, ima funkciju zgušnjivača i stabilizatora, pomaže održavanju homogenosti i strukture, funkcioniše kao vezujuće sredstvo. Obzirom da su obe komponente kompatibilne sa skrobom i odobrene za primenu u prehrambenoj industriji u postupku proizvodnje jestivih filmova aplicirali smo i smešu guar-ksantana, kako bi se ispitao uticaj na osobine dobijenih filmova. Potvrđeno je da dodatak glicerola unapređuje mehaničke osobine filmova. Vrednost zatezne jačine se smanjuje dok vredost izduženja pri kidanju raste. U okviru svake grupe uzoraka, dodatkom smeše guar-ksantana vrednosti zatezne jačine se dodatno smanjuju, a vrednosti izduženja pri kidanju rastu. Sa druge strane, prisustvo glicerola povećava transmisiju vodene pare, bez obzira na formulaciju filma, što za posledicu ima značajno veće vrednosti propustljivosti vodene pare filmova kojima je dodat plastifikator nego kod filmova bez plastifikatora. Uticaj dodatka guar-ksantana izaziva promene propustljivosti vodene pare, ali je slabije izražen na ovu osobinu filmova. Metodom odzivnih površina je određen simultani efekat dodatka glicerola i dodatka smeše guar-ksantana na mehaničke i barijerne osobine jestivih skrobnih filmova. Ustanovljeno je da je najuticajniji parametar u modelu (u obliku polinoma drugog reda) procenat glicerola, dok je linearni član sadržaja guar ksantana bio statistički značajan samo u modelu za predikciju zatezne čvrstoće i propustljivosti vodene pare. Na osnovu analize glavnih komponenata (PCA), izvršeno je grupisanje uzoraka u faktorskoj ravni i ustanovljeno je da sadržaj glicerola utiče prvenstveno na raspoređivanje tačaka po prvoj glavnoj komponenti, što je potvrđeno ANOVA analizom. Na osnovu klasterske analize (CA), formirana su dva razdvojena klastera na dendogramu, jedan koji se nalazi na desnoj strani (uzorci sa povećanom vrednošću zatezne jačine), i levi klaster koji obuhvata uzorke koji imaju povećane vrednosti izduženja pri kidanju i propustljivosti vodene pare. Uočena udaljenost između dva klastera je bila značajno izražena (oko 80). Ključne reči: Jestivi filmovi Plastifikatori Karakteristike Tehnika prepoznavanja strukture 744