Effects of Concentration of ZnO Nanoparticles on Mechanical, Optical, Thermal, and Antimicrobial Properties of Gelatin/ZnO Nanocomposite Films

Transcription

1 KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY Vol. 20, No. 2 41~49 (2014) Effects of Concentrtion of ZnO Nnoprticles on Mechnicl, Opticl, Therml, nd Antimicrobil Properties of Geltin/ZnO Nnocomposite Films Shiv Shnkr, Xinnn Teng, nd Jong-Whn Rhim* Deprtment of Food Engineering nd Bionnocomposite Reserch Institute, Mokpo Ntionl University, Mun , Kore Abstrct This study illustrtes the synthesis of geltin bsed zinc oxide nnoprticle (ZnONPs) incorported nnocomposite films using different concentrtions of ZnONPs. The ZnONPs were ovl in shpe nd the size rnged from nm. The nnocomposite films were chrcterized by UV-visible, FE-SEM, FT-IR, nd XRD. The concentrtions of ZnONPs gretly influenced the properties of nnocomposite films. The bsorption peks round 360 nm incresed with the incresing concentrtions of ZnONPs. The surfce color of film did not chnge while trnsmittnce t 280 nm ws gretly reduced with increse in the concentrtion of ZnONPs. FTIR spectr showed the interction of ZnONPs with geltin. XRD dt demonstrted the crystlline nture of ZnONPs. The thermostbility, chr content, wter contct ngle, wter vpor permebility, moisture content, nd elongtion t brek of nnocomposite films incresed, wheres, tensile strength nd modulus decresed with increse in the concentrtions of ZnONPs. The geltin/znonps nnocomposite films showed profound ntibcteril ctivity ginst both Grm-positive nd Grm-negtive food-borne pthogenic bcteri. The geltin/znonp 1.5 nnocomposite film showed the best UV brrier nd ntimicrobil properties mong the testedfilms, which indicted high potentil for use s n ctive food pckging films with environmentlly-friendly nture. Keywords Geltin, ZnO nnoprticles, Nnocomposite film, UV brrier, Antibcteril ctivity Introduction In the present decde, there hs been tremendous ttention on the development of ntimicrobil food pckging films for controlling the microbiologicl decy of perishble food products 1). The min components of food stuffs re wter, crbohydrtes, proteins, fts nd minerl slts which provide the pproprite conditions for microbil growth under mbient temperture 2). The ntimicrobil food pckging films hve shown gret potentil to inhibit the growth of both Grm-positive nd Grm-negtive food-borne pthogens 1). These films re usully prepred by incorporting ntimicrobil gents which ct upon food-borne microorgnisms nd inhibit their growth. Vrious types of orgnic nd inorgnic mterils hve been used to prepre ntimicrobil pckging mterils 3,4). Among metllic nnoprticles, silver, copper, nd zinc nnoprticles hve proven strong ntimicrobil ctivity ginst Corresponding Author : Jong-Whn Rhim Deprtment of Food Engineering nd Bionmocomposite Reserch Institute, Mokpo Ntionl University, Mun , Kore Tel: , Fx: E-mil : jwrhim@mokpo.c.kr Grm-positive nd Grm-negtive bcteri 5,6). The current reserch work focuses on the use of zinc oxide nnoprticles (ZnONPs) s ntibcteril gents to prevent bcteril growth becuse of their low cost s compred to other metllic nnoprticles. Moreover, ZnONPs possess high ultrviolet bsorption property which mkes it suitble for the use s UV-screening film. In ddition, ZnONPs re believed to be nontoxic nd listed s generlly recognized s sfe GRAS substnces by FDA 7). Recently, there hve been severl reports regrding the ntimicrobil ctivity of ZnO nnoprticles 4). The present study ws imed to prepre ZnONPs incorported geltin nnocomposite film with improved UV brrier nd ntimicrobil properties, which could be used s n ctive food pckging mterils. In ddition, the influence of different concentrtions of ZnONPs on the morphology, crystlliztion behvior, therml, mechnicl, brrier, nd ntibcteril properties of the geltin bsed nnocomposites were investigted. Experimentl Mterils Geltin ws purchsed from Gel Tec Co., Ltd. (Seoul,

2 42 Shiv Shnkr et l. Kore Journl of Pckging Science & Technology Kore). Sodium crboxymethyl cellulose (CMC) nd zinc cette dehydrte were procured from Junsei Chemicl Co., Ltd (Tokyo, Jpn). Sodium hydroxide nd glycerol were obtined from Smchun Pure Chemicl Co., Ltd. (Pyeongtek, Yeonggi-do, Kore) nd Dejung Chemicls & Metls Co., Ltd. (Siheung, Gyonggido, Kore), respectively. Tryptic soy broth (TSB), brin hert infusion broth (BHI) nd gr powder were bought from Duksn Pure Chemicls Co., Ltd (Ansn, Gyeonggi-do, Kore). All the regents were of nlyticl grde nd used without further purifiction. Preprtion of ZnO nnoprticle Zinc oxide nnoprticles (ZnONPs) were prepred using zinc cette s source of zinc nd sodium hydroxide s reducing gent in the presence of cpping gent (CMC) 8). For the preprtion of ZnONPs, 0.15 g CMC ws dissolved in 150 ml distilled wter by heting the solution t 90 o C for bout 10 min with constnt stirring. The mixture ws cooled to 80 o C. Ech zinc cette of , 1.5, nd 2.5 mm ws then dded nd stirred continuously until they dissolved completely. Therefter, 1, 2, 3 nd 5 ml of 1 M sodium hydroxide solution ws dded drop-wise in 0.5, 1.0, 1.5, nd 2.5 mm zinc cette solution, respectively nd continued stirring t 80 o C for 20 min. The formtion of milky white solution indicted the formtion of ZnONPs. The ZnONPs formed with different concentrtions of zinc cette were designted s ZnONP 0.5, ZnONP 1.0, ZnONP 1.5, nd ZnONP 2.5, respectively. Preprtion of geltin/zno nnoprticle nnocomposite film Geltin nd geltin/zno nnoprticle nnocomposite films were prepred by the solution csting method s described by Rhim et l. 9). 4 g of geltin ws dded slowly in 150 ml of the bove prepred ZnONPs solutions with stirring until they dissolved completely, followed by the ddition of 1.2 g glycerol s plsticizer nd continued stirring t 80 o C for 20 min using mgnetic stirrer with thermostt (with controlled temperture). The film forming solution ws csted evenly on leveled Teflon film (Cole-Prmer Instrument Co., Chicgo, IL, USA) coted glss plte (24 30 cm) nd dried t room temperture for bout 48 h. The completely dried films were peeled off from glss pltes nd preconditioned t 25 o C nd 50% RH for 48 h before further chrcteriztions. The control geltin nd geltin/cmc films were prepred by the sme method without ddition of ZnONPs. The geltin/znonps nnocomposite films were nmed s geltin/znoa CMC0.5, geltin/znoa CMC1.0, geltin/znoa CMC1.5, nd geltin/znoa CMC2.5. Chrcteriztion of geltin/znonps nnocomposite films Morphologicl observtion, FT-IR nd XRD nlysis For the field emission scnning electron microscopic (FE- SEM) nlysis, the smll piece of film ws mounted on SEM specimen holder nd nlyzed using FE-SEM (S-4800, Hitchi Co., Ltd., Mtsud, Jpn) with n ccelerting voltge of 5.0 kv. Fourier trnsform infrred (FT-IR) spectr of the films were obtined using n ttenuted totl reflectnce-fourier trnsform infrred (AT-FTIR) spectrophotometer (TENSOR 37 spectrophotometer with OPUS 6.0 softwre, Billeric, MA, USA) t resolution of 4 cm -1. For X-ry diffrction (XRD) pttern of the films ws nlyzed by X-ry diffrctometer (PANlyticl Xpert pro MRD diffrctometer, Amsterdm, Netherlnds). The spectr were recorded using Cu Ká rdition (wvelength of nm) nd nickel monochromtor filtering wve t 40 kv nd 30 ma. Surfce color nd opticl properties The surfce color of the films ws mesured by Chrom meter (Konic Minolt, CR-400, Tokyo, Jpn) with white color plte (L=97.75, =-0.49, nd b=1.96) s stndrd bckground. Hunter color vlues (L,, nd b) were determined by tking n verge of five redings from ech film smple. Totl color difference (E) ws clculted s follows: E = [( L) 2 + ( ) 2 + ( b) 2 ] 0.5 where L,, nd b re the difference between ech color vlue of stndrd color plte nd film smples, respectively. For opticl properties of the films, ech film smple ws directly mounted between two spectrophotometer mgnetic cells. The bsorbnce nd percent trnsmittnce spectr were mesured using UV-vis spectrophotometer (Mecsys Optizen POP Series UV/Vis, Seoul, Kore). Absorbnce ws tken in the wvelength of 200~700 nm t 1 nm intervl. Trnsprency of the films ws tested by mesuring percent trnsmittnce t 280 nm (T 280 nm) nd 660 nm (T 660 nm). Wter vpor permebility, wter contct ngle nd moisture content The wter vpor permebility (WVP) of the films ws determined grvimetriclly ccording to the stndrd method of ASTM E96-95 with slight modifiction 10). The films were cut into squre pieces (7.5 cm 7.5 cm) nd directly mounted horizontlly on the top of WVP mesuring cups contining 18 ml of wter. The cups were weighted nd subsequently plced in n environmentl chmber controlled t 25 o C nd 50% RH with ir movement t 198 m/min. The weight of the cups ws tken ech 60 min period during 8 h. Wter vpor trnsmission rte (WVTR) ws clculted from the slopes (liner) of the stedy stte portion of weight loss of the cup versus time curve. Then, the WVP of the films ws clculted in g.m/m 2.s. P s follows:

3 Vol. 20, No. 2 (2014) Geltin/ZnO Nnocomposite films 43 WVP = (WVTR L) / p where WVTR ws the mesured wter vpor trnsmission rte (g/m 2.s) through film, L ws the men thickness of the film (m), nd p ws prtil wter vpor pressure difference (P) cross the film. The wter contct ngle (WCA) of the film ws mnesured by WCA nlyzer (model Phoenix 150, Surfce Electro Optics Co., Ltd., Kunpo, Kore). Ech film ws cut into rectngulr pieces (3 cm 10 cm) nd plced on the horizontl stge (Blck Teflon coted steel, 7 cm 11 cm). The drop of wter (~10 µl) ws plced on the surfce of the film. The contct ngle ws mesured on both sides of the wter drop to ssume symmetry nd horizontl level 11). The verge vlues of three mesurements of ech smple were presented s the degree of WCA. For moisture content (MC) nlysis, ech film ws cut into 3cm 3 cm nd dried t 100 o C for 24 h using hot ir oven 12). The weight loss of ech film ws mesured s MC nd expressed s percent MC bsed on the initil weight of the film. Thickness nd tensile properties of the films Thickness of the film smples ws mesured by hndheld micrometer (Dil Thickness Guge 7301, Mitutoyo Corportion, Kngw, Jpn). The verge vlues of five rndom mesurements were tken for ech film thickness. The tensile strength (TS), elongtion t brek (E), nd elstic modulus (EM) of ech film were mesured ccording to the stndrd test method of ASTM D using Instron Universl Testing Mchine (Model 5565, Instron Engineering Corportion, Cnton, MA, USA). Ech film ws cut into rectngulr strips (2.54 cm 15 cm) nd tensile properties were mesured with n initil grip seprtion of 50 mm nd crosshed speed of 50 mm/min. The TS ws expressed s MP, nd determined by dividing the mximum lod (N) by the initil cross-sectionl re (m 2 ) of the films. The E ws expressed s %. It ws determined by dividing the extension t the rupture of the film by the initil length of the film (50 mm) multiplied by 100. The modulus (MP) ws determined from the slope of the liner portion of the stress strin curve, which corresponds to the stress divided by the strin of the film smple. Ten mesurements were crried out for ech film nd the verge vlues were presented. Therml stbility Therml stbility of the films ws determined using thermogrvimetric nlyzer (TGA, Hi-Res TGA 2950, TA Instrument, New Cstle, DE, USA). About 5 mg of ech film smple ws tken in stndrd luminum cup nd heted in the temperture rnged from 30~600 o C with heting rte of 10 o C/ min under nitrogen flow of 50 cm 3 /min. Empty cup ws tken s reference. The derivtive of TGA (DTG) ws obtined by clculting differentils of TGA vlues using centrl finite difference method s follows [9]: DTG = (W t+ t W t- t ) / 2 t where, W t+ t W t - t re the residul weight of smple t time t+ t nd t t, respectively, nd t is the time intervl for reding residul smple weight 13). Antimicrobil ctivity The ntibcteril ctivities of net gr nd gr/cunps BNC films were exmined s their inhibitory effects ginst the growth of Grm-positive bcteri, L. monocytogenes nd Grm-negtive bcteri, Escherichi coli. Both bcteri were supplied by the Koren culture collection center (Seoul, Kore). L. monocytogenes nd E. coli were septiclly inoculted in 20 ml TSB nd BHI broth, respectively nd subsequently incubted t 37 o C for 16 h. Ech cultured broth ws centrifuged t 5000 rpm for 10 min. The cell pellets were suspended in 100 ml of sterile TSB nd BHI broth respectively, nd diluted 10 times with sterile distilled wter. 50 ml of diluted broth (~10 6 CFU ml -1 ) ws tken into 100 ml of the conicl flsk contining film smple (5 cm 5 cm) nd subsequently incubted t 37 o C for 12 h under mild shking. The sme diluted broth without film smple ws used s the control. At every three hour intervl, the cell vibility of ech pthogen ws clculted by counting bcteril colonies on the pltes. Antimicrobil tests were performed in triplicte with individully prepred films. Sttisticl nlysis Sttisticl nlysis ws done by one wy nlysis of vrince (ANOVA). The significnce of ech men vlue ws determined (p<0.05) with the Duncn s multiple rnge tests using the SPSS softwre (SPSS Inc., Chicgo, IL, USA). Results nd Discussion Morphology nd EDS nlysis The chnged ppernce of solution from trnsprent to milky white with time indicted the formtion of ZnO nnoprticles. The morphology of ZnONPs, net geltin film, nd geltin/znonps nnocomposite films is presented in Fig. 1. The nnoprticles were in the form of colloidl solution nd nm in size. The net geltin film hd smooth nd compct surfce, while geltin/znonps nnocomposite films showed rough surfces. The zinc nnoprticles were uniformly distributed throughout the films without ny ggregtion of prticles. Similr surfce morphology of nnocomposite films ws observed by Knmni nd Rhim, who prepred nnocomposite films by blending ZnO nnoprticles

4 44 Shiv Shnkr et l. Kore Journl of Pckging Science & Technology Fig. 1. FE-SEM imges of () ZnONPs (b) net geltin nd (c) geltin/znonpcmc2.5 nnocomposite films. Fig. 2. EDS nlysis of () net geltin, (b) geltin/znonpcmc0.5, (c) geltin/znonpcmc1.0, geltin/znonpcmc1.5, nd geltin/znonpcmc2.5 nnocomposite films. with different polymer mtrices8). Fig. 2 shows the electron dispersive spectroscopy (EDS) nlysis of nnocomposite films. The percentge of Zn incresed with the incresing concentrtions of ZnONPs in the nnocomposite films. Opticl nd color properties The opticl properties of geltin nd geltin/znonps nnocomposite films re shown in Fig. 3. The net geltin film showed two peks round nm nd nm for chrcteristic peks of geltin. However, the nnocomposite films blended with ZnONPs showed n dditionl pek ner 360 nm for chrcteristic pek of ZnONPs. The pek intensity ws incresed when the concentrtion of ZnONPs incresed from 0.5 to 2.5 M. Kim et l.14) lso reported the similr results for bsorption pek of ZnONPs t round nm nd the pek intensity incresed with the increse in concentrtion of ZnONPs from 1% to 10%. The light trnsmittnce t 660 nm nd 280 nm of nnocomposite films ws mesured nd presented in Tble 1. Trns- Fig. 3. UV-visible spectr of geltin/znonps nnocomposite films. mittnce vlues of the net geltin film t 660 nm nd 280 nm

5 Vol. 20, No. 2 (2014) Geltin/ZnO Nnocomposite films 45 Tble 1. Opticl properties of geltin/znonps nnocomposite films Film L c T280nm (%) E b d T660nm (%) 1.82±0.09 e 28.9± ±0.7c Geltin 93.30±0.09 Geltin/CMC 93.24±0.15c -0.54±0.03d 4.40± ± ±1.0d 90.0±0.6c Geltin/ZnONP ±0.06b ±0.03c 5.52±0.10b 3.10±0.11b 13.0±1.8c 90.1±0.5c Geltin/ZnONP ± ±0.05b 6.72±0.14c 4.38±0.14c 1.9±0.1b 88.9±1.2c 1.5 d d 77.1±5.6b Geltin/ZnONP 92.73± ± ± ± ± ± ±0.1 Geltin/ZnONP ±0.12b -1.98± ±0.32d 5.61±0.29d 0.3± ±1.1 1 Ech vlue is the men of three replictes with the stndrd devition. Any two mens in the sme column followed by the sme letter re not significntly (p>0.05) different by Duncn's multiple rnge tests. Fig. 4. FT-IR spectr of geltin/znonps nnoconposite films. Fig. 5. XRD ptterns of geltin/znonps nnocomposite films. were 89.5±0.7 % nd 28.9±0.9 %, respectively. When ZnONPs were incorported into geltin, the % trnsmittnce vlues of films t 280 nm decresed drsticlly down to 0.3%, but the % trnsmittnce vlues t 660 nm decresed mrginlly with the n increse of ZnONPs concentrtions. The concentrtion of ZnONPs gretly influenced the trnsmittnce vlue of the nnocomposite films. X-ry diffrction (XRD) ptterns of the net geltin nd geltin/znonps nnocomposite films re shown in Fig. 5. The diffrction peks were not observed in cse of net geltin film nd geltin/znnonps nnocomposite films with lower concentrtions of ZnONPs. However, nnocomposite films with high concentrtions of ZnONPs exhibited chrcteristic diffrction peks t 2θ of 31.8, 34.4, 36.2, 47.5, 56.5, 62.8, 67.9, nd 69.1, which correspond to (100), (002), (101), (102), (110), (103), (112), nd (201) plnes of zinc oxide nnoprticles, respectively19). These diffrction peks confirmed the presence of crystlline ZnONPs in nnocomposite films8). Similr results of diffrction peks were observed with ZnO incorported nnocomposites with other polymer mtrix8,18). The intensity of peks ws incresed with n increse in the concentrtion of ZnONPs. FTIR nd XRD nlysis FT-IR nlysis ws crried out to study the interctions between ZnONPs nd geltin mtrix (Fig. 4). The spectr of ll nnocomposite film displyed chrcteristic peks in the rnge of 3500 to 650 cm-1. All films exhibited the bnds of mide I, mide-ii, nd mide-iii t 1631, 1550, nd 1240 cm-1, respectively15). The bnd round 1041 cm-1 ws due to the interction between OH group of glycerol nd geltin16). The brod pek ner 3300 cm-1 ws due to hydrogen bonding17). An increse in intensity of peks ws observed when the concentrtion of ZnONPs incresed. It indicted certin interctions between ZnONPs nd biopolymer mtrix18). Therml stbility The therml stbility of the geltin nd geltin/znonps nnocomposite films ws mesured using thermogrvimetric nlysis. The results of TGA nd DTG curves re shown in

6 46 Shiv Shnkr et l. Kore Journl of Pckging Science & Technology Fig. 6. () TGA nd (b) DTG thermogrms of geltin/znonps nnocomposite films. Fig. 6. All films showed multi steps of therml decomposition in TGA curves. The initil weight loss ws observed round 90 o C due to the removl of moisture from the films. The smll shoulders round o C ws scribed to the therml decomposition of glycerol 20). The third steps of mjor therml decomposition were observed round 320 o C, which cn be ttributed to the therml decomposition of geltin 21). The therml stbility of geltin/znonps nnocomposite films ws incresed with n increse in the concentrtion of ZnONPs. There were no much difference in TGA nd DTG curves of geltin nd geltin/cmc nnocomposite films. The differences in the curve of geltin/znonps nnocomnposite films were due to the presence of ZnONPs. After the finl therml decomposition, the residul percentges t round 600 o C of the net geltin, geltin/cmc, geltin/znonp 0.5, geltin/znonp 1.0, geltin/znonp 1.5, geltin/znonp 2.5 were 23.63, 21.97, 23.76, 28.98, 33.12, nd 36.01%, respectively. Moisture content, wter contct ngle nd wter vpor permebility Tble 2 shows the MC, WCA, nd WVP of the net geltin nd geltin/znonps nnocomposite films. Compred with the net geltin film, geltin/cmc film exhibited slightly lower MC, wheres, MC of geltin/znonps nnocomposite films incresed with n increse in the concentrtion of ZnONPs. The incorportion of ZnONPs into the geltin slightly incresed the WVP of the films. The nnoprticles in the film mtrix exist s discontinuous prticles, which mke the BNC film more porous nd thus incresing the WVP of the polymeric films. In contrst, Knmni nd Rhim 8) obtined the decrese in WVP, when ZnONPs were incorported in vrious nnocomposite films. Moreover, geltin/cmc film showed higher WVP s compred to net geltin film becuse of the hydrophilic nture of CMC. The WCA (degree) of the net geltin film ws 52.4±0.9 nd decresed significntly compred to 48.3±0.9 for geltin/ CMC film (p>0.05). This decrese in WCA ws ttributed to the hydrophilic behvior of CMC. The WCA vlues nnocomposite films incresed linerly fter blending ZnONPs in geltin mtrix. The WCA of films ws incresed with n increse in the concentrtion of ZnONPs used for incorportion in BNC films. This increse in the vlues of WCA ws due to Tble 2. Misture content, wter vpor permebility, nd wter contct ngle of geltin/znonps nnocomposite films Film MC (%) WVP ( 10-9 g.m/m 2.P.s) WCA(º) Geltin 11.1± ± ±0.9 cd Geltin/CMC 10.7± ± ±0.9 Geltin/ZnONP ± ± ±2.4 b Geltin/ZnONP ±0.3 b 1.64±0.08 b 50.8±1.8 bc Geltin/ZnONP ±0.0 b 1.67±0.06 b 53.3±2.0 de Geltin/ZnONP ±0.3 c 2.21±0.09 c 55.3±0.5 e 1 Ech vlue is the men of three replictes with the stndrd devition. Any two mens in the sme column followed by the sme letter re not significntly (p>0.05) different by Duncn's multiple rnge tests.

7 Vol. 20, No. 2 (2014) Geltin/ZnO Nnocomposite films 47 Tble 3. Tensile properties of gel/znonps BNC films using different concentrtions of ZnONPs Film Thickness (ìm) TS (MP) E (%) EM (MP) Geltin 58.2± ±2.1 d 7.3± ±66.8 d Geltin/CMC 59.0± ±3.0 e 7.0± ±90.6 e Geltin/ZnONP ± ±4.6 c 7.3± ±158.2 c Geltin/ZnONP ±1.2 b 40.8±6.4 b 15.4±7.8 b ±212.8 b Geltin/ZnONP ±2.7 b 39.9±4.8 b 22.6±5.6 c ±186.4 b Geltin/ZnONP ±3.0 c 20.6± ±3.2 d 385.2± Ech vlue is the men of three replictes with the stndrd devition. Any two mens in the sme column followed by the sme letter re not significntly (p>0.05) different by Duncn's multiple rnge tests. the incorportion of hydrophobic ZnONPs, which mde the BNC film surfce more hydrophobic 8). Similrly, Nfchi et l. 22) reported tht the ZnO nnorod incorported sgo strch films hd higher wter contct ngle thn the net strch film. They lso found tht the hydrophobicity of the film incresed when high concentrtions of ZnO ws dded into the film. Thickness nd mechnicl properties The thickness of the net geltin film ws 58.2±1.6 µm, which ws incresed to 59.0±1.9, 59.1±2.0, 62.1±1.2, 62.1± 2.7, nd 69.5±3.0 µm for geltin/cmc, geltin/znonp 0.5, geltin/znonp 1.0, geltin/znonp 1.5, nd geltin/znonp 2.5 nnocomposite films, respectively (Tble 3). Similr results of incresed thickness ws observed when ZnONPs ws dded in PVC films 23). The mechnicl properties of the geltin films were lso gretly influenced by the ddition of ZnONPs (Tble 3). The tensile strength nd elstic modulus of the geltin films were incresed when CMC ws dded in geltin. Menwhile, their liner reduction with incorportion of ZnONPs upto concentrtion of 1.5 mm decresed drsticlly with 2.5 mm of Zn ONPs. On the contrry, the elongtion t brek (E) of geltin films incresed significntly with the ddition of ZnONPs. These chnges in TS nd E suggests tht incorportion of ZnONPs in geltin films hs mde some chnges in the structure of geltin mtrix. Antimicrobil ctivity The ntibcteril ctivity of the net geltin film nd geltin/znonps nnocomposite ginst Grm-positive (L. monocytogenes) nd Grm-negtive (E. coli) food pthogenic bcteri is shown in Fig. 7. All ZnONPs incorported films showed strong ntibcteril ctivity ginst L. monocytogenes thn E. coli. Similr results hs been observed by Knmni nd Rhim 8) with ZnONPs incorported vrious polymer films. The ntimicrobil ctivity of ZnONPs ws incresed with increse in the concentrtion of ZnONPs. However, geltin/znonp 1.5 nd geltin/znonp 2.5 showed lmost similr ntibcteril ctivities. The results indicted tht the geltin/znonp 1.5 nnocomposite film showed the best ntimicrobil ctivity mong the films tested. Though the mechnism of the ntimicrobil c- Fig. 7. Antimicrobil ctivities of geltin/znonps nnocomposite films ginst () L. monocytogenes nd (b) E. coli.

8 48 Shiv Shnkr et l. Kore Journl of Pckging Science & Technology tion of the nnocomposite films including ZnONPs hs not been known clerly, it is probble tht the films relese ZnO NPs nd Zn 2+ into the medium which bind with outer cell wll of bcteri nd penetrte through the cell wll of bcteri. The Zn 2+ rect with interior components of cells nd ffects the vibility of the cells 8,22). Conclusion The bio-nnocomposite films of geltin nd ZnONPs were synthesized using solvent csting methods. The effects of vrious concentrtions of ZnONPs on the physicl, mechnicl, nd ntimicrobil properties of nnocomposite films were studied. UV brrier property of geltin film ws enhnced significntly, wheres mechnicl nd wter vpor properties were decresed fter incorporting ZnONPs in the geltin mtrix. The ZnONPs incorported geltin films showed profound ntibcteril ctivity ginst both Grm-positive nd Grm-negtive food-borne pthogens. The ntibcteril nd UV brrier properties incresed with the increse in the concentrtions of ZnONPs. The geltin/znonps nnocomposite films with strong ntimicrobil ctivity nd UV-screening property hve high potentil to be used s n ctive food pckging mterils to mintin the food qulity nd to extend the shelf-life of pckged foods. Acknowledgements This reserch ws supported by the Agriculture Reserch Center (ARC ) progrm of the Ministry for Agriculture, Food nd Rurl Affirs, Kore. References 1. Shnkr, S., Teng, X. nd Rhim, J.W Properties nd chrcteriztion of gr/cunps bionnocomposite films prepred with different copper slts nd reducing gents. Crbohyd. Polym. 114: Khllofufi, S., Gisson, J. nd Rtti C Cn. Agric. Eng. 42: Llorens, A., Lloret, E., Picouet, P.A., Trbojevich, R. nd Fernndez, A Metllic bsed micro nd nnocomposites in food contct mterils nd ctive food pckging. Trends Food Sci. Technol. 24: Knmni, P. nd Rhim, J.W Physicl, mechnicl nd ntimicrobil properties of geltin bsed ctive nnocomposite films contining AgNPs nd nnocly. Food Hydrocoll. 35: Shnkr S. nd Rhim J.W Effect of copper slts nd reducing gents on chrcteristics nd ntimicrobil ctivity of copper nnoprticles. Mt. Lett. 132: Shnkr S., Jiswl L., Aprn R.S.L. nd Prsd R.G.S.V Synthesis, chrcteriztion, in vitro biocomptibility, nd ntimicrobil ctivity of gold, silver nd gold silver lloy nnoprticles prepred from Lnsium domesticum fruit peel extrct. Mt. Lett. In press 7. Espiti, P.J.P., Sores, N.F.F., Coimbr, J.S.R., de Andrde, N.J., Cruz, R.S. nd Medeiros, E.A.A Zinc oxide nnoprticles: Synthesis, ntimicrobil ctivity nd food pckging pplictions. Food Bioprocess Tech. 5: Knmni, P. nd Rhim, J.W Properties nd chrcteriztion of bionnocomposite films prepred with vrious biopolymers nd ZnO nnoprticles. Crbohyd. Polym. 106: Rhim, J.W., Wng, L.F. nd Hong, S.I Preprtion nd chrcteriztion of gr/silver nnoprticles composite films with ntimicrobil ctivity. Food Hydrocoll. 33: Genndios, A., Weller, C.L. nd Gooding, C.H Mesurement errors in wter vpor permebility of high permeble, hydrophilic edible films. J. Food Eng. 21: Rhim, J.W., Hong, S.I., Prk, H.M. nd Ng, P.K.W Preprtion nd chrcteriztion of chitosn-bsed nnocomposite films with ntimicrobil ctivity. J. Agricul. Food Chem. 54: Rhim, J.W. nd Wng, L.F Mechnicl nd wter brrier properties of gr/κ-crrgeenn/konjc glucomnnn ternry blend biohydrogel films. Crbohyd. Polym. 96: Rhim, J.W Effect of PLA lmintion on performnce chrcteristics of gr/-crrgeenn/cly bio-nnocomposite film. Food Res. Int. 51: Kim, D., Jeon, K., Lee, Y., Seo, J., Seo, K., Hn, H. nd Khn, S.B Preprtion nd chrcteriztion of UVcured polyurethne crylte/zno nnocomposite films bsed on surfce modified ZnO. Prog. Org. Cot. 74: Arft, Y.A., Benjkul, S., Prodprn, T., Sumpvpol, P. nd Songtipy, P Properties nd ntimicrobil ctivity of fish protein isolte/fish skin geltin film contining bsil lef essentil oil nd zinc oxide nnoprticles. Food Hydrocoll. 41: Hoque, M.S., Benjkul, S., Prodprn, T. nd Songtipy, P Properties of blend film bsed on cuttlefish (Sepi phronis) skin geltin nd mungben protein isolte. Int. J. Biol. Mcromol. 49: Muyong, J.H., Cole, C.G.B. nd Duodu, K.G Chrcteristion of cid soluble collgen from skins of young nd dult Nile perch (Ltes niloticus). Food Chem. 85: Anith, S., Brbu, B., John Thiruvdigl, D., Goplkrishnn, C. nd Ntrjn, T.S Opticl, bctericidl nd wter repellent properties of electrospun nnocomposite membrnes of cellulose cette nd ZnO. Crbohyd. Polym. 87: Sngeeth, G., Rjeshwri, S. nd Vencktesh, R Green synthesis of zinc oxide nnoprticles by loe brbdensis miller lef extrct: Structure nd opticl properties. Mter. Res. Bull.. 46: Rhim, J.W., Wng, L.F., Lee, Y. nd Hong, S.I Preprtion nd chrcteriztion of bio-nnocomposite films of

9 Vol. 20, No. 2 (2014) Geltin/ZnO Nnocomposite films 49 gr nd silver nnoprticles: Lser bltion method. Crbohyd. Polym. 103: El-Hefin, E.A., Nsef, M.M. nd Yhy, A.H Preprtion nd chrcteriztion of chitosn/gr blended films: prt 2. Therml, mechnicl, nd surfce properties. E-Journl of Chemistry. 9: Nfchi, A.M., Alis, A.K., Mhmud, S. nd Robl, M Antimicrobil, rheologicl, nd physicochemicl properties of sgo strch films filled with nnorod-rich zinc oxide. J. Food Eng. 113: Li, X., Xing, Y., Li, W., Jing, Y. nd Ding, Y Antibcteril nd physicl properties of poly(vinyl chloride)- bsed film coted with ZnO nnoprticles. Food Sci. Technol. Int. 16: