Journal of Food Engineering

Transcription

1 Journl of Food Engineering 96 (2010) Contents lists vilble t ScienceDirect Journl of Food Engineering journl homepge: Development of ntioxidnt food pckging mterils with controlled relese properties Seyhun Gemili, Ahmet Yemenicioğlu b, Scide Alsoy Altınky, * Deprtment of Chemicl Engineering, Fculty of Engineering, Izmir Institute of Technology, Gülbhçe Köyü, Url, Izmir, Turkey b Deprtment of Food Engineering, Fculty of Engineering, Izmir Institute of Technology, Gülbhçe Köyü, Url, Izmir, Turkey rticle info bstrct Article history: Received 20 Mrch 2009 Received in revised form 6 August 2009 Accepted 8 August 2009 Avilble online 23 August 2009 Keywords: Antioxidnt pckging L-tyrosine L-scorbic cid Controlled relese Cellulose cette In this study, cellulose cette (CA) films with different morphologicl fetures were prepred in order to control the relese rtes of low moleculr weight nturl ntioxidnts, L-scorbic cid nd L-tyrosine. Incresing CA content in the csting solution decresed the verge pore size nd porosity of the films, thus, reduced the diffusion rtes of both ntioxidnts through the films. Although both ntioxidnts hve similr moleculr weights, L-tyrosine relesed into wter much more slowly thn L-scorbic cid. The highest ntioxidnt ctivity in relese test solutions ws observed with highly porous L-tyrosine contining films. However, when the porosity of the films reduced, the ntioxidnt ctivity of L-scorbic cid relesed into solution ws found to be higher due to trpping of significnt mount of L-tyrosine in dense films. The use of different ntioxidnts cused different chnges in morphologicl nd mechnicl properties of the CA films. Vrying the structurl fetures of the films with the preprtion conditions or using different surfces of the films llowed the controlled relese of ech ntioxidnt. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Trditionlly, ntimicrobils or ntioxidnts re mixed into initil food formultions, or lterntively foods re dipped into solutions contining these dditives. Limittions of these pproches re: the cese of protection effect once the ctive compounds re consumed in complex rections of food system nd lck of selectivity to trget the food surfce where most microbil nd oxidtive spoilge rections occur intensively. Active pckging cn overcome these limittions by providing continuous relese of functionl dditives from pckging mterils to food surfce, thus, mintining only their criticl concentrtion t the surfce necessry for inhibiting the microbil growth or oxidtive chnge (Appendini nd Hotchkiss, 2002). Controlled relese systems hve been developed nd used extensively for phrmceuticl pplictions (Lnger nd Pepps, 1981; Leong nd Lnger, 1988; Bryden, 2003). Different strtegies for chieving controlled relese of drugs, nd preprtion nd modeling of drug delivery systems hve been reported (Lnger nd Pepps, 1981; Mllprgd nd Pepps, 1997; Richrd, 1998; Siepmnn et l., 1999; Siepmnn nd Pepps, 2001; Arifin et l., 2006). However, the studies in the field of food pckging re very limited lthough controlled relese of ctive gents through food pckging mterils is n essentil feture to provide * Corresponding uthor. Tel.: ; fx: E-mil ddress: scidelsoy@iyte.edu.tr (S.A. Altınky). desired concentrtions on food surfces. Hn nd Floros (1998) re one of the first reserchers who used the concept of controlled relese in food pckging pplictions. They suggested controlling the relese kinetics of ntimicrobils by using multilyer structure which included n outer brrier lyer, mtrix lyer contining the ctive gent nd control lyer. Buonocore et l. (2005) lso developed multilyer films which consist of two externl control lyers nd n inner lyer contining the ctive gent. The sme reserch group hs lso encpsulted the ctive compounds in polymer mtrix nd tried to control the relese rtes by chnging the concentrtion of cross linking gent in the mtrix (Buonocore et l., 2003, 2004). Ozdemir nd Floros (2003) formed controlled relese system by dispersing hydrophobic wx prticles within hydrophilic film mtrix, thus, incresing hydrophobicity nd tortuosity of the films ginst the diffusion of n ntimicrobil gent. LCoste et l. (2005) hve proposed using smrt blending technique to develop controlled relese pckging mterils. Recently, our reserch group showed the suitbility of using symmetric cellulose cette (CA) films for controlled relese of lysozyme, nturl ntimicrobil enzyme used in food preservtion (Gemili et l., 2009). The relese rte of the ctive gent through these types of films is controlled with the porosity nd degree of symmetry of the films which cn be esily modulted by chnging the film csting conditions (Altinky nd Yenl, 2006; Gemili et l., 2009). The ppliction of either porous or dense sides of the films on food surfce is lso gret dvntge to control relese rtes in different food systems. In this study, we imed to /$ - see front mtter Ó 2009 Elsevier Ltd. All rights reserved. doi: /j.jfoodeng

2 326 S. Gemili et l. / Journl of Food Engineering 96 (2010) Nomenclture A f re of the film (cm 2 ) D effective diffusion coefficient of ctive gent in the film (cm 2 /s) K prtition coefficient (cm 3 solution/cm 3 film) L thickness of the film (cm) M t totl mount of ctive gent desorbed from the film t nytime t (g) M 1 totl mount of ctive gent desorbed from the film t equilibrium (g) t time (sec) V sol volume of the solution (cm 3 ) show the potentil of symmetric CA films for controlled relese of different functionl gents, thus, we hve developed films including nturl ntioxidnts, L-scorbic cid nd L-tyrosine. These substnces were selected prticulrly since they re powerful ntioxidnts with close nd low moleculr weights (L-scorbic cid: g/mol, L-tyrosine: 18 g/mol), but very different hydrophilic/hydrophobic properties which llow using them in vrious food systems. The scorbic cid is highly polr, cidic compound whose ntioxidnt ctivity comes from its reducing power relted to its 2,3-enediol moiety (Gregory, 1996). It is used frequently during curing of mets nd miniml processing of fresh fruits nd vegetbles to inhibit enzymtic browning ctlyzed by polyphenoloxidse (PPO) enzyme (Gregory, 1996; Vmos-Vigyzo, 1981). On the other hnd, L-tyrosine is n ntioxidnt mino cid which hs mphiphilic properties due to its polr nd polr groups. Similr to the other romtic mino cids, phenyllnine nd tryptophn, the ntioxidnt ctivity of L-tyrosine is due to its side chin which is cpble to donte protons to free rdicls (Rjpkse et l., 2005). The L-tyrosine is not commercilly used in food pplictions. However, there is gret interest in food industry to use ntioxidnt proteins, peptides nd mino cids s food ntioxidnts (Arcn nd Yemenicioglu, 2007). 2. Mterils L-scorbic cid nd L-tyrosin were purchsed from Merck (Drmstdt, Germny). ABTS (2,2-zino-bis-(3-ethylbenz-thizoline-6-sulfonic cid)) ws purchsed from Sigm Chem. Co. (St. Louis, MO, USA). Trolox ((±)-6-hydroxy-2,5,7,8-tetr-methylchromne-2-crboxylic cid) ws purchsed from Fluk (Switzerlnd). Cellulose cette with moleculr weight of 50,000 nd cetyl content of 39.8% ws obtined from Estmn (Kingsport, TN, USA). Acetone (99%) ws obtined from Merck (Drmstdt, Germny). 3. Methods 3.1. Preprtion of the films To prepre the films, cellulose cette (CA) dissolved in cetone nd ntioxidnt gents dissolved in distilled wter were mixed in tightly closed nd seled bottle for 30 min t 920 rpm. The weight percentges of cetone nd ntioxidnts in the solution were kept constnt t 80% nd 1.5%, respectively, while CA nd wter concentrtions were chnged to obtin films with different morphologies. The mixed solution ws then cst on polypropylene substrte by using n utomtic film pplictor (Sheen, Automtic film pplictor-1133n, Kigston, Englnd) t speed of 100 mm/s. The wet thicknesses of the films were djusted by four-sided film pplictor with gp size of 300 microns. The cst film ws then immeditely trnsferred into n environmentl chmber (Siemens, Simtic OP7, Mss Mrtn, Itly) nd dried for 30 min t 25 C nd 40% reltive humidity Relese tests The relese tests were conducted by using hnd mde glss pprtus for both dense nd porous sides of the films. In this pprtus, film smples (5 cm in dimeter) were squeezed between two glss pltes. One of the pltes hs circulr hole with dimeter of 4 cm t the center, nd in order to contct just one surfce of the film with wter, two silicon o-rings (full dimeter: 6 cm, inside dimeter: 4 cm) were plced on both sides of the films. The detils of the pprtus were given by Gemili et l. (2009). For relese studies, the pprtus ws plced into glss Petri dish (10 cm in dimeter) contining 50 ml distilled wter t 4 C nd stirred mgneticlly t 240 rpm with 2 cm long Teflon coted rod. To prevent evportion during relese period, the petri dishes were covered tightly first with prfilms nd then with their glss lids. The ntioxidnt ctivities in relese medium were monitored by tking ml smples t different time periods nd mesuring ctivity three times by using ABTS decoloriztion ssy given in Section 3.3. The relese tests were continued until equilibrium condition is reched Determintion of soluble ntioxidnt ctivity Bsed on free rdicl-scvenging ctivity, the ntioxidnt ctivity ws determined s described in Re et l. (1999), by using ABTS free rdicl solution prepred by oxidtion with potssium persulfte. The rection mixtures for the mesurements were formed by mixing 0.1 ml of smple from relese test medium nd 2.4 ml of ABTS free rdicl solution diluted with phosphte buffer solution (initil bsorbnce ws lmost 0.7 t 734 nm). The discolortion of drk blue-colored ABTS free rdicl by the ntioxidnt ws monitored t 734 nm for 6 min t 30 C. Percentge inhibitions of ABTS free rdicl were then clculted nd converted to trolox ( stndrd ntioxidnt which is vitmin E nlogue) equivlents by using stndrd curves. The vlues obtined were divided by the re of the films to determine relesed ntioxidnt ctivity s lmole trolox per cm 2. All mesurements were performed in triplicte Determintion of immobilized ntioxidnt ctivity Following the relese tests conducted in distilled wter, the free rdicl-scvenging ctivity of ntioxidnt gents trpped in the films ws lso determined. For this purpose, the films were cut into two pieces nd ech piece ws then plced into different Petri dishes contining 25 ml of ABTS free rdicl solution. The rections were conducted in n incubtor t 30 C under continuous mgnetic stirring nd the decrese in bsorbnce t 734 nm ws monitored periodiclly. Percentge inhibition of ABTS free rdicl fter 60 min ws then clculted nd converted to trolox equivlents. The immobilized ntioxidnt ctivity ws reported s lmole trolox per cm 2. All mesurements were performed in triplicte.

3 S. Gemili et l. / Journl of Food Engineering 96 (2010) Morphologicl chrcteriztion of the films A scnning electron microscope (SEM) (Philips XL-30S FEG, FEI Compny, Eindhoven, The Netherlnds) ws used to chrcterize the morphology of the films. Film smples were coted with gold plldium using Mgnetron Sputter Coting Instrument (VG Microtech, Englnd). Two pictures were tken for ech film. After the SEM pictures were tken, totl thickness, dense skin lyer thickness, porosity, nd pore size of the films were mesured with the id of softwre (Scndium universl SEM imge pltform) in the computer connected to the SEM. Five to 10 mesurements were tken for ech film to determine totl nd dense skin lyer thicknesses. Two porosity mesurements were conducted for ech type of film. For the pore size mesurement, lmost 30 pores were selected in ech SEM picture nd the dimeters of the pores were mesured. The porosities (%) were mesured utomticlly by differentiting the colors of porous nd non-porous res of the films. The thickness of the dense skin lyers ws mesured utomticlly by selecting these clerly distinguishble regions mnully Mechnicl properties of the films The tensile strength of the films ws mesured with Testometric M kN (Lncshire, Englnd) testing mchine in ccordnce with ASTM D stndrd. Smples 5 mm in width nd 50 mm in guge length were strined t constnt rte of 5 mm/min until filure. At lest, five specimens were used for the tests nd plot of stress versus strin ws utilized to clculte the tensile properties of the films Determintion of diffusion coefficients of L-tyrosine nd L-scorbic cid To determine diffusion coefficient of ntioxidnts, Fick s second lw ws used which describes the chnge in the concentrtion of ntioxidnt gents in the films with respect to time nd position. To be ble to use Fick s second lw, it ws ssumed tht there is no chemicl rection between the ctive compound nd the film, mss trnsfer in the film tkes plce only by diffusion nd diffusion coefficient of ctive compound in the film, D, is constnt. A solution of Fick s second lw long with one initil nd two boundry conditions is presented in clssicl book of Crnk (1975). The most prcticl expression obtined from this solution which gives the totl mount of ctive compound desorbed from the film t ny time t, M t, normlized with respect to the mount desorbed t equilibrium, M 1, is given below: M t M 1 ¼ 1 X1 n¼1 2ð1 þ Þ exp Dq 1 þ þ 2 2 q 2 n t=l2 n where ¼ V sol KA f L, nd the q ns re the non-zero positive roots of tn q n ¼ q n. To determine the diffusion coefficients of ntioxidnts, the ntioxidnt ctivity dt obtined during relese tests were first converted to concentrtion dt by using clibrtion curves formed for L-tyrosine nd L-scorbic cid. Then, the diffusivities were clculted itertively by minimizing the difference between Eq. (1) given bove nd experimentl uptke curves Sttisticl nlysis The sttisticl nlysis ws conducted by evluting dt with nlysis of vrince (ANOVA). Vlues re significntly different t p < 5 s determined by Fisher s protected lest significnt difference. ð1þ 4. Results nd discussions 4.1. The morphology of the films Recently, our reserch group successfully developed symmetric CA films for controlled relese of ntimicrobil enzyme lysozyme by dry phse inversion technique (Gemili et l., 2009). This technique llows to crete film morphologies rnging from dense to highly symmetric nd porous ones by chnging film preprtion conditions. In this work, we hve used the sme technique to prepre CA films contining low moleculr weight nturl ntioxidnts, L-scorbic cid nd L-tyrosine, nd controlled their relese rtes by vrying the porosity nd degree of symmetry of the films. To control such morphologicl fetures, we hve chnged the composition of the film forming solution. Fig. 1 c illustrte the influence of the initil csting composition on the structure of L-scorbic cid contining films through SEM pictures. In these pictures, the dense nd porous surfces exist on top nd bottom sides of the double rrows which show the totl thickness of the films. Chrcteristics of these films determined from the nlysis of SEM imges were lso listed in Tble 1. As expected, both L- scorbic cid nd L-tyrosine contining films prepred with the lowest CA concentrtion (5%) hve the highest porosities including mcrovoids, with n immesurble thin dense skin lyer t the top surfces. On the other hnd, incresing CA/cetone rtio in the csting solution leds to the formtion of less porous structure with thicker dense skin lyers nd reduced pore sizes. The results in Tble 1 indicte tht the ntioxidnt type cused significnt differences in the porosity of the films while the pore size nd dense skin lyer thicknesses were found to be sttisticlly different only for the films prepred with 10% nd 15% CA, respectively Effect of film composition on relesed ntioxidnt ctivity To determine the effect of film composition on relesed ntioxidnt ctivity, porous or dense surfces of CA films were brought into contct with distilled wter. The relese tests were conducted t +4 C since the objective of this work is to develop ctive pckging mterils for refrigerted foods. Figs. 2 nd 3 show the increse of ntioxidnt ctivity in distilled wter becuse of L-scorbic cid nd L-tyrosine relese from the films, respectively. Although both ntioxidnts hve similr moleculr weights, the L-tyrosine releses into wter much more slowly thn the L-scorbic cid. The L-tyrosine is considerbly more hydrophobic thn the highly polr L-scorbic cid. Therefore, its ffinity to hydrophobic CA films nd dely in the relese rte of this compound is quite expected. Moreover, it is lso likely tht the six crbon romtic ring of L-tyrosine which is bulkier thn tht of four crbon ring of scorbic cid fces greter diffusion brrier effect due to higher tortuosity of the film. In most films, ntioxidnt relese from porous surfces occurred more rpidly thn tht from dense surfces. The L-tyrosine contining films prepred with 5% CA gve lmost 2.5-fold higher mximum relesed ntioxidnt ctivity thn similr films contining L-scorbic cid (Tble 2). This occurred due to lmost 4-fold greter ntioxidnt cpcity of L-tyrosine thn L-scorbic cid. According to the slopes of inhibition vs. concentrtion curves obtined for the ntioxidnts, 1 lmole of L-scorbic cid nd L-tyrosine equl to 9 nd 1.18 lmole of trolox, respectively (Fig. 4). When the porosity of the films reduced by incresing their CA content, the mximum ntioxidnt ctivity of L-scorbic cid relesed into solution ws found to be higher. This suggests high diffusion rte of L-scorbic cid through much more dense films with reduced pore size nd porosity, but trpping of significnt mount of L-tyrosine in these dense films. The mximum L-tyrosine ntioxidnt ctivities relesed from dense nd porous

4 328 S. Gemili et l. / Journl of Food Engineering 96 (2010) Fig. 1. SEM of the cross-sections of different symmetric cellulose cette films (CA/cetone/wter/L-scorbic cid weight percentges in film forming solutions: () 5/80/ 13.5/1.5, (b) 10/80/8.5/1.5, nd (c) 15/80/3.5/1.5, Mgnifictions, 3000, upper sides of the films re the dense surfces, while, bottom sides re porous surfces). surfces were significntly different except from the film prepred with 5% CA. This cn be explined by physicl hindrnce of smll pores present on the dense surfces ginst the lrge romtic ring structure of L-tyrosine, consequently, its trpping within the mtrix. In the cse of L-scorbic cid, the use of dense nd porous surfces of only 15% CA contining films cused significnt difference in mximum ntioxidnt relese into the solution Effect of film composition on immobilized ntioxidnt ctivity Following relese tests in distilled wter, ll films were lso tested for immobilized ntioxidnt ctivity to estimte the mount of ntioxidnt trpped or bind within their mtrix. In generl, L-tyrosine contining films showed greter immobilized ntioxidnt ctivity thn L-scorbic cid contining films (Tble 3). The films prepred with 5% CA nd contining L-tyrosine showed similr immobilized ntioxidnt ctivities when their porous or dense surfces were employed in the relese tests before ctivity mesurements. In contrst, the immobilized ntioxidnt ctivities of the films contining 10% nd 15% CA were found to be significntly higher (p < 5) when the films were exposed to relese test with their dense surfces. Apprently, this occurs due to more trpped or bind L-tyrosine remined in this cse. In contrst, in the cse of L-scorbic cid, the immobilized ctivities were mesured significntly higher when the porous rther thn the dense surfces of the films were used in the relese tests (p < 5). The L-scorbic

5 S. Gemili et l. / Journl of Food Engineering 96 (2010) Tble 1 Morphologicl chrcteristics of ntioxidnt contining cellulose cette films. Composition (w%) Totl thickness (lm) b Dense lyer thickness (lm) c Pore size (lm) c Porosity (%) c L-scorbic cid contining films 5/80/13.5/ ± 0 b 8 ± 9 b ± 3 10/80/8.5/ ± ± ± ± 2.5 b 15/80/3.5/ ± ± 0.12 c 0 ± ± c L-tyrosine contining films 5/80/13.5/ ± b 1.15 ± 0.17 b ± 1.68 d 10/80/8.5/ ± ± 3 0 ± 5 c ± 9 e 15/80/3.5/ ± ± 0.52 d 0.50 ± ± 5.94 f Weight percentges of CA/cetone/wter/ntioxidnt gent in film forming solutions. b No sttisticlly significnt differences exist for vlues in this column (p > 5). c Different letters in ech column indicte sttisticlly significnt differences (p < 5). Relesed ntioxidnt ctivity (µmole trolox/cm 2 ) Time (hour) Fig. 2. Initil chnge of ntioxidnt ctivity in distilled wter during relese of L-scorbic cid from different cellulose cette films incubted t 4 C (CA/cetone/wter/ L-scorbic cid weight percentges in film forming solutions: d 5/80/13.5/1.5-porous surfce, s 5/80/13.5/1.5-dense surfce,.10/80/8.5/1.5-porous surfce, 10/80/8.5/ 1.5-dense surfce, j 15/80/3.5/1.5-porous surfce, nd h 15/80/3.5/1.5-dense surfce). Relesed ntioxidnt ctivity (µmole trolox/cm 2 ) Time (hour) Fig. 3. Initil chnge of ntioxidnt ctivity in distilled wter during relese of L-tyrosine from different cellulose cette films incubted t 4 C (CA/cetone/wter/L-tyrosine weight percentges in film forming solutions: d 5/80/13.5/1.5-porous surfce, s 5/80/13.5/1.5-dense surfce,.10/80/8.5/1.5-porous surfce, 10/80/8.5/1.5-dense surfce, j 15/80/3.5/1.5-porous surfce, nd h 15/80/3.5/1.5-dense surfce). cid relesed redily from both dense nd porous surfces of the films. Therefore, no significnt grdient in concentrtion of trpped ntioxidnt occurs through dense to porous sides of the films. In this cse, it is expected to hve higher immobilized L-scorbic cid ntioxidnt ctivity on porous sides due to their greter contct re with the free rdicl solution.

6 330 S. Gemili et l. / Journl of Food Engineering 96 (2010) Tble 2 Antioxidnt ctivities obtined form different CA films during relese tests. Composition (w%) Film surfce Mximum relesed ntioxidnt ctivity-rection period 6 min (lmole trolox/cm 2 ) b Recovery (%) d L-scorbic cid contining films 5/80/13.5/1.5 Porous 1.18 ± 3 (36) c b 90 Dense 1.19 ± 1 (66) b 85 10/80/13.5/1.5 Porous 1.43 ± 3 (126) 95 Dense 1.42 ± 4 (126) 87 15/80/13.5/1.5 Porous 1.33 ± 9 (66) f 82 Dense 1 ± 3 (246) c 63 L-tyrosine contining films 5/80/13.5/1.5 Porous 3.05 ± 4 (1701) e 89 Dense 3.04 ± 3 (1520) e 68 10/80/13.5/1.5 Porous 1.16 ± 1 (1698) b 26 Dense 0.34 ± 1 (1455) d /80/13.5/1.5 Porous 2 ± 4 (1464) c 24 Dense 0.33 ± 0 (126) d 15 Weight percentges of CA/cetone/wter/ntioxidnt gent in film forming solutions. b Different letters in column indicte sttisticlly significnt differences (p < 5). c Incubtion time (minute) to rech mximum ntioxidnt ctivity during relese tests. d (Mximum relesed ntioxidnt ctivity/antioxidnt ctivity incorported) % Inhibition of ABTS free rdicl L-A scorbic cid L-Tyrosine Trolox Concentrtion (µmole/ml) Fig. 4. Antioxidnt ctivities of L-scorbic cid nd L-tyrosine compred to stndrd ntioxidnt trolox. Tble 3 Immobilized ntioxidnt ctivities of films fter relese tests. Composition (w%) Film surfce used in relese test Immobilized ntioxidnt ctivity-rection period 60 min (lmole trolox/cm 2 ) b L-scorbic cid contining film L-tyrosine contining film 5/80/13.5/1.5 Porous 1.10 ± ± 4 bc Dense 0.75 ± 0 d 2.09 ± 2 bc 10/80/13.5/1.5 Porous 1.18 ± ± 2 c Dense 5 ± 0.13 e 2.14 ± 7 b 15/80/13.5/1.5 Porous 1.91 ± 9 bc 1.83 ± 2 c Dense 6 ± ± 2 b Weight percentges of CA/cetone/wter/ntioxidnt gent in film forming solutions. b Different letters in columns (evluted together) indicte sttisticlly significnt differences (p < 5) Effect of film composition on diffusion coefficients of ntioxidnts The normlized releses of L-tyrosine nd L-scorbic cid from CA films into wter t 4 C were given in Figs. 5 nd 6, respectively. These curves were obtined by plotting the rtio of the mount of the ntioxidnt gents relesed t time t, M t, to the totl mount relesed when equilibrium is reched, M 1. Tble 4 lso listed the effective diffusion coefficients of the ntioxidnt gents nd their prtition coefficients clculted from the normlized relese curves using Eq. (1) nd the equilibrium condition, respectively. In generl, the diffusion coefficient of L-tyrosine is smller thn tht of L-scorbic cid. In most cses, the diffusivities were higher when the porous side of the films ws in contct with wter. The diffusion rtes of L-scorbic cid through either surfce of the film prepred with 5% CA were found sme since this film hs highly porous nd lmost symmetric structure. Similr diffusivities were lso obtined for L-tyrosine t ech surfce of the film cst with 15% CA. This film hs highly dense structure where the

7 S. Gemili et l. / Journl of Food Engineering 96 (2010) A B M t /M inf M t /M inf Experimentl Theoriticl Experimentl Theoriticl Time (minute) Time (minute) Fig. 5. Experimentl nd theoreticl frctionl mss relese of L-tyrosine from cellulose cette films (CA/cetone/wter/L-scorbic cid weight percentges in film forming solutions: (A) 5/80/13.5/1.5-porous surfce nd (B) 5/80/13.5/1.5-dense surfce). A B M t /M inf M t /M inf Experimentl Theoriticl Time (minute) Experimentl Theoriticl Time (minute) Fig. 6. Experimentl nd theoreticl frctionl mss relese of L-scorbic cid from cellulose cette films (CA/cetone/wter/L-tyrosine weight percentges in film forming solutions: (A) 15/80/3.5/1.5-porous surfce nd (B) 15/80/3.5/1.5-dense surfce). Tble 4 Effective diffusion nd prtition coefficient of ntioxidnt gents in different cellulose cette films. Composition (w%) Film surfce Prtition coefficient D (cm 2 /s) L-scorbic cid contining films 5/80/13.5/1.5 Porous Dense /80/8.5/1.5 Porous Dense /80/3.5/1.5 Porous Dense L-tyrosine contining films 5/80/13.5/1.5 Porous Dense /80/8.5/1.5 Porous 10, Dense 39, /80/3.5/1.5 Porous 12, Dense 22, Weight percentges of CA/cetone/wter/ntioxidnt gent in film forming solutions. frction of dense skin lyer is lmost 35% of totl thickness, thus, the bulky L-tyrosine diffuses t the sme rte when the film surfces in contct with wter were chnged. It should lso be noted tht the diffusivities of ntioxidnts decresed with the incresed CA content of the films due to chnge in the structure of the films from highly porous nd symmetric to dense nd symmetric ones. An unexpectedly low diffusivity of L-tyrosine ws obtined through the dense side of the film prepred with 10% CA. This my be explined by effective blocking of pores on the dense surfce by L-tyrosine molecules diffused from porous to dense side nd trpped within these pores. Prtition coefficients of L-tyrosine were found higher thn those of L-scorbic cid due to higher ffinity of hydrophobic romtic ring of this ntioxidnt to CA which hs lso hydrophobic nture Effect of film composition on mechnicl properties of the films The mechnicl properties of the films were given in Tble 5. The results indicte tht for ech film type tensile strength nd Young s modulus vlues incresed significntly (p < 5) with incresing CA content in initil film forming solution. This is due to reduced porosities, pore sizes nd the chnge in film structures from porous to dense ones. Except the control films, elongtion vlues of the films did not correlte with the CA content. The results in Tble 5 indicte tht compred with the control films,

8 332 S. Gemili et l. / Journl of Food Engineering 96 (2010) Tble 5 Mechnicl properties of developed cellulose cette films. Composition (w%) Elongtion (%) c Tensile strength (MP) c Young s modulus (MP) c Control films b 5/80/15/ ± 1 d ± 1.61 c ± /80/10/ ± ± ± c 15/80/5/ ± 1.58 f ± 3.75 b ± d L-scorbic cid contining films 5/80/13.5/ ± 0.78 ce 6.18 ± 1.54 c 165 ± 41 10/80/8.5/ ± 6 de 33 ± ± 204 b 15/80/3.5/ ± 2.69 g ± b 2527 ± 261 e L-tyrosine contining films 5/80/13.5/ ± 0.35 bd 2.50 ± 4 c 274 ± 48 10/80/8.5/ ± 3 e ± ± 111 d 15/80/3.5/ ± 6 bcd ± 9.48 d 2716 ± 173 f Weight percentges of CA/cetone/wter/ntioxidnt gent in film forming solutions. b Dt of control films prepred with the sme procedure explined in this work were obtined from our previous study (Gemili et l., 2009). c Different letters in ech column indicte sttisticlly significnt differences (p < 5). the use of L-scorbic cid did not cuse ny significnt chnge in the tensile strength, while in the cse of L-tyrosine significnt reduction ws observed in the tensile strengths of films cst with 15% CA. Young s modulus of the films were significntly ffected by the ddition of ntioxidnts except the most porous films contining the lowest CA content. The use of L-tyrosine cused significnt reduction in elongtion only t 15% CA content, while significnt chnges, reduction or increse, in this prmeter occurred t ll CA concentrtions when L-scorbic cid ws used s ntioxidnt. 5. Conclusion In conclusion, this study clerly showed the good potentil of using symmetric cellulose cette films for controlled relese of L-scorbic cid nd L-tyrosine. Chnging the composition of the csting solution to control the degree of symmetry nd pore size of the films nd ppliction of either dense or porous sides of the films on food surfces re key points to obtin desired relese rtes for the ntioxidnts, hence, to increse the qulity nd shelf life of the foods. Further studies re needed to develop novel food pckging pplictions by testing the effectiveness of the developed films on selected food surfces. 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