PaPer Ital. J. Food Sci., vol. 27 - 2015 1 - Keywords: Coating, edible protein films, permeability, smoked fish, texture - The physicochemical properTies of edible proTein films s. oĞUr1*, n. erkan2 1 Bitlis Eren University, Engineering-Architecture Faculty, Department of Food Engineering, Bes Minare Mah., Ahmet Eren Bulvari, Kampus Yerleskesi, 13000 Bitlis, Turkey 2 Istanbul University, Faculty of Fisheries, Department of Seafood Processing and Quality Control, Ordu Cad., No: 200, 34470 Laleli-Istanbul, Turkey *Corresponding author: Tel. (+90 0434) 2283377-241; Fax (+90 0434) 2283378, email: sdogur@beu.edu.tr AbstrAct In the present study, edible films from isolated or concentrated protein sources and from pro- teins of two different fish species were produced. the texture properties, light transmission (Lt) and oxygen permeability (OP) of producing films were determined. the cL film settled in the sec- ond range according to both tension test parameters, thus outclassing the other tested films. the WG film possessed the lowest Lt, so making it more effective in protecting of food products from light than the other tested films. the sPI film with the lowest OP value can be used for the pur- pose of protecting of food products from harmful effects of oxidation. 2 Ital. J. Food Sci., vol. 27 - 2015 1. IntrOductIOn Edible films and coatings are thin layers that can be eaten with food. they are derived from natural sources and are formed on the surface of a food for the purpose of protecting food and to prolong its shelf-life. For this agricultural function, protective coatings were improved as an alternative to commercial packaging materi- als such as glass, tin and polymer. Edible films and coatings do not carry carcinogen risk and do not cause a waste problem, which are impor- tant problems with plastic-based food packaging. If edible films are prepared in appropriate con- ditions, they can perform all the functions of a useful package. Edible films are prepared utilizing hydrocolloids (protein and polysaccharide), lipids and composites (hydrocolloid+lipid). Edible pro- tein films are separated, however, into two groups: plant origin proteins (corn zein, wheat gluten, soy protein, pea protein, sunflower protein, peanut protein and cotton protein, etc.) and animal ori- gin proteins (keratin, collagen, gelatin, fish my- ofibrillar protein, egg white protein, casein and whey protein, etc.). Edible protein films can be manufactured from isolates or concentrated pro- tein products that are purified from various pro- tein sources, and by the evaluation of processing waste products (rHIM and nG, 2007). the use of edible films for food is very old. so far, the most important application of edible films and coatings is an emulsion, made from oil and waxes (in 1930) that protect the important fea- tures of fruits such as brightness and color, pre- vents complications such as softness, initialing paleness and for improving fungicides, to bet- ter control the maturation and to delay water loss (dEbEAuFOrt et al., 1998; bALdWIn, 1999). the advantages of natural biopolymer films can be summarized as follows: they are edible and biodegradable; to supplement the nutrition- al value of foods; enhance organoleptic charac- teristics of food, such as appearance, odor, and flavor; reduce packaging volume, weight and waste; incorporate antimicrobial agents and antioxidants; extended shelf-life and improved quality of usually non-packaged items; control over inter-component migration of moisture, gases, lipids, and solutes; individual packaging of small particulate foods, such as nuts and rai- sins; function as carriers for antimicrobial and antioxidant agents; for microencapsulation and controlled release of active ingredients; and have a possible use in multilayer food packaging ma- terials together with non-edible film. they are low-cost and abundant; annually renewable re- sources (KrOcHtA, 2002). despite the positive effects in the literature (GEnnAdIOs et al., 1997), the industrial appli- cation of edible films is not very common yet. the theoretical, experimental studies related to different polymers will be used to compose ed- ible films or coatings (using fresh, frozen, pro- cessed products and determining the permeabil- ity properties of films) are currently underway. In the present study were used soy protein iso- lates (sPI), whey powder protein (WP), egg white powder protein (EWP), wheat gluten (WG), corn zein (Z), cattle gelatin (G) and collagen (cL), as well as rainbow trout protein (rtP) and Atlan- tic mackerel protein (MP) as the protein source. the texture properties, the light transmission and the oxygen permeability of edible films pro- duced from these sources were established. 2. MAtErIAL And MEtHOds 2.1. Edible protein film manufacturing the materials for the production of edible pro- tein film were obtained from the smart chemi- cals company (Izmir, turkey). the edible protein films were manufactured as explained below, by pouring a determined amount film of solution into a teflon pan (18 cm×18 cm), drying for a de- termined time and at a determined temperature. 2.1.1. soy protein isolates (sPI) film 5 g sPI (produced in Germany and contain- ing 90% protein), 100 mL distilled water and 2.5 mL glycerol (GLY) was stirred for 15-20 minutes at 55-60ºc. this solution was then stirred for another 10-15 minutes at 75-80 ºc and filtered through a cloth, after the solution’s pH was ad- justed to 10.5±0.1 with 2 M sodium hydroxide (naOH) solution (dEnAVI et al., 2009). Prepared film solution (70 mL) was poured into a teflon pan and dried for 24 hours at 35°c. 2.1.2. Whey protein (WP) film 5 g WP (produced by Lactoprot company in Germany and containing 80% protein), 100 mL distilled water and 5 mL GLY was stirred for 15-20 minutes at 55-60ºc. this solution then was stirred for another 15-20 minutes at 75-80 ºc and filtered through a cloth, after the solu- tion’s pH was adjusted to 8.0±0.1 with 2 n naOH (sArIKus, 2006). the WP film solution (70 mL) was poured into a teflon pan and dried for 48 hours at 35°c. 2.1.3. Egg white powder protein (EWP) film 9 g EWP (produced in turkey and containing 80% protein), 100 mL distilled water, 4.5 mL GLY was stirred for 5 minutes at room temper- ature. then the solution’s pH was adjusted to 11.25±0.1 with 1 n naOH. the solution was kept for 20 minutes in a water bath at 45 ºc and fil- tered through a cloth (GEnnAdIOs et al., 1997). the prepared film solution (70 mL) was poured into a teflon pan and dried for 24 hours at 35°c. Ital. J. Food Sci., vol. 27 - 2015 3 2.1.4. Wheat protein (gluten-WG) film 7.5 g WG (produced in belgium and contain- ing 75-82% protein), 55 mL 95% ethyl alcohol, 45 mL distilled water and 3.75 mL GLY was stirred for 15 minutes at 55 ºc. the solution’s pH was adjusted to 4.0±0.1 with 50% acetic acid. the solution was filtered through a cloth, then stirred for another 15 minutes at 70 ºc (tAnA- dA-PALMu, 2000). All the prepared film solution was poured into a teflon pan and dried for 48 hours at 45°c. 2.1.5. corn protein (zein-Z) film the film solution was prepared from zein pro- tein (produced by sigma Aldrich in usA and con- taining 90% protein), by modifiying the method developed by bAYsAL et al. (2009). 2.5 g Z, 60 mL 95% ethyl alcohol, 1 mL GLY was stirred for 30 minutes at 75-80 ºc (bAYsAL et al., 2009). the pH of the prepared Z film solution was measured as 5.8. the Z film solution (40 mL) was poured into a teflon pan and dried for 24 hours at 45°c. 2.1.6. Gelatin (G) film 2 g G (produced by rousselot company in Ar- gentina and containing 83% protein), 100 mL distilled water, 1.1 mL GLY was stirred for 30 minutes at 55-60 ºc. the solution was then fil- tered through a cloth (tHOMAZInE et al., 2005). the pH of the prepared G film solution was de- termined as 5.1. the G film solution (130 mL) was poured into a teflon pan and dried for 48 hours at 45°c. 2.1.7. collagen (cL) film 3 g cL (produced in turkey and containing 90% protein), 200 mL 3% acetic acid, 1.5 mL GLY was stirred for 30 minutes at 75-80 ºc (HO et al., 2001). When prepared according to this method, the pH of the cL film solution was 3.3. All the prepared film solution was cast into tef- lon pan and dried for 24 hours at 45°c. 2.1.8. rainbow trout protein (rtP) film rainbow trout (Oncorhynchus mykiss) were obtained from the Istanbul Fish market. the fish were transported in ice to the laboratory. the gutted and beheaded fish were minced, af- ter skinning. the fish mince was washed 2-3 times to remove the water-soluble proteins, blood and dirty components, by keeping it for 5-10 minutes in cold water (water:fish ratio of 4:1, w/w). Following the washing process, fish mince was pressed through a cloth in order to remove water. Prepared in this way, washed fish mince constituted the raw material for the edible fish film. Previously produced edi- ble film were tested for protein and moisture in this mince. the rtP ratio was found to be 18.48%, and the moisture ratio was found to be 73.35%. because the protein ratio of the fish mince should be 2%, it was adjusted by adding the necessary amount of distilled wa- ter and then GLY at a ratio of 50% of the pro- tein ratio was added. the mixture was blended and filtered. the solution’s pH was adjusted to 3 with 50% acetic acid, after the solution was stirred for 10-15 minutes at 75-80 ºc. the solu- tion was stirred for another 10-15 minutes at 75-80 ºc (cuQ et al., 1997). the prepared film solution (100 mL) was poured into a teflon pan and dried for 24 hours at 35°c. 2.1.9. Atlantic mackerel protein (MP) film used in manufacturing of edible film, Atlantic mackerel minces (Scomber scombrus) were pre- pared by cleaning and washing, as in the case of rainbow trout flesh. the MP ratio was found to be 23.38%, and the moisture ratio was found to be 72.62%. the MP film manufacturing meth- od was similar to the rtP film manufacturing method. the only difference was that less dis- tilled water was added, as when adjusting the protein ratio was to 2%, because of the MP ratio was higher. the film solution’s pH was adjusted to 3 again (cuQ et al., 1997). the MP film solu- tion (100 mL) was poured into a teflon pan and dried for 24 hours at 35°c. 2.2. The texture Profile of the films tension tests were made for the purpose of determining the resistance of the film against breakage and tensile forces. test measurement values were as follows: target type: distance, test type: tension, target value: 40-90 mm, trigger load: 0.04 n, test speed: 0.5 mm/second, return speed: 4.5 mm/second, probe type: tA3/100, fixture: tA-dGA, load cell: 1500 g. the meas- ured parameters were the tensile force (n) and the maximum elongation (mm). three measure- ments were taken from three protein films be- long to each group. 2.3. The Light Transmission (LT) of the films the Lt of edible protein films was measured according to the method in AstM (2009) by us- ing working visible position dual beam spectro- photometer at 560 nm, at 23±2 ºc. this test method covers the measurement of the trans- parency of plastic sheeting in terms of regular transmittance (t r ). Although generally applica- ble to any translucent or transparent materi- al, it is principally intended for use with nom- inally clear and colorless thin sheeting. three measurements were taken from three protein films belong to each group. the Lt of the films was calculated with the formula below accord- 4 Ital. J. Food Sci., vol. 27 - 2015 ing to light intensity value, measured by equip- ment (AstM, 2009). t r = (I r /I 0 ) x 100 t r : Light transmission, % I r : Light intensity value of spectrophotometer bath with sample I 0 : Light intensity value of spectrophotometer bath without sample 2.4. The Oxygen Permeability (OP) of the films the OP of the films was measured during 4 hours at 23±2 ºc by using systech mark gas permeability test equipment, at 170 bar O 2 of pressure (AstM, 2010). three measurements were taken from three protein films belong to each group. 2.5. Statistical analysis the resulting analysis data were evaluated by using an IbM sPss statistics 20® program. the results were given as an average ± stand- ard deviation. the one-way analysis of variance (One-Way AnOVA) was applied. In the data par- ametric assumptions for multiple comparisons occurred. the tukey test was used to locate the sources of the differences found within different groups in this test. P<0.05 variation was accept- ed as the significant discrepancy between the groups and the parameters. 3. rEsuLts the texture parameters, the light transmis- sion and the oxygen permeability values of ed- ible protein films are presented in table 1. the lowest and the highest tensile force of edible pro- tein films were 0.668±0.001 n (in the WP film), and 5.267±0.559 n (in the G film), respective- ly. the Z film had the lowest maximum elonga- tion (0.50±0.02 mm), and the EWP film had the highest maximum elongation (82.00±2.94 mm) (table 1). It was reported by sAbAtO et al. (2007) that mechanical and barrier properties of protein- based films were generally better than polysac- charide (PLs)-based films. the properties of pro- tein-based films were dependent on the various factors, such as the protein source, the pH of protein solution, the species and the amount of plasticizer, film thickness, the manufacturing conditions (temperature and relative humidity), and the structures, included film forming solu- tion (enzymes, antimicrobials, etc.) (bEnJAKuL et al., 2008). tEMIZ and YEsILsu (2006) indicated that when made from WG strong films have mechanical properties like rubber. WG films, containing a low amount of GLY, had a higher tensile resist- ance (tr) and lower elongation at break (EAb) (tAnAdA-PALMu et al., 2000). When the WG film was prepared from three different flours (com- mercial bread flour, hard red winter flour and soft white flour), it had a smooth tissue and film resistance, measured as tr, and the ratio in- creased by 50% by adding cysteine (cross-linking agent) (rAYAs et al., 1997). When the mechanical and physical properties of the WG films, plasti- cized with GLY, were examined at different tem- perature (20°c, 50°c and 80°c) and the relative humidity (35% and 70%), the tensile strength (ts) increased too, by increasing the drying tem- perature at 35% relative humidity. ts decreased, when the temperature increased, however, at 70% relative humidity. the film thickness de- creased with increasing temperature (KAYsEr- ILIOGLu et al., 2003). LIEbErMAn and GILbErt (1973) reported that the mechanical properties of edible films were considerably affected by the ratio of the plasticizer, used. the composite films can be manufactured tak- ing into account the different barriers and me- chanical properties needed by different products and thus the effectiveness of the material was in- creased. the use of the plasticizers such as GLY, polyethylene glycol (PEG), sorbitol (sOr), etc. in the film formulations or the composites is advan- table 1 - the texture parameters, the light transmission and the oxygen permeability values of edible protein films. Edible protein Tensile force Maximum elongation Light transmission Oxygen permeability film (N) (mm) (%) (mL/mm/day) SPI 2.883±0.155AF 31.85±1.11AG 20.08±0.01A 17.10±0.01A WP 0.668±0.001B 5.69±1.03B 23.35±0.01B 322.00±0.01B EWP 1.972±0.117AC 82.00±2.94C 23.22±0.01C 45.40±0.01C WG 1.275±0.147BC 57.40±2.07D 13.29±0.01D 218.00±0.01D Z 0.948±0.427BC 0.50±0.02B 19.92±0.01E 181.37±0.01E G 5.267±0.559D 35.12±1.88AF 63.30±0.01F 45.50±0.01F CL 4.145±0.198DE 68.03±1.57E 18.70±0.01G 105.10±0.01G RTP 3.559±0.720EF 39.94±0.03F 14.53±0.01H 97.10±0.01H MP 1.273±0.082BC 28.95±0.96G 39.35±0.01I 281.00±0.01I *Different letters (A, B, C) in the same column indicate the significant difference (P<0.05). Ital. J. Food Sci., vol. 27 - 2015 5 tageous to impart pliability and flexibility, which improves handling. utilization of the plasticiz- ers reduces the brittleness of film by interfering with the hydrogen bonding between the lipid and hydrocolloid molecules (tHArAnAtHAn, 2003). In the study of MArInIELLO et al. (2003), whole soy flour and apple pectin were used as raw ma- terials in order to obtain films, which due to their consistency could be perfectly handled. the films were also prepared in the presence of transglutam- inase (t-Gase). the latter films showed a smoother surface and higher homogeneity, as demonstrated by microstructural analyses, whereas studies on the mechanical properties indicated that t-Gase increased their ts and reduced their flexibility. It was reasoned that by there was a possible use of the t-Gase polymerized pectin-soy protein films as edible food or drug coatings. the proper pH value to prepare the sPI film with good mechanical and barrier properties was 10. Addition of PEG as a plasticizer at 60% of sPI weight gave better film properties com- paring with other used plasticizers. cross-link- ing of the sPI film by adding formaldehyde or glutaraldehyde at a different level into the film forming solution and the combination of sPI with the starch, also caused a noticeable im- provement in the mechanical and barrier prop- erties of the films (sOLIMAn et al., 2007). Ac- cording to dEnAVI et al. (2009), the applied dry- ing conditions when preparing the sPI film af- fected the mechanical properties, with the op- timal drying conditions of 70 ºc and 30% rela- tive humidity and 60 ºc and 60% relative hu- midity. dried under these conditions, the sPI films presented a higher ts, lower EAb val- ues. sHIH (1998) indicated that the ts and the EAb belonging to sPI was affected by pH. the mechanical properties of edible films im- proved with some of the applied methods. the mechanical properties of the cL film improved with glyceraldehyde and alcoholdiols; the ts of the cL film increased by exposing to uV beams; the ts of the Z film improved with aldehydes; the ts of the WG film developed with keratin; the ts of the WP film improved by heat treat- ment; the ts of the sPI film developed by heat treatment, uV and gamma radiation applica- tion, and by adding calcium chloride and cal- cium sulphate (McHuGH and KrOcHtA, 1994). It was expressed by GEnnAdIOs et al. (1997) that the EWP films are highly hydrophilic; they could be used for water-soluble packets (pouch- es) for ingredients in the food, chemical, and pharmaceutical industries similar to cellulose ether-based water soluble packets in commercial use. the mechanical and barrier properties of such films can be modified by varying the types and amounts of added plasticizers. When microbial t-Gase was employed as the catalyst for preparing the chitosan (cH)-oval- bumin films, the mechanical resistance of the cH-ovalbumin films increased from 24 MPa to 35 MPa. the improved mechanical and solubil- ity properties of these new materials confirmed that this enzymatic approach could be a useful tool for preparing edible films for food coating and pharmaceutical applications (dI PIErrO et al., 2007). In the study conducted by KOLOdZIE- JsKA and PIOtrOWsKA (2007), the effect of GLY on the mechanical and water barrier properties, as well as on the water solubility, of fish gelatin- cH films (4:1, w/w) cross-linked with t-Gase or 1-ethyl-3-(3-dimethylaminopropyl) carbodiim- ide (Edc) was determined. the ts of the films decreased after modification of the components with t-Gase or Edc, by about 25% and 40% re- spectively. the elongations of the enzymatical- ly modified films containing 20% of GLY and of chemically modified films containing 15% of GLY were, respectively, about 8 and 13 times higher than those of unplasticized films. However, the ts of plasticized films were, respectively, 2.5 and 5 times lower. these properties widen the practical applications of modified films as packaging ma- terial. However, the cross-linking of components with commercial preparations of t-Gase, -differ- ent to modification with Edc- increased the fra- gility of films. therefore, such films have should be plasticized. the increase in the proportion of GLY caused a reduction of the puncture force, the ts, the modulus of elasticity, and an increase of the puncture deformation and the EAb of the G film (tHOMAZInE et al., 2005). When the G film and the Z film were prepared by incorporating nisin (ns) into the film-forming solutions, the Z film with the ns of 12.000 Iu/mL had an in- crease of 11.6 MPa in the ts compared with the control, but the G film had a slight increase re- sulting from the increase of the ns concentra- tion. these results suggested that the incorpo- ration of ns into the Z film and the G film im- proved the physical properties of the films (Ku and sOnG, 2007). In the study of cArVALHO et al., (2008), the G films from the skins of nile perch, a warm-water fish species, were reported to exhibit stress and EAb similar to that of bovine bone gelatin. the gelatin, extracted from halibut skins, showed a suitable filmogenic capacity, leading to transpar- ent, weakly colored, water-soluble and highly ex- tensible films. the intermediate evaporation step at 60 ºc in the industrial procedure for drying the G film induced thermal protein degradation, caused the resulting films to be significantly less resistant and more extensible. It was seen that the G film with predominance of lower-molecu- lar-weight fractions was apparently more plasti- cized by sOr molecules, favoring a higher exten- sibility and a lower resistance in the final film. the edible films were successfully prepared from fish skin gelatin of brownstripe red snap- per (Lutjanus vitta) and bigeye snapper (Priacan- thus macracanthus). the films with the greater protein content had a higher thickness and me- 6 Ital. J. Food Sci., vol. 27 - 2015 chanical properties (ts and EAb), but lower water vapor permeability than those with the lower pro- tein content. the films without GLY were mostly brittle, and became more flexible in the presence of GLY. the ts generally decreased with increas- ing GLY concentration from 25% to 75% (JOnG- JArEOnrAK et al., 2006). IWAtA et al. (2000) ex- pressed that edible films prepared from water- soluble fish proteins, had better flexibility com- pared to most of the other protein films. the pH change, the various physical and chemical treat- ments and the properties of plasticizer affected the quality of fish protein film. Lower mechanical properties were found in the films prepared from the lower quality washed fish mince (bEnJAKuL et al., 2008). the ts of the films was higher, when prepared at acidic (pH 2, 3) and alkaline (pH 11, 12) conditions. the film with the lowest ts was made at pH 7. the mechanical resistance of the myofibrillar protein (MYFP) based films were sub- stantially lower than the synthetic films -such as polypropylene (PP), polyethylene and poly- vinyl dichloride- but was relatively close to low density polyethylene (LdPE) (sHIKu et al., 2003). GLY and PEG plasticizers gave flexible structure to the films prepared from water soluble fish pro- tein. As the concentration of GLY increased, ts decreased with the concomitant increase of EAb. In contrast, PEG showed more marked influence on ts than on EAb. GLY:PEG ratio of 2:1 exhib- ited the maximum EAb value. It was confirmed that MYFP based films plasticized with the mix- ture of GLY-PEG showed lower ts (2.5-3.0 MPa) than with only GLY (5.0 MPa) or with only PEG plasticized films (7.0 MPa) (tAnAKA et al., 2001). PArrIs and cOFFIn (1997) observed that Z- based films plasticized with a mixture of GLY- polypropylene glycol (PPG) showed lower ts and lower elastic modulus than with only GLY plas- ticized films or PPG plasticized films. Moreover, the films plasticized with the mixture of GLY-PEG caused higher EAb (117.8%) than those with only GLY (2.6%) or PEG plasticized films (2.8%). the functional properties of the fish protein films produced by the thermo-melting tech- niques were similar to known protein films and the ts of the films were similar to LdPE (cuQ et al., 1998). the films obtained from tilapia fish treated at 65°c/30 minutes were more re- sistant and more rigid than the films treated at 40°c/30 minutes (GArcIA and sObrAL, 2005). When the protein concentration was treated at 90°c/30 minutes, the filmogenic solution was 2 g of sarcoplasmic protein (srcP)-MYFP/100 g filmogenic solution, the prepared films were more resistant than the respective films (sO- brAL et al., 2005). cuQ et al. (1995) expressed that MYFP films produced from sardine had the higher tr than that obtained from other protein films, such as Z, WG, sPI and WP. the quality of Alaska pollack surimi (srM) films was decreased in order to determine the influence of the srM quality on the ts, and the EAb val- ues. thawed Alaska pollack srM was incubat- ed at 30ºc for 20 minutes (slight protein dena- turation) and at 30 ºc for 5 hours (complete pro- tein denaturation) in order to decrease the srM quality. slight protein denaturation caused a de- crease in the EAb of the films and complete de- naturation gave rise to a reduction of the ts, and the EAb values (sHIKu et al., 2004). MYFP-based films were developed from a film-forming solution based on fish mince and the influence of plasticiz- ers on the protein film quality was investigated. When no plasticizer was introduced in formula- tion the films were relatively brittle and needed to be handled very carefully, and GLY, sOr and su- crose were added in various concentrations. Plas- ticization of the MYFP-based films induced a large decrease in film strength and elasticity and an in- crease in deformation properties (cuQ et al., 1997). sOr plasticized films were the most brittle, with the highest ts (3.14 MPa). In contrast, GLY and PEG plasticized films exhibited flexible structure, despite the low ts (2.13 MPa and 1.80 MPa, re- spectively). As plasticizer concentration increased, the ts decreased concomitant with an increase in EAb (bOurtOOM et al., 2006). Propylene glycol alginate (PGAL) was incorpo- rated into Alaska pollack srM film in order to im- prove their mechanical properties. the ts of the PGAL-srM films prepared at pH 11 were twice as high compared to the srM films prepared at pH 7. the EAb was not affected by the incorporation of PGAL. results revealed that the formation of cross-linkages between epsilon-amino groups of lysine residues in srM proteins and mannuronic acid esters of PGAL above pH 10 was responsi- ble for the increased ts of the films (WEnG et al., 2006). the effect on the ratios of MYFP to srcP from round scad (Decapterus maruadsi) muscle on the properties of the resulting films was in- vestigated. the ts of the films decreased with an increased srcP content. the films prepared from MYFP:srcP ratio of 10:0 (w/w) exhibited the highest ts. the EAb of the films, prepared with srcP content greater than 30%, had the decreased EAb (ArtHAn et al., 2008). A comparison could not be made, due to no mention in the literature to studies involving similar textural values of edible protein films obtained from the texture analyzer equipment used in our study. Moreover, when both tensile test parameters were evaluated, as seen clearly in Fig. 1 and Fig. 2, placing the cL film in the second range, this film group outclassed other film groups considerably. sArIKus (2006) ex- pressed that the cL film is used in sausage coat- ing more than natural coatings. the most im- portant advantages of these films are that they remain strong in producting process conditions, having a flexible structure with a high-tensility. the G protein film obtained the highest Lt val- ue (63.30%±0.01); the WG protein film obtained, however, the lowest Lt value (13.29%±0.01) (ta- ble 1). Ital. J. Food Sci., vol. 27 - 2015 7 because food products are exposed to light trig- ger oxidative reactions, the products were packed with non-light transmitting packaging material in order to protect them from the light. there are a limited number of studies mentioned in the liter- ature about the Lt value of edible films. sHIKu et al. (2003) expressed that MYFP films, prepared from blue marlin flesh, have excellent barrier properties to uV light in the range of 200-280 nm regardless of pH. However, the uV barrier property of the films gradually became poor above the wavelength of 300 nm. In con- trast, the MYFP film prepared at pH 7 blocked the most light in the uV-visible range from 350 to 800 nm because of its semi-transparency. In our study, the Lt of the WG film was meas- ured as the lowest value (13.29%±0.01) at 560 nm/23±2 ºc. the rtP film possessed the second lowest Lt value after the WG film (Fig. 3). com- parisons could not be made, as there are no sim- Fig. 1 -the changes of the tensile force val- ues of edible protein films. Fig. 2 -the changes of the maximum elon- gation values of edible protein films. ilar studies in the research literature of Lt meas- urements conducted at the same wavelength as in our study. However, it is possible to say that the WG film can be more effective protecting prod- ucts from light than other protein films. the highest OP value was observed at 322.00±0.01 mL/mm/day in the WP film, and the lowest OP value was observed at 17.10±0.01 mL/mm/day in the sPI film (Fig. 4). the OP value of the EWP film and the OP value of the G film; the OP value of the cL film and the OP value of the rtP film was determined to be close to each other in. the diffusion of gas and water vapor into film is called transition. these gases and the water vapor were absorbed by a surface of the polymer and oscillated by the other surface of the poly- mer during transition. the films have different barrier properties according to component prop- erties and manufacturing techniques. the polar polymers, such as protein and carbonhydrates, 8 Ital. J. Food Sci., vol. 27 - 2015 show low gas permeability and high water vapor permeability. In contrast, whilst materials (con- taining apolar hydrocarbon such as lipid) con- stitute an excellent barrier against the water va- por transition, they are not an effective barrier to gas transition. the chemical structure and the shape of the transition or absorbed film matrix substance is effective at the speed of diffusion and transfer. For example, the small molecules diffuse faster than the big molecules or the po- lar molecules diffuse faster than the apolar mol- ecules in the polar films (cAGrI-MEHMEtOGLu, 2010). the rate of rancidity, causing lipid oxi- dation and brown coloration, as well as causing myoglobin oxidation in meats, could be reduced by using edible coatings with the low OP (GEn- nAdIOs et al., 1997). It was implied by YILMAZ et al. (2007) that WP-based edible film and coating slowed gas (O 2 , cO 2 ) transfer. the OP of the cL Fig. 3 -the chang- es of the light transmission val- ues of edible pro- tein films. Fig. 4 -the chang- es of the oxygen permeability val- ues of edible pro- tein films. film was <0.04 cm3.μm/m2.dk.Pa; the OP of the Z film was 11.8 cm3.μm/m2.dk.Pa; the OP of the WG film was 3.9-6.1 cm3.μm/m2.dk.Pa; the OP of the sPI film was 1.6-4.5 cm3.μm/m2.dk.Pa; and the OP of the WP film was 18.5-76.1 cm3. μm/m2.dk.Pa (LIEbErMAn and GILbErt, 1973). LIn and ZHAO (2007) expressed that the O 2 per- meability (7.84x10-19 m3.m/m2.s.Pa) of the Z- based coating was lower than the O 2 permeabil- ity of plastic films (such as LdPE, PP, polysty- rene and polyvinylchloride) and of PLs, PLs/lipid composite coatings, but higher than the O 2 per- meability (2.89x10-17 m3.m/m2.s.Pa) of WG coat- ings. It was observed that the O 2 permeability of the WG coating was close to the O 2 permeability (2.25x10-17 m3.m/m2.s.Pa) of LdPE. It was rec- ognized in literature that the OP of edible films was affected considerably by factors such as the preparation conditions (temperature and relative Ital. J. Food Sci., vol. 27 - 2015 9 humidity); the type and the amount of plasticiz- ers, the incorporation of various chemicals; heat- treatments and pH levels. For example, McHuGH and KrOcHtA (1994) specified that the gas per- meability of the cL film decreased with formal- dehyde and chrome tannic acid, whilst the OP of the WP film and the sPI film improved with heat treatment. the OP (3.16 cm3.μm/m2.dk.Pa- at 23 ºc and 50% relative humidity) of the WG film, made with 40% GLY, was found to be sim- ilar to the OP (3.82 cm3.μm/m2.dk.Pa-at 23 ºc and %0 relative humidity) of the film obtained by GEnnAdIOs et al. (2006) (MuJIcA-PAZ and GOntArd, 1997). despite the fact that the OP of all WG films was low, the OP level could be raised by increasing the GLY concentration. It was seen that temperature has less effect on OP than the relative humidity. the low OP of the WG films may be due to their polar nature and line- ar structure, leading to the high cohesive-ener- gy density and the low free volume (tAnAdA-PAL- Mu et al., 2000). sHIH (1998) expressed that the OP of the WG film decreased by adding of miner- al oil and dipping in ca+2. It was specified that the sPI coatings were effective oxygen barriers (OP; 3.14x10-19 m3.m/m2.s.Pa) at low relative hu- midity conditions, especially as their high oxy- gen barrier properties made them suited to gave the facility their applications such as flavour and pharmaceutical microencapsulated agents or as coatings for fruit, vegetable and cheese. It was reported that the WP-based films also had ex- cellent oxygen barrier properties (OP; 1.13x10-18 m3.m/m2.s.Pa) at low and medium relative hu- midity when they compared with synthetic poly- mers (LIEbErMAn and GILbErt, 1973). the prop- er pH value for the preparation of sPI film with good barrier properties was 10; the O 2 permea- bility of the sPI film was 1.06 cm3.μm/m2.dk.Pa at this pH value. the addition of PEG as a plas- ticizer at 60% of sPI weight made the film prop- erties better, compared with other plasticizers, and the O 2 permeability of the sPI film was 0.76 cm3.μm/m2.dk.Pa. the cross-linking of the sPI film by adding formaldehyde or glutaraldehyde at different levels into the film forming solution improved the barrier properties of the result- ing films (sOLIMAn et al., 2007). dEnAVI et al. (2009) found that the applied drying conditions used in sPI film manufacturing affected the bar- rier properties of the film: the O 2 permeability of the film was 18.2 cm3.μm/m2.dk.Pa dried at 70 ºc and 30% relative humidity and the O 2 per- meability of the film was 47.6 cm3.μm/m2.dk.Pa dried at 60 ºc and 60% relative humidity. In our study, the sPI film had the lowest O 2 permeabili- ty (17.10±0.01 ml/mm/day) (table 1). the prop- erties of sPI film can be improved with applica- tion of additional methods in light of the litera- ture (LIEbErMAn and GILbErt, 1973; sOLIMAn et al., 2007; dEnAVI et al., 2009) and it can be used for the purpose of protecting food products from the harmful effect of oxygen. 4. cOncLusIOns In our study of the mechanical properties of edible protein films, both tensile test param- eters (tensile force and maximum elongation) were evaluated, placing of the cL film in the second range: this film group outclassed other film groups considerably. It was observed that the WG film possessed the lowest Lt value. It is possible to say that the WG film is more ef- fective in protecting products from light than other protein films. the lowest OP in our study belonged to the sPI film. the properties of the sPI film -which can be improved with addition- al methods in light of the literature- can be used for the purpose of protecting food prod- ucts from the harmful effect of oxygen. AbbrEVIAtIOns cH: chitosan PGAL: Propylene glycol alginate cL: collagen PLs: Polysaccharide EAb: Elongation at break PP: Polypropylene EdK: 1-ethyl-3-(3-dimethylaminopropyl) carbodiimid PPG: Polypropylene glycol EWP: Egg white powder protein rtP: rainbow trout protein G: Gelatin sOr: sorbitol GLY: Glycerol sPI: soy protein isolates LdPE: Low density polyethylene srcP: sarcoplasmic protein Lt: Light transmission srM: surimi MP: Mackerel protein t-Gase: transglutaminase MYFP: Myofibrillar protein tr: tensile resistance naOH: sodium hydroxide ts: tensile strength ns: nisin WG: Wheat Gluten OP: Oxygen permeability WP: Whey protein PEG: Polyethylene glycol Z: Zein AcKnOWLEdGEMEnts this work was supported by the research Fund of Istanbul university, Project number-3669. rEFErEncEs Artharn A., benjakul s. and Prodpran t. 2008. the effect of myofibrillar/sarcoplasmic protein ratios on the properties of round scad muscle protein based film. Eur. Food res. technol. 227 (1): 215-222. 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Elek. der. 1: 59-64. Paper Received December 18, 2013 Accepted May 28, 2014