CHAPTER 2 REVIEW OF LITERATURE

Transcription

1 CHAPTER 2 REVIEW OF LITERATURE This chapter deals with the scientific work carried out by researchers in developing the edible film/coating, their properties and in turn enhancing the value, quality and shelf life of foods in general and of fruits and vegetables in particular. The chapter is divided into 4 sections namely 2.1 Formulation of edible film 2.2 Properties of edible film 2.3 Preservation of food by using edible coating/film 2.4 Edible film as means of fortification. 2.1 Formulation of Edible Film Edible films can be prepared from various biobased materials like carbohydrates, proteins, fat and waxes and combination thereof. The properties of film are modified with addition of compounds like plasticizers and cross linking agents. The edible films designed for a particular food must be compatible with the product and also meet the requirements of that product. The current topic is divided into three sub topics namely Protein based edible films Carbohydrate based edible films Composite edible films Protein Based Edible Films The protein as a source of edible films provides very good mechanical properties like tensile strength, elongation at break and modulus of elasticity but the problem with protein based films is that they are poor water vapour and gas barrier properties. The research work associated with protein based edible film is as summarized below. 11

2 Piermaria et al, (2011) evaluated the ability of kefiran to form films and the effect of glycerol addition at different concentrations on film properties. Kefiran was able to form films at concentrations ranging from 5 to 10 g/kg. The concentration 10 g/kg was selected because the films were easily removed from the plate. These films exhibited good water vapor barrier properties and the addition of 25 g of glycerol per 100 g of polysaccharide allowed the optimum value of 4.09 X g/m s Pa to be obtained. Films without glycerol were brittle and rigid since they showed high Young s modulus and tensile strength values and low deformation at break. Glycerol addition led to extremely high elongation values, allowing flexibilities comparable to those of synthetic materials. Denavi et al, (2009) investigated the influence of drying conditions on edible films prepared from commercial soy protein isolate (CSPI) and laboratory prepared soy protein isolate (LSPI) The films were dried in a chamber with air circulation under controlled conditions of relative humidity (24, 30, 45, 60, 66 percent) and air temperature (34, 40, 55, 70, 76 ºC). It was found that mechanical properties of films made from LSPI and CSPI are influenced in a very different way by the drying conditions due to a diverse initial protein conformation in both materials Mastromatteo et al, (2008) investigated the individual and interactive effects of the spelt and wheat bran as well as glycerol, on the properties of wheat gluten based edible films. Results highlight that the glycerol presence had a negative effect on water vapor permeability (WVP) values of the films (increase of WVP), whereas the bran presence had a positive influence (decrease of WVP). The Young s Modulus of the composite films increased with the increase of bran concentration and with the decrease of glycerol. Cho et al, (2007) prepared edible films from membrane processed soy protein concentrate at various film forming solution phs. Their mechanical, barrier, and physical properties were 12

3 compared with soy protein isolate films. As the film solution ph increased from 7 to 10, the resulted MSC films were more transparent, yellowish, and had lower oxygen permeability. However, tensile strength, Young s modulus and water vapor permeability of MSC films were not affected by film solution phs. Bamdad et al, (2006) prepared edible film from lentil protein concentrate (LPC) by using LPC (5 g/100 ml water) and glycerin (50 percent, w/w of LPC). Water Vapour Permeability values and other characteristics of the lentil protein-based edible films were comparable with other edible protein films. LPC film had more red and less yellow color; it was also observed that the film had good mechanical properties and water vapor permeability together with good solubility. Taylor et al, (2005) examined several food compatible solvents to replace aqueous ethanol, commonly used for prolamin film casting. Glacial acetic acid and lactic acid were identified as the best primary solvents and 55 percent (w/w) aqueous isopropanol as a good binary solvent. The sensory, tensile, and water barrier properties of the films cast from glacial acetic acid at 25 0 C and aqueous ethanol at 70 0 C were almost the same. However, the use of glacial acetic acid at 25 0 C for casting kafirin films is advantageous as it gave films of more consistent quality. Vanin et al, (2005) studied the effect of plasticizers and their concentrations on the thermal and functional properties of gelatinbased films. Four polyols (glycerol GLY, propylene glycol PPG, di- DTG and ethylene glycol ETG) were used in five concentrations: 10, 15, 20, 25, and 30 g plasticizer/100 g of gelatin to prepare the film. Plasticizer effect and efficiency were observed with DTG and ETG on the thermal properties, and with the GLY in terms of functional properties. de Carvalho and Grosso (2004) found that protein films possess good gas barrier properties at low to intermediate relative humidity but reduced water vapor barrier properties, which limits 13

4 their application. The introduction of chemical or enzymatic modifications could be an alternative to improve the cohesion properties of the polymeric matrix due to the formation of crosslinkages, thus improving the barrier characteristics and the mechanical resistance and decreasing the film solubility. Hernandez-Munoz et al, (2004) studied the effect of crosslinking agents glutaraldehyde (GTA), glyoxal (GLY) and formaldehyde (FA) on relevant properties of films based on a glutenin-rich fraction from commercial wheat gluten. The gliadin-rich fraction was separated from glutenin-rich fraction using 70 percent (v/v) aqueous ethanol solution. The 70 percent ethanol-insoluble fraction (glutenin-rich fraction) was dispersed in 50 percent (v/v) aqueous ethanol at 40 0 C and ph 5. GTA, GLY or FA was added in concentrations of 2, 4 and 8 percent (g/100 g dry protein) to the film-forming solution. Films were cast and dried at 23 0 C and 40 percent relative humidity (RH) for 10 h. Water vapour permeability values decreased by around 30% when FA, GTA or GLY were incorporated. The highest tensile strength values were obtained using FA, followed by GTA and GLY. Glass transition temperature of cross-linked films shifts to slightly higher values when cross-linking agents were used. Films treated with GTA and GLY were darker with a yellowish color. Addition of concentrations up to 2% of cross-linker did not modify the properties of the films. Water sorption behavior of control and cross-linked films did not differ. Gennadios et al, (1993) evaluated the effect of ph of film forming solution of Soy protein isolate (SPI) and wheat gluten (WG) films. They observed that WG films formed within ph 2-4 and 9-13, whereas SPI films formed within ph 1-3 and Film formation was inhibited by poor protein dispersion around the isoelectric ph region of SPI (ph 4.5) and WG (ph 7.6). Film formation was inhibited by poor protein dispersion around the isoelectric ph region of SPI (ph 4.5) and WG (ph 7.6). SPI films prepared from ph 6 to 11 had significantly higher TS, higher E, and lower WVP than films from ph 1 to 3. WG 14

5 films produced under alkaline conditions had significantly higher TS than films processed under acidic conditions. The research related to formulation of protein based edible film is summarized in Table Carbohydrate Based Edible Films Bourtoom and Chinnan (2008) developed biodegradable blend films from rice starch chitosan by casting film-solution on leveled trays. The influence of the ratio of starch and chitosan (2:1, 1.5:1, 1:1, and 0.5:1) on the mechanical properties, water barrier properties, and miscibility of biodegradable blend films was investigated. The biodegradable blend film from rice starch chitosan showed an increase in tensile strength (TS), water vapor permeability (WVP), lighter color and yellowness and a decreasing elongation at the break (E ), and film solubility (FS) after incorporation of chitosan. However, the WVP of rice starch chitosan biodegradable film was characterized by relatively lower WVP than chitosan films but higher than polyolefin. Fadnis et al, (2008) studied the miscibility of Hydroxy propyl methyl cellulose (HPMC)/polyvinyl alcohol (PVA) blends edible polymer films. It was revealed that HPMC/PVA blend is miscible when the HPMC content is more than 60 percent in the blend at 30 and 50 0 C and also that the change in temperature in the range of experiment has no significant effect on the miscibility of HPMC/PVA polymer blend. Pinotti et al, (2007) analyzed the effect of an electrical field applied during drying on microstructure and macroscopic properties of films obtained with different mixtures of chitosan (CH) and methyl cellulose (MC). CH treated films showed higher Young s Modulus values than the control ones; in composite control samples, YM and tensile strength increased with CH concentration, leading to stronger films. 15

6 Table 2.1 Review on Formulation of Protein Based Edible Films Sr Author Year Important finding No. 1 Piermaria et al 2011 Edible films can be obtained from kefirin by using glycerol as plasticizer 2 Denavi et al 2009 Drying conditions like RH and air temperature affects on mechanical properties of film. 3 Mastromatteo et al 2008 Addition of bran positively affects the WVP value whereas glycerol has negative effect. 4 Cho et al 2007 Various properties of edible film from soy protein isolate and membrane processed soy protein concentrate were compared 5 Bamdad et al 2006 Edible films can be prepared from lentil protein concentrate and their properties are comparable with other protein films. 6 Taylor et al 2005 Aqueous ethanol can be replaced by several food compatible solvents like glacial acetic acid and lactic acid for prolamine film casting. 7 Vanin et al 2005 Different plasticizers affect on thermal and functional properties of gelatin based edible film. 8 de Carvalho and Grosso 2004 Water vapor barrier properties of protein films can be improved through chemical or enzymatic modifications. 9 Hernandez- Munoz 2004 Different cross linking agents have their effect on properties of wheat gluten film. 10 Gennadios et al 1993 Wheat gluten and soy protein isolate films requires different ph values for film formation. 16

7 Muller et al, (2008) investigated the effects of plasticizer namely glycerol and sorbitol on the water sorption isotherms and water vapor permeability (WVP) of cassava starch films prepared by casting. The WVP values were determined in three ranges of RH, (2 33 percent, percent and percent). In all cases, an increase in WVP values was observed with increasing plasticizer concentration and RH. Paes et al, (2008) investigated the effect of the paste preparation conditions on the properties of cassava starch paste and its films. The films were prepared by casting starch pastes gelatinized under eight different conditions: 70, 80, 90 or C at high (18,000 rpm) and low shear rate (150 rpm). It was shown that the use of a high shear affected all mechanical properties determined by tensile tests, which were lower for all temperatures compared to the films prepared using low shear rate. Alves et al, (2007) produced cassava starch films by casting. The effects of different amylose quantities (6.3, 15.6 and 25.0 g/100 g of starch) and glycerol contents (20.0, 32.5 and 45.0 g/100 g of starch) on filmogenic solution were evaluated. The enrichment of filmogenic solutions with amylose solution originates stronger and more permeable films. Glycerol behaved as a typical plasticizer in starch films; with increasing glycerol concentration, WVP, strain at break and puncture deformation increased, and elongation at break, YM and puncture strength decreased. Tapia-Blacido et al, (2005) studied the filmogenic capacity of amaranth flour films were obtained by casting process using glycerol as plasticizer. The biofilms presented a yellowish color, moderate clarity, and high flexibility but low tensile strength. Nevertheless they showed less oxygen and water permeability than other protein and polysaccharide films. The review of literature related to formulation of carbohydrate based film can be summarized as shown in Table

8 Table 2.2 Review on Formulation of Carbohydrate Based Films. Sr Author Year Important finding No. 1 Bourtoom and Chinnan 2008 The biodegradable blend film prepared from rice starch and chitosan shows increase in tensile strength and water vapour permeability and decrease in elongation at break and solubility after incorporation of chitosan. 2 Fadnis et 2008 Hydroxyl propyl methyl cellulose al /polyvinyl alcohol blend is miscible when HPMC content is more than 60 per cent at 30 and 50 0 C 3 Pinotti et al 2007 Chitosan treated films showed higher Young s Modulus values than the control ones; in composite control samples, Young s Modulus and tensile strength increased with chitosan concentration, leading to stronger films. 4 Muller et 2008 The WVP values of Cassava starch al edible films are increases with increase in plasticizer concentration and RH. 5 Paes et al 2008 In case of cassava starch films the high shear rates affect all mechanical properties. 6 Alves et al 2007 The enrichment of cassava starch film with amylose increases strength and permeability of film. 7 Tapio- Blacido et al 2005 Amaranth flour with glycerol gives films with high flexibility but low tensile strength, oxygen and water vapor permeability 18

9 2.1.3 Composite Edible Films Vargas et al, (2008) prepared edible films based on high molecular weight chitosan (CH) and different concentrations of oleic acid (OA). Results showed that higher the OA content, the lower the WVP and the moisture sorption capacity. In general, the addition of OA into the CH matrix leads to significant increase in gloss and translucency and decrease in the tensile strength, elongation at break and Young s modulus of the composite films. The mechanical and optical properties of the films were related with their microstructure, which was observed by Scanning Electron Microscope. Gounga et al, (2007) prepared edible films from whey protein isolate (WPI), five percent, seven percent and nine percent (w/v) WPI were used at three WPI:Gly ratios (3.6:1; 3:1; and 2:1). Five percent WPI with a 3.6:1 WPI:Gly ratio showed the best combination with factors considered being thickness and water vapor permeability (WVP), while the nine percent WPI with 3.6:1 WPI:Gly showed the best result as seen from the oxygen permeability (OP). Further studies were conducted by adding pullulan (PUL) at different WPI:PUL ratios (1:0; 1:1; 2:1; 3:1; 4:1; 5:1; 6:1; 8:1; 10:1) to the selected film. WPI PUL film had a good appearance and 1:1 WPI: PUL resulted in films with greatest values of OP, WVP and transmittance. Bertan et al, (2005) found that composite edible/degradable films produced with hydrocolloids and lipids can result in better functionality than films produced with the components, especially with respect to their barrier properties. Of the lipids, waxes produce the best water vapor barrier properties, but produce fragile/brittle films. Films with the addition of acids, and the blend with elemi presented better water vapor barrier properties as compared to the gelatin/triacetin film. The mechanical resistance decrease with the addition of the lipids. However the opacity and soluble matter increased. 19

10 Xu et al, (2005) prepared chitosan/starch composite films by combining chitosan (deacetylated degree, 90 percent) solution and two thermally gelatinized corn starches (waxy starch and regular starch with 25 percent amylase). Regardless of starch type, both the Tensile Strength (TS) and Percent Elongation (E) of the composite films first increased and then decreased with starch addition. Composite film made with regular starch showed higher TS and E than those with waxy starch. The addition of starch decreased WVTRs of the composite films Yu et al, (2004) investigated the effect of carboxymethyl cellulose on the aggregation of formulation based on calcium caseinate, commercial whey protein, and a 1:1 mixture of soy protein isolate and whey protein isolate. The aggregation behavior was enhanced by means of physical treatments, such as heating at 90 0 C for 30 min or gamma-irradiation at 32 kgy. A synergy resulted from the combination of CMC to gamma-irradiation in Caseinate/CMC and SPI/WPI/CMC formulations. Ryu et al, (2002) prepared the edible composite films using high-amylose corn starch (HACS) and corn zein. HACS was gelatinized using the specially designed high-pressure container. The HACS film containing 20 g sorbitol/100 g as a plasticizer had suitable physical properties. The HACS film coated with corn zein containing 20 g oleic acid/100 g had moderate physical properties and barrier properties. Chen and Nussinovitch (2000) introduced xanthan gum into a traditional, wax-based coating formulation for easy peelers. The xanthan created disturbances in the ordered, regular structure of the traditional wax coating, as observed by electron microscopy. In addition, less off-flavors were detected by sensory evaluation of juice extracted from the fruit coated with the wax xanthan coating Arvanitoyannis et al, (1998) prepared films of chitosan and gelatin by casting their aqueous solutions (ph < 4.0) at 60 0 C and evaporating at 22 or 60 0 C (low- and high-temperature methods, 20

11 respectively) and plasticized with water or polyols. They found that an increase in the total plasticizer content resulted in a considerable decrease of Young s modulus and tensile strength (up to 50 percent of the original values when 30 percent plasticizer was added), whereas the percentage elongation increased (up to 150 percent compared to the original values). Rhim et al, (1998) determined the effect of dialdehyde starch (DAS) on selected physical properties of cast soy protein isolate (SPI) films. Films were cast from heated (70 C for 20 min) alkaline (ph 10) aqueous solutions of SPI at 5 g: 100 ml water, glycerin (50 percent, w: w, of SPI), and DAS at 0, 5, 10, 15, or 20 percent (w: w) of SPI. The DAS addition increased film yellowness suggesting occurrence of cross-linking between SPI and DAS. The films with 5 or 10 percent DAS had increased TS compared to control films, whereas film E was not significantly affected by DAS. Small increases in WVP and MC were observed for DAS containing films. Shih (1996) prepared edible films using a combination of rice protein concentrate and the polysaccharide pullulan and observed that the protein-pullulan mixture with up to 50 percent protein concentrate could be cast on a glass plate. into films with tensile strength of about 18 MPa and water vapor permeability of 40 g x mil/m 2 x day x mmhg. Film strength and water vapor resistance were improved by the addition of small amounts of propylene glycol alginate under alkaline condition. Oils were also incorporated into the film for improved water vapor resistance. The review of literature related to formulation of composite edible film can be summarized as shown in Table

12 Sr No. Table 2.3 Review on Formulation of Composite Edible Films Author Year Important finding 1 Vargas et al 2008 In chitosan oleic acid composite film increased amount of oleic acid increases gloss and translucency while decreases WVP, tensile strength and elongation at break. 2 Gounga et al 2007 Optimization of concentration of whey protein isolate, glycerol and pullulan. 3 Bertana et al 2005 Edible films produced with hydrocolloids and lipid can result in better functionality than films produced with individual components. 4 Xu et al 2005 In chitosan starch composite films comosition and type of starch used affects on properties of edible film. 5 Yu et al 2004 Composite edible film from carboxymethyl cellulose, whey protein isolate, soy protein isolate and calcium caseinate the aggregation behavior can be modified by treatments like heating and gamma irradiation. 6 Ryu et al 2002 The high amylase corn strach film coated with corn zein containing 20 g oleic acid/100 g had moderate physical properties and barrier properties. 7 Chen and Nussinovitch 8 Arvanitoyannis et al 2000 Xanthan gum creates disturbance in ordered, regular structure of traditional wax coating In chitosan gelatin film increase in total plasticizer content decreases Young s modulus and tensile strength while percent elongation increases. 9 Rhim et al 1998 Addition of dialdehyde starch to soy protein isolate film increases yellowness, tensile strength and WVP values. 10 Shih 1996 Satisfactory edible film can be obtained from rice protein concentrate and pullulan 22

13 2.2 Properties of Edible Film Edible films are biodegradable, able to act as moisture, gas, aroma and lipid barriers. Various natural materials like polysaccharides, lipids and proteins have been used to prepare edible films. The properties of edible films have been reported to be affected considerably by different factors at different stages of the process, like a) nature and composition of biopolymers b) nature of plasticizers and degree of plasticization, c) Presence of functional additives(cross linking agents), d) processing parameters (temperature, ph, nature of mixing, drying etc). The overall properties of edible films studied are grouped into following three subcategories Barrier properties Mechanical properties Barrier Properties Ghanbarzadeh et al, (2007) prepared zein based edible films by using sugars (fructose, galactose and glucose) as plasticizers. They found that the pure zein film had high WVP and adding of sugars to 0.7 g/g zein led to decrease of WVP. The films containing galactose had the lowest WVP. Sothornvit and Pitak (2007) investigated the effect of banana flour, glycerol (Gly) and pectin content on film oxygen permeability (OP) and mechanical properties of banana films. Banana flour content significantly affected film OP; whereas, Gly and pectin contents did not significantly affect film OP. Srinivasa et al, (2007) prepared chitosan films by blending with polyols (glycerol, sorbitol and polyethylene glycol (PEG)) and fatty acids (stearic and palmitic acids). The glycerol blend films showed decrease, whereas sorbitol and PEG blend films showed increase in the water vapor permeability (WVP) values. No considerable differences in WVP were observed in fatty acid blend films. 23

14 Mali et al, (2006) prepared edible film from corn, cassava and yam starch with glycerol as plasticizer and observed that unplasticized films showed water vapor permeability (WVP) values ranged from 6.75 to 8.33 x g m -1 s -1 Pa -1. These values decrease when glycerol content reached at 20 g/100 g starch because a more compact structure was formed and, then, at 40 g glycerol/100 g starch,wvp increased because film matrixes became less dense. Prodpran and Benjakul (2005) studied the effect of acid and alkaline solubilizing processes on the properties of the protein based film from surimi. Film with alkaline process had slightly lower water vapor permeability (WVP), compared to that prepared by acid solubilizing process. Increase in protein concentration resulted in an increase in WVP. Ayranci and Tunc (2003) examined the effects of the presence of stearic acid (SA), ascorbic acid (AA) and citric acid (CA), in varying amounts in the film composition, on the oxygen permeability (OP) of methyl cellulose based edible films. The OP increased with increasing SA content of the film and decreased with the inclusion of AA or CA in the film composition. Paramawati et al, (2003) prepared zein based edible films plasticized individually with 20 percent lauric acid; octanoic acid; triethylene glycol; polyethylene glycol, or lactic acid. Both octanoic acid and lactic acid did not affect on water vapor and oxygen permeability (WVP and OP). Lauric acid exhibited improved WVP and OP values. On the other hand triethylene glycol and polyethylene glycol did not affect the existing good performance of barrier properties of films Gaudin et al, (2000) found that sorbitol had an antiplasticisation effect for contents below 21 percent (wt percent), as indicated by a ten-fold drop in oxygen permeability of starch based film. It was 1.43 x cm 3 cm/cm 2 s Pa for the sample not containing sorbitol and 0.15 x cm 3 cm/cm 2 s Pa for the sample 24

15 containing 8.8 percent of sorbitol. For sorbitol contents above 21 percent (wt percent), oxygen permeability increased slightly. Yang and Paulson (2000) incorporated bees wax or a 1:1 blend of stearic-palmitic acids (S-P) into gellan films through emulsifcation to form gellan/ lipid composite films. Addition of the lipids to gellan films significantly improved the WVP. Bees wax was more effective than S-P acids in reducing the WVP Banerjee and Chen (1995) compared the functional properties of whey protein concentrate films with those of the films derived from sodium caseinate, potassium caseinate, calcium caseinate, and whey protein isolate. Water vapor permeability of simple whey protein concentrate film was lower than that for films of sodium caseinate, potassium caseinate, and whey protein isolate. Composite whey protein concentrate film had the lowest water vapor permeability of all the milk protein films. Park and Chinnan (1995) made edible films from proteins (corn-zein and wheat gluten) and celluloses (methyl cellulose and hydroxypropyl cellulose), and tested for permeability of gases. Oxygen and carbon dioxide permeabilities of edible films were generally lower than those of plastic films. However, water vapor permeabilities of edible films were higher than those of plastic films. The concentration of plasticizer significantly affected the permeability of gases. The gas permeabilities, O2, CO2 and water vapor, of cellulose films increased as the concentration of plasticizer increased. Addition of lipid in the hydroxypropyl cellulose (HPC) film decreased the gas permeability linear relationships were found between permeability of gases and film thickness in protein films. The research related to study of barrier properties of film can be summarized as shown in Table

16 Table 2.4 Review on Barrier Properties of Edible Film Sr Author Year Important finding No. 1 Ghanbarzadeh et al 2007 WVP values of zein films can be lowered by addition of sugars 2 Sothornvit and 2007 In a composite edible film banana Pitak flour affects film oxygen permeability whereas glycerol and pectin does not affect significantly 3 Srinivasa et al 2007 Glycerol as plasticizer in chitosan film decreases WVP values while sorbitol and polyethylene glycol increases it. 4 Mali et al 2006 The WVP values of a edible film from corn, cassava and yam starch initially decreases with increase in amount of plasticizer and then it increases. 5 Prodpran and 2005 Acidic or alkaline solublizing Benjakul process affects on barrier properties of surimi protein film 6 Ayranci and 2003 Methyl cellulose based edible films Tunc shows increase in oxygen permeability with increasing stearic acid content while ascorbic acid and citric acid found to decrease it. 7 Paramawati et al 2003 In case of Zein films octanoic acid, lactic acid Lauric acid triethylene glycol and polyethylene glycol as a plasticizer exhibited different effects on WVP and OP values. 26

17 8 Gaudin et al 2000 In starch based edible film sorbitol has antiplasticization effect below 21 percent level decreasing the oxygen permeability values and above this level oxygen permeability increased slightly. 9 Yang and Paulson 2000 Addition of lipids to gellan films significantly improves the WVP 10 Banejee and Chen 1995 Water vapor permeability of simple whey protein concentrate film was lower than that for films of sodium caseinate, potassium caseinate, and whey protein isolate. 11 Park and 1995 Oxygen and carbon dioxide Chinnan permeability of edible films are generally lower, however water vapour permeability is film is higher than those of plastic films, Mechanical Properties Fabra et al, (2008) optimize film composition in terms of kind and ratio of plasticizer (glycerol and sorbitol) and lipids (oleic acid and bees wax) for sodium caseinate based films. The glycerol was more effective as plasticizer than sorbitol in the caseinate matrices; films with 90 percent sorbitol had similar tensile properties to those elaborated with percent glycerol. Oleic acid, pure or mixed with bees wax, has a plasticizing effect in the films, increasing their elasticity, flexibility and stretchability. The films with a 1:0.3:0.5 protein:glycerol:lipid ratio containing a 70:30 OA:BW ratio were the ones which showed the most adequate functional properties. (Young s Modulus: ± 9.36 MPa, Elongation at break: ± 2.05,). 27

18 Ozdemir and Floros (2008) investigated the effect of protein, sorbitol, bees wax and potassium sorbate concentrations in whey protein films. Protein, sorbitol and potassium sorbate were important factors influencing ultimate tensile strength, Young s modulus and elongation. Bees wax did not have an impact on ultimate tensile strength and Young s modulus, and it had little effect on elongation. Cao et al, (2007) found that in soy protein isolate gelatin composite edible film increasing gelatin ratio increased tensile strength (TS), elongation to break (EB), Young s modulus and swelling property of the SPI/gelatin composite films. Kristo, et al (2007) investigated mechanical properties of pullulan (P) and sodium caseinate (SC), as well as their blend and bilayer films plasticized with sorbitol (25 percent dry basis). Increasing the P/SC ratio decreased the Young s modulus (E), the tensile strength (rmax) and increased the percent elongation at break (percent EB), suggesting that P imparts flexibility and SC stiffness to the composite films. Sothornvit and Pitak (2007) investigated the effect of banana flour, glycerol (Gly) and pectin content on film oxygen permeability (OP) and mechanical properties of banana films. Increasing banana flour and pectin contents enhanced film strength; thus, it showed higher Young s modulus and tensile strength (TS) values but less percent elongation values. In contrast, increasing glycerol content reduced the film strength and improved film flexibility; therefore, it decreased EM and TS values but increased percent elongation values. Banana films showed good sealability, which can make these films suitable as sachets or pouches for dry foods, thus reducing the need for plastic materials. Srinivasa et al, (2007) prepared chitosan films by blending with polyols (glycerol, sorbitol and polyethylene glycol (PEG)) and fatty acids (stearic and palmitic acids). The tensile strength of the blended films decreased with the addition of polyols and fatty acids, whereas 28

19 the percent elongation was increased in polyol blend films, but fatty acid blend films showed no significant differences. Prodpran and Benjakul (2005) studied the effect of acid and alkaline solubilizing processes on the properties of the protein based film from threadfin bream surimi. Surimi films prepared from both processes had the similar light transmission, tensile strength (TS) and elongation at break (EAB). Increase in protein concentration resulted in an increase in TS, and EAB. Fakhouri, et al, (2004) developed and characterized composite biofilms using wheat gluten and cellulose acetate phthalate. They observed that an increase in gluten concentration in the composite films resulted in a decrease in tensile strength. There was no significant difference in elongation at break between the composite films. No difference in thickness was detected either. Turhan and Sahbaz (2004) investigated tensile strength (TS), percent elongation (E), in methylcellulose (MC) films plasticized by polyethylene glycol (PEG). TS determined to be between 17 and 44 N/mm 2 and percent E between 14 percent and 97 percent, depending on composition. Paramawati et al, (2003) prepared zein based edible films plasticized individually with 20 percent lauric acid; octanoic acid; triethylene glycol; polyethylene glycol, or lactic acid. They observed that all plasticizer indicated increased film flexibility and also affected tensile properties. Both octanoic acid and lactic acid increased all tensile parameters such as tensile strength (TS), puncture strength (PS) and elongation to break (ETB). Lauric acid exhibited improved TS and PS values. On the other hand triethylene glycol and polyethylene glycol did not affect the existing good performance of tensile properties of films, however, polyethylene glycol indicated excellent in improving film flexibility. 29

20 Rhim et al, (2002) determined the effect of sodium dodecyl sulfate (SDS) on selected physical properties of glycerin-plasticized soy protein isolate (SPI) films. Films were cast from heated (70 C for 20 min), alkaline (ph 10) aqueous solutions of SPI (5 g/100 ml water), glycerin (50 percent w/w of SPI), and SDS (0, 5, 10, 20, 30, or 40 percent w/w of SPI). SDS reduced film TS by as much as 43 percent for films with 40 percent SDS (6.2 vs MPa for control SPI films). In contrast, film E increased notably with addition of SDS even at 5 percent. Paramawati et al, (2001) observed the effects of the proportion of polyethylene glycol (PEG) and lauric acid (LA) used as composite plasticizer on mechanical properties of zein-based film. Flexibility of plasticized-zein films increased as the portion of PEG was increased, as shown by the trend of decreasing Young s modulus (EM) and increasing elongation to break (ETB). Tensile and puncture strength values were also affected by increase in the PEG portion, although they were not as consistent as EM and ETB values. Yang and Paulson (2000) incorporated bees wax or a 1:1 blend of stearic-palmitic acids (S-P) into gellan films through emulsifcation to form gellan/ lipid composite films. Addition of the lipids to gellan films lowered the mechanical properties and films with bees wax showed better mechanical properties overall than those with S-P acids. The tensile properties of gellan films containing 14.3percent bees wax were evaluated as a function of water activity (aw) of the film. Increasing the aw decreased the tensile strength (TS) and Young s modulus but tensile elongation was not affected. The extent of the decreases in TS for the composite film was less pronounced than that for a similar film without lipids, suggesting that lipids help to alleviate moisture sensitivity of gellan films. 30

21 Jangchud and Chinnan (1999) formed peanut protein films by using four types of plasticizer (glycerin, sorbitol, polyethylene glycol and propylene glycol)at three levels (0.67, 1.17, 1.67 g/g of protein content). Tensile strength decreased (from5.14 to 4.10 MPa), with an increase of glycerin from 1.17 to 1.67 g/g of protein and percent elongation increased (from 105 to 164 percent) when glycerin increased from 0.67 to 1.67 g/g of protein Banerjee and Chen (1995) compared the functional properties of whey protein concentrate films with those of the films derived from sodium caseinate, potassium caseinate, calcium caseinate, and whey protein isolate. The ultimate tensile strengths of simple whey protein concentrate films were similar to those of caseinate films. Whey protein concentrate films exhibited lower puncture strengths than did films from other milk proteins except simple film from sodium caseinate. Whey protein concentrate and isolate films had higher elongation values than did simple calcium caseinate films. Gennadios et al, (1993) evaluated the effect of ph of film forming solution of Soy protein isolate (SPI) and wheat gluten (WG) films. He found that SPI films prepared from ph 6 to 11 had significantly higher Tensile Strength(TS) and higher Elongation at break (E) than films from ph 1 to 3. WG films produced under alkaline conditions had significantly higher TS than films processed under acidic conditions. The research related to mechanical properties of edible film can be summarized as shown in Table

22 Sr No. Table 2.5 Review on Mechanical Properties of Edible Film Author Year Important finding 1 Fabra et al, 2008 Sodium caseinate films are affected by kind and ratio of plasticizer and lipids. 2 Ozdemir and Floros 2008 In whey protein film protein, sorbitol and potassium sorbate influence tensile strength, young s modulus and elongation. 3 Cao et al 2007 In soy protein isolate gelatin composite edible film increasing gelatin ratio increased tensile strength, elongation to break, Young s modulus and swelling property 4 Kristo, et al 2007 Increasing the Pullulan/Sodium Caseinate ratio decreases the Young s modulus, tensile strength) and increases the percent elongation at break. 5 Sothornvit and Pitak 6 Srinivasa et al 7 Prodpran and Benjakul 8 Fakhouri, et al 2007 Increasing banana flour and pectin contents enhances film strength while increasing glycerol content reduces film strength and improves film flexibility in banana flour based edible film The tensile strength of the blended chitosan films decreases with the addition of polyols and fatty acids, whereas the percent elongation increases in polyol blend films 2005 In case of protein based film from threadfin bream surimi increase in protein concentration resulted in an increase in TS, and EAB In wheat gluten and cellulose acetate phthalate composite film increase in gluten concentration results in decrease in tensile strength. 32

23 9 Turhan and Sahbaz 10 Paramawati et al 2004 Investigated tensile strength (TS), percent elongation (E), in methylcellulose (MC) films plasticized by polyethylene glycol (PEG) In zein based edible films all plasticizer increases film flexibility and also affected tensile properties. 11 Rhim et al 2002 In glycerin-plasticized soy protein isolate (SPI) films Sodium Dodecyl Sulphate (SDS) reduces film Tensile strength, while elongation at break increased notably with addition of SDS. 12 Paramawati et al, 13 Yang and Paulson 14 Jangchud and Chinnan 15 Banerjee and Chen 16 Gennadios et al 2001 Flexibility of plasticized-zein films increases as the amount of Polyethylene Glycol increases tensile and puncture strength values are also affected by increase in the PEG content, 2000 Addition of the lipids to gellan films lowers the mechanical properties and films with bees wax shows better overall mechanical properties than those with blend of stearic palmitic acids 1999 In peanut protein films tensile strength decreases with an increase of glycerin from 1.17 to 1.67 g/g of protein and percent elongation increases when glycerin increased from 0.67 to 1.67 g/g of protein 1995 Compared the functional properties of whey protein concentrate films with those of the films derived from sodium caseinate, potassium caseinate, calcium caseinate, and whey protein isolate SPI films prepared from ph 6 to 11 had significantly higher tensile strength and higher elongation at break than films from ph 1 to 3. 33

24 2.3 Preservation of Foods by Using Edible Coating /Film Edible films and coatings can be used to help in the preservation of fruit and vegetables because they provide a partial barrier to moisture, O2 and CO2, also improving mechanical handling properties, carrying additives, avoiding volatiles loss and even contributing to the production of aroma volatiles Edible surface coatings are applied to fruits to improve cosmetic features, such as sheen or perceived depth of colour, to reduce deterioration by suppressing water loss or to achieve modified atmosphere benefits. Application of edible coating for food preservation has been divided into following two subclasses Fruits and vegetables Other foods Fruits and Vegetables Fisk et al (2008) investigated calcium caseinate, chitosan, PrimaFresh 50-V, and SemperfreshTM edible coatings for their potential to enhance the quality and extend the storage life of hardy kiwifruit cv Ananasnaya.Coatings provided an attractive sheen to the fruit surface and did not impair ripening. The consumer test indicated that both coated and uncoated fruit were well liked. Geraldine et al, (2008) evaluated effects of agar-agar based (1 percent) coatings incorporated with 0.2 percent chitosan and 0.2 percent acetic acid on minimally processed garlic cloves. Moisture loss of coated garlic cloves was, on average, three times lower when compared to the control samples. There was a marked increase in color difference values for control cloves compared to the other treatments. Filamentous fungus and aerobic mesophilic were inhibited on garlic cloves coating incorporated with acetic acid + chitosan antimicrobial compounds. During 6 days-storage, at 25 0 C, the filamentous fungus and yeasts count was maintained between 10 2 and 10 3 CFU g -1 for the coated garlic cloves and around 10 6 CFU g -1 for the control. The coatings provided significant reduction in clove 34

25 respiration. Coated garlic cloves, had a respiration rate ( 30 mg CO2 h -1 kg -1 ) halved compared to the non-coated garlic cloves. Sothornvit and Rodsamran (2008) determined the effect of a mango edible film and storage conditions on fresh mango quality and shelf-life. A mango film provided a good oxygen barrier with sufficient mechanical properties to wrap whole and minimally processed mangoes. The film reduced weight loss and extended the ripening period of whole fresh mangoes. The shelf-life of unwrapped minimally processed mangoes kept in cellophane bags at room temperature (30 0 C) and cold storage (5 0 C) were 2 and 4 days, respectively. When the minimally processed mangoes were wrapped in a mango film and kept in cellophane bags, the shelf-life was extended to 5 and 6 days, when stored at 30 and 5 0 C, respectively. Tapia et al (2008) used alginate- (2% w/v) or gellan-based (0.5% w/v) coating formulations on fresh-cut papaya pieces. Formulations containing 2% (w/v) glycerol+1% ascorbic acid or 1% glycerol+1% ascorbic acid exhibited slightly improved water barrier properties for both types of coatings, as compared to the uncoated samples. The incorporation of 0.025% (w/w) sunflower oil into the alginate or the gellan-based formulations resulted in a 16% and 66% increase in the WVR of the coated samples, respectively. In general, coatings improved firmness of the fresh-cut product during the period studied. Furthermore, the addition of ascorbic acid as antioxidant in the coatings aided to preserve the natural ascorbic acid content of the freshcut papaya, helping to maintain its nutritional quality throughout storage. The gas barrier properties of the formulated coatings were not modified to allow substantial changes on respiratory rate and ethylene production of the coated papayas. Albanese et al (2007) observed the effect of trehalose as an edible coating on minimally processed Annurca apple slices during cold storage. During storage at 6 0 C the following parameters were monitored: weight loss, colour and whitening index (WI)), firmness, 35

26 malic and ascorbic acids, polyphenol content, microstructure by scanning electron microscopy (SEM) and microbial count. The results showed that such a coating reduced the browning phenomena; in fact the WI and hue values were significantly lower in coated samples than untreated ones. Moreover, decreases in weight loss and in the reduction of organic acids were observed in coated samples. Chien et al (2007) observed the effect of treatment of sliced mango with aqueous solutions of 0%, 0.5%, 1% or 2% chitosan and then stored at 6 0 C. Changes in the sensory qualities of taste, color and water loss, were evaluated. A chitosan coating retarded water loss and the drop in sensory quality, increasing the soluble solid content, titratable acidity and ascorbic acid content. It also inhibited the growth of microorganisms. Chlebowska-Smigiel et al, (2007) studied the influence of the pullulan and pullulan--protein edible coatings on the reduction of the apples mass loss during the storage. Pullulan edible coating significantly limited apples mass losses. Apples covered with coatings showed lower mass losses than the ones uncovered. The smallest mass losses were observed in apples covered with the coatings where the pullulan to protein ratios were: 6:4 and 5:5. It was observed that by adding protein to pullulan the coating stuck better to apples surface. During the storage process the protein-containing layer was less susceptible to crumbling and to peeling off. Olivas et al, (2007) investigated effectiveness of edible coatings made from alginate to preserve the quality of minimally processed Gala apples. Apple wedges were immersed in a calcium chloride solution and subsequently coated with one of three different coating formulations: alginate, alginate-acetylated monoglyceride-linoleic acid, and alginate-butter-linoleic acid. Overall, it was found that alginate coatings prolonged the shelf-life of cut apples without causing anaerobic respiration. All coatings used minimized the weight loss during storage, and apples with coatings containing acetylated 36

27 monoglyceride in particular remained the closest to original weight. Firmness of coated apples remained practically constant regardless of the type of coating, while control apples had a large decrease in firmness during storage. Browning of apple slices was retarded in all coated apples. A higher production of hexanol and trans-2-hexenal was observed in coated apples containing butter and acetylated monoglyceride. Durango et al (2006) developed an edible antimicrobial coating based on a starch chitosan matrix to evaluate its effect on minimally processed carrot by means of microbiological analyses. Coatings based on 4% yam starch (w/w) + 2% glycerol (w/w) and coatings based on 4% yam starch (w/w) + 2% glycerol (w/w) + chitosan in 0.5% and 1.5% concentrations were prepared. Samples of minimally processed carrot slices were immersed into these coatings. During storage, all the samples had counting <100 CFU/g for Staphylococcus aureus and <3 MPN/g for Escherichia coli. Starch + 0.5% chitosan coating controlled the growth of mesophilic aerobes, yeasts and molds and psychrotrophs during the first five days of storage, ultimately presenting reductions of only 0.64, 0.11 and 0.16 log cycles, respectively, compared to the control. Starch + 1.5% chitosan coated samples showed reductions in mesophilic aerobes, mold and yeast and psychrotrophic counting of 1.34, 2.50 and 1.30 log cycles, respectively, compared to the control. The presence of 1.5% chitosan in the coatings inhibited the growth of total coliforms and lactic acid bacteria throughout the storage period. Hernandez-Munoz et al, (2006) evaluated the effectivenss of 1 and 1.5 percent chitosan (CS) or chitosan combined with calcium gluconate to extend the shelf life of Strawberries. No sign of fungal decay was observed during the storage period for fruit coated with 1.5 percent CS (with or without the addition of CaGlu) or 1 percent CS percent CaGlu. By contrast, 12.5 percent of the strawberries coated with 1 percent CS lacking calcium salt were infected after five 37

28 days of storage. The chitosan coating reduced respiration activity, thus delaying ripening and the progress of fruit decay due to senescence. Strawberries coated with 1.5 percent chitosan exhibited less weight loss and reduced darkening than did those treated with 1 percent chitosan, independently of the presence or absence of CaGlu. However, addition of calcium to the 1 percent chitosan solution increased the firmness of the fruit. Martınez-Romero et al (2006) used a novel edible coating based on Aloe vera gel, as postharvest treatment to maintain sweet cherry quality and safety. During cold storage, uncoated fruit showed increases in respiration rate, rapid weight loss and colour changes, accelerated softening and ripening, stem browning and increased microbial populations, these processes being more intense during the shelf life periods. On the contrary, sweet cherry treated with A. vera gel significantly delayed the above parameters related to postharvest quality losses, and storability could be extended. The sensory analyses revealed beneficial effects in terms of delaying stem browning and dehydration, maintenance of fruit visual aspect without any detrimental effect on taste, aroma or flavours. Matuska et al (2006) found that coating of whole strawberries with selected edible (polysaccharide) films before osmotic processing favor water removal and prevent solute uptake. Among tested materials and coating procedures, double coating with a 0.5% sodium alginate (SA) solution gave the best results in terms of a high water loss (WL) to solid gain (SG) ratio (WL/SG). Single or double SA coating inhibited leakage losses upon freeze/thawing of osmotically treated strawberries. Vargas et al, (2006) used edible coatings based on high molecular weight chitosan combined with oleic acid to preserve quality of cold-stored strawberries. Coatings had no significant effects on acidity, ph and soluble solids contents of strawberries throughout storage. In contrast, coatings slowed down changes in the mechanical 38

29 properties and slightly modified respiration rates of samples. Addition of oleic acid not only enhanced chitosan antimicrobial activity but also improved water vapour resistance of chitosan-coated samples. Sensory analysis showed that coating application led to a significant decrease in strawberry aroma and flavour, especially when the ratio oleic acid:chitosan was high in the film. Del-Valle et al (2005) investigated use of prickly pear cactus mucilage (Opuntia ficus indica) as an edible coating to extend the shelf-life of strawberries. Different methods for mucilage extraction were tested in order to obtain the best coating. Edible films were tested to determine their effects on colour, texture and sensory quality of the fruit. From the results, it was concluded that the use of mucilage coatings leads to increased strawberry shelf life. Maftoonazad and Ramaswamy (2005) evaluated the effect of a methyl cellulose-based coating on the respiration rate, color and texture of avocados stored at room temperature. Coated avocados demonstrated lower respiration rates, greener color and higher firmness as compared with the uncoated control during the entire storage. The appearance of brown spots and mesocarp discoloration normally associated with fruit ripening were delayed in the coated fruits. Perez-Gago et al (2005) prepared edible composite coatings from whey protein isolate (WPI), whey protein concentrate (WPC) or hydroxypropyl methylcellulose (HPMC) as the hydrophilic phase, and bees wax (BW) or carnauba wax (CarW) as the lipid phase and coated on apple pieces. Results show that apple pieces coated with whey protein-based coatings had higher L, and lower b, a and Browning Index values than HPMC-based coated and uncoated apple pieces, which indicate that whey proteins exert an antibrowning effect. Coatings containing BW were more effective in decreasing enzymatic browning than coatings containing CarW. 39