Effects of partial hydrolysis and plasticizer content on the properties of film from cuttlefish (Sepia pharaonis) skin gelatin

Properties of film from cuttlefish (Sepia pharaonis) ventral skin gelatin with different degree of hydrolysis (DH: 0.40, 0.80 and 1.20%) added with glycerol as plasticizer at various levels (10, 15 and 20%, based on protein) were investigated. Films prepared from gelatin with all DH had the lower tensile strength (TS) and elongation at break (EAB) but higher water vapor permeability (WVP), compared with the control film (without hydrolysis) (p < 0.05). At the same glycerol content, both TS and EAB decreased, while WVP increased (p < 0.05) with increasing %DH. At the same DH, TS generally decreased as glycerol content increased (p < 0.05), however glycerol content had no effect on EAB when gelatins with 0.80 and 1.20% DH were used (p > 0.05). DH and glycerol content had no marked impact on color and the difference in color (ΔE^∗) of resulting films. Electrophoretic study revealed that degradation of gelatin and their corresponding films was more pronounced with increased %DH, resulting in the lower mechanical properties of films. Based on FTIR spectra, with the increasing %DH as well as glycerol content, higher amplitudes for amide-A and amide-B peaks were observed, compared with film from gelatin without hydrolysis (control film) due to the increased –NH₂ group caused by hydrolysis and the lower interaction of –NH₂ group in the presence of higher glycerol. Thermo-gravimetric analysis indicated that film prepared from gelatin with 1.20% DH exhibited the higher heat susceptibility and weight loss in the temperature range of 50–600 °C, compared with control film. Thus, both chain length of gelatin and glycerol content directly affected the properties of cuttlefish skin gelatin films.     

Mechanical and Barrier Properties of Lactic Acid and Rennet Precipitated Casein-Based Edible Films

Tensile strength (TS), percent elongation (%E), oxygen permeability (OP), and water vapor permeability (WVP) of lactic acid and rennet precipitated casein-based edible films were studied to determine the effect of protein to plasticizer ratio (0.6:1, 1:1, 1.4:1) and plasticizer type (sorbitol, glycerol) on these properties. TS increased (p<0.05) with increase in protein to plasticizer ratio. Sorbitol plasticized films were stronger (p<0.05) than glycerol plasticized films. However, films plasticized with glycerol were more extensible (p<0.05). Film %E decreased with increase in protein/plasticizer ratio for lactic acid casein films, whereas it increased for rennet casein films. Films plasticized with sorbitol were more effective (p<0.05) moisture and oxygen barriers than glycerol plasticized films. Overall, lactic acid casein films plasticized with sorbitol had the most effective mechanical and barrier properties.     

Starch-gelatin edible films: Water vapor permeability and mechanical properties as affected by plasticizers

Physical and mechanical properties of edible films based on blends of sago starch and fish gelatin plasticized with glycerol or sorbitol (25%, w/w) were investigated. Film forming solutions of different ratios of sago starch to fish gelatin (1:0, 2:1, 3:1, 4:1, and 5:1) were used and cast at room temperature. Amylose content of sago starch was between 32 and 34% and the protein content of the fish gelatin was found to be 81.3%. The findings of this study showed that the addition of fish gelatin in starch solutions has a significant effect (p < 0.05), resulting in films with lower tensile strength (TS) and higher water vapor permeability (WVP). On the other hand, increasing protein content (from 10.9% to 21.6%) in film samples plasticized with sorbitol showed significantly lower (p < 0.05) TS but no trend was observed in % elongation-at-break (EAB) and no differences in WVP. However, TS decreased with higher protein content in the samples when either plasticizers were used in general, but no significance differences was observed among the samples (p < 0.05) with glycerol with exception to film with high protein content (21.6%) only and no trend was observed in % EAB among samples as well. Significant difference (p < 0.05) was observed in TS and viscosity between different formulations with sorbitol. The morphology study of the sago starch/fish gelatin films showed smoother surfaces with decreasing protein in the samples with either plasticizer. DSC scans showed that plasticizers and protein content incorporated with sago starch films reduced the glass transition temperature (T_g) and melting temperature (T_m) and the melting enthalpy (ΔH_m). In this study, observation of a single T_g is an indication of the compatibility of the sago starch and fish gelatin polymers to form films at the concentration levels used.     

Mechanical Properties, Water Vapor Permeabilities and Solubilities of Highly Carboxymethylated Starch-Based Edible Films

ABSTRACT: Tensile strength (TS), elongation (E), water vapor permeabilities (WVP) and solubilities were determined for highly carboxymethylated starch (HCMS)-based edible films plasticized with sorbitol (S), xylitol (X), mannitol (M) and glycerol (G). TS and E of HCMS-based film increased as the concentration of plasticizer S, M or × increased. TS of the HCMS-based film containing combined plasticizers were higher than those of films containing single plasticizer. The WVP of HCMS-based films seemed to decreased as the concentration of M, X or G plasticizer increased. Increasing plasticizer concentrations in HCMS-based film resulted in decreasing solubility of the films.     

Alginate-calcium films: Water vapor permeability and mechanical properties as affected by plasticizer and relative humidity

Alginate films containing dissimilar amounts of guluronate (G) and mannuronate (M): M/G∼0.45 and M/G∼1.5, soaked in a calcium chloride solution up to 20 min were evaluated for water vapor permeability (WVP). M/G∼0.45 films proved to be better moisture barriers at all calcium immersion times compared to M/G∼1.5. WVP of M/G∼0.45 and M/G∼1.5 films decreased as time of immersion in calcium increased; after 3 min, a decrease in WVP was observed. M/G∼0.45 films soaked for 1 min in calcium were further analyzed to determine the effect of plasticizer and relative humidity (RH) on their mechanical properties and WVP, using fructose, glycerol, sorbitol, and polyethylene glycol (PEG-8000). Films without plasticizer showed a lower capacity to adsorb water compared to those with plasticizer. As RH increased, tensile strength (TS) decreased and elongation (E) increased for all films. This effect was more pronounced on films containing plasticizer, which had lower TS at all RHs. Plasticizer did not increase E at 58% RH. At 78% and 98% RH, glycerol, sorbitol and fructose showed a significant increase in E compared to PEG-8000 and no-plasticizer. PEG-8000 provided lower TS and E, while glycerol showed the highest among all plasticizers. There was no difference on WVP between no-plasticizer and glycerol. Fructose and sorbitol showed the lowest WVP while PEG-8000 showed the highest.     

Effects of plasticizers on the properties of edible films from skin gelatin of bigeye snapper and brownstripe red snapper

The effects of type and concentration of plasticizers on the mechanical properties (tensile strength, TS and elongation at break, EAB), water vapor permeability, light transmission, transparency and color of fish skin gelatin edible films from bigeye snapper (Priacanthus marcracanthus) and brownstripe red snapper (Lutjanus vitta) were investigated. At the same plasticizer concentration, fish skin gelatin films from both species plasticized with glycerol (Gly) showed the greatest EAB (P<0.05), whereas ethylene glycol (EG) plasticized films showed the highest TS (P<0.05). Films prepared from brownstripe red snapper skin gelatin exhibited slightly greater TS than those of bigeye snapper skin gelatin (P<0.05) when Gly and sorbitol (Sor) were used. EG, polyethylene glycol 200 (PEG 200) and polyethylene glycol 400 (PEG 400) affected the mechanical properties of both films differently. Films generally became more transparent and EAB, water vapor permeability (WVP), as well as light transmission of films increased, but TS and yellowness decreased with increasing plasticizer concentrations.     

Preparation and properties of dialdehyde carboxymethyl cellulose crosslinked gelatin edible films

Glycerol-plasticized gelatin edible films with a new kind of dialdehyde polysaccharide, dialdehyde carboxymethyl cellulose (DCMC) as crosslinking agent are successful prepared using casting techniques. The mechanical properties, thermal stability, light barrier properties, swelling behavior as well as water vapor permeability (WVP) of the gelatin-DCMC films are investigated. The results indicate that the addition of DCMC causes tensile strength (TS) and thermal stability to increase and elongation at break (EB) to decrease, suggesting the occurrence of crosslinking between gelatin and DCMC. The light barrier measurements present high values of transparency at 280 nm and low values of transparency at 600 nm of the gelatin-DCMC films, indicating that gelatin-DCMC films are very transparent (lower in transparency value) while they have excellent barrier properties against UV light. Moreover, the values of transparency at 280 nm increase with the increased DCMC and glycerol content, suggesting the potential preventive effect of gelatin-DCMC films on the retardation of product oxidation induced by UV light. Furthermore, the addition of DCMC can greatly decrease the water vapor permeability (WVP) and equilibrium swelling ratio (ESR) down to values about 1.5 × 10⁻¹⁰ g m/m² s Pa and 150%, revealing the potential of DCMC in reducing the water sensitivity of gelatin-based films. In common for hygroscopic plasticizer in edible films, the addition of glycerol gives increase of EB and WVP and decrease of thermal stabilities and ESR of the gelatin-DCMC films.     

Effects of plasticizers, pH and heating of film-forming solution on the properties of pea protein isolate films

Effects of glycerol (3-7% w/w) and sorbitol (4-8% w/w) concentration, pH (7.0, 9.0, 11.0) and heating (90 °C, 20 min) of film-forming solution (FFS) on the water vapor permeability (WVP), moisture content (MC), solubility, light transmission and transparency of pea protein isolate (PPI) films were investigated. Films plasticized with sorbitol exhibited significantly lower WVP, lower MC and higher solubility, in comparison with glycerol-plasticized films. Increasing glycerol content of the films led to increases in WVP and MC but did not affect film solubility. In contrast, increase in sorbitol content had no effect on permeability and MC but resulted in increased film solubility. Moisture sorption isotherms of PPI films suggested that the difference in WVP observed among films plasticized with glycerol and sorbitol might be due to the different hygroscopicity of these plasticizers. The pH of FFS did not have a significant effect on WVP and MC. Solubility of PPI films formed from non-heated FFS was not affected by pH, whereas solubility of films formed from heat-treated FFS generally increased when pH was increased from 7.0 to 11.0. Heating of FFS resulted in improved film transparency. All tested films were characterized by excellent ability to absorb UV radiation. Microstructural observation by scanning electron microscopy did not show differences between sorbitol- and glycerol-plasticized films.     

Development and characterization of a novel biodegradable edible film obtained from psyllium seed (Plantago ovata Forsk)

In this study, the physical, thermal and mechanical properties of a novel edible film based on psyllium hydrocolloid (PH) were investigated. PH films were prepared by incorporation of three levels of glycerol (15%, 25%, and 35% w/w). As glycerol concentration increased, water vapor permeability (WVP), percent of elongation (E%) and water solubility of PH films increased whilst, tensile strength (TS), surface hydrophobicity and glass transition point (T_g) decreased significantly. At the level of 15% (W/W) of glycerol, PH films showed the lowest WVP values (1.16 × 10⁻¹⁰ g H₂O m⁻² s⁻¹ MPa⁻¹), E% (24.57%) and water solubility (47.69%) and the highest values for TS (14.31 MPa), water contact angle (84.47°) and T_g (175.2 °C). By increasing glycerol concentration, PH films became slightly greenish and yellowish in color but still transparent in appearance. This study revealed that the psyllium hydrocolloid had a good potential to be used in producing edible films with interesting specifications.     

Mechanical and Thermal Characteristics of Pea Starch Films Plasticized with Monosaccharides and Polyols

Edible starch films were produced from pea starch and various plasticizers (mannose, glucose, fructose, and glycerol and sorbitol) at the ratio of 4.34, 6.50, 8.69, and 10.87 mmol plasticizer per gram of starch. After film specimens were conditioned at 50% relative humidity, mechanical properties (tensile strength, elongation, and modulus of elasticity), water vapor permeability (WVP), moisture content, and thermomechanical properties (G’ and tan8) were determined as a function of plasticizer concentration. At all concentration levels, monosaccharides (mannose, glucose, and fructose) made the starch films stronger (higher tensile strength) and more stretchable than polyols (glycerol and sorbitol), while WVP of monosaccharide‐plasticized starch films were lower than those of polyol‐plasticized starch films, especially at higher plasticizer concentration levels. Except for 4.34 mmol/g of mannose‐plasticized film, all the other films showed similar modulus of elasticity at the same plasticizer concentration. Polyol‐plasticized films had lower T than the monosaccharide‐plasticized films. Glucose‐ and sorbitol‐plasticized films needed more activation energy to go through glass transition than others. After all, research results showed that not only the polyols but also the monosaccharides were effective in plasticizing starch films. It is concluded that molecular size, configuration, total number of functional hydroxyl group of the plasticizer as well as its compatibility of the plasticizers with the polymer could affect the interactions between the plasticizers and starch molecules, and consequently the effectiveness of plasticization.     

Water Vapor Permeability and Mechanical Properties of Soy Protein Isolate Edible Films Composed of Different Plasticizer Combinations

Water barrier and mechanical properties were measured for soy protein isolate (SPI) films plasticized with glycerol (GLY) and 1 of the plasticizers (propylene glycol [PG], polyethylene glycol [PEG], sorbitol [SOR], or sucrose [SUC]) at a ratio of 25:75, 50:50, 75:25, and 0:100. Plasticizer type as well as the plasticizer ratio in the GLY: plasticizer mixtures affected the film water barrier and mechanical properties. An addition of as little as 25% of a less hygroscopic plasticizer in the mixture induced significant reduction in water vapor permeability (WVP) of SPI films. However, at least 50% of the mixture needs to be GLY to show significant improvement in tensile strength (TS). From our experimental design, 50:50 GLY:SOR was the recommended combination because of its comparatively low WVP value and relatively high flexibility and strength. Incompatibility of GLY:PEG plasticizer mixture in SPI film was observed by surface migration of PEG from the film matrix.     

Properties and antioxidant activity of fish skin gelatin film incorporated with citrus essential oils

Properties of protein-based film from fish skin gelatin incorporated with different citrus essential oils, including bergamot, kaffir lime, lemon and lime (50% based on protein) in the presence of 20% and 30% glycerol were investigated. Films containing 20% glycerol had higher tensile strength (TS) but lower elongation at break (EAB), compared with those prepared with 30% glycerol, regardless of essential oils incorporated (p < 0.05). Films incorporated with essential oils, especially from lime, at both glycerol levels showed the lower TS but higher EAB than the control films (without incorporated essential oil) (p < 0.05). Water vapour permeability (WVP) of films containing essential oils was lower than that of control films for both glycerol levels (p < 0.05). Films with essential oils had varying ΔE^* (total colour difference), where the highest value was observed in that added with bergamot essential oil (p < 0.05). Higher glycerol content increased EAB and WVP but decreased TS of films. Fourier transforms infrared (FTIR) spectra indicated that films added with essential oils exhibited higher hydrophobicity with higher amplitude at wavenumber of 2874–2926 cm⁻¹ and 1731–1742 cm⁻¹ than control film. Film incorporated with essential oils exhibited slightly lower thermal degradation resistance, compared to the control film. Varying effect of essential oil on thermal degradation temperature and weight loss was noticeable, but all films prepared using 20% glycerol had higher thermal degradation temperature with lower weight loss, compared with those containing 30% glycerol. Films added with all types of essential oils had rough cross-section, compared with control films, irrespective of glycerol levels. However, smooth surface was observed in all film samples. Film incorporated with lemon essential oil showed the highest ABTS radical scavenging activity and ferric reducing antioxidant power (FRAP) (p < 0.05), while the other films had lower activity. Thus, the incorporation of different essential oils and glycerol levels directly affected the properties of gelatin-based film from fish skin.     

Development of fish gelatin edible films using extrusion and compression molding

Fish gelatin was plasticized with 20% and 25% glycerol (w/w of gelatin) and used to develop edible films by twin-screw extrusion at 110 and 120 °C followed by compression molding at 80 °C. Tensile and moisture barrier properties and glass transition temperature were then measured and compared with solution-cast films. The films extruded at 110 °C and with 25% glycerol had the highest percent elongation at break of 293 ± 27%. The water vapor permeability values of extruded films (the highest value being 2.9 ± 0.2 g mm h⁻¹ cm⁻² Pa⁻¹) were higher than those of solution-cast films while the glass transition temperatures (T_g) of the extruded films were generally lower than those of solution-cast films. Films with 25% glycerol that were extruded at 110 °C had the lowest T_g (2.10 ± 0.31 °C). This investigation showed that extrusion processing followed by compression molding is a feasible method to produce fish gelatin films for commercial applications in a wide range of food products.     

Properties of film from cuttlefish (Sepia pharaonis) skin gelatin incorporated with cinnamon,clove and star anise extracts

Properties of film from cuttlefish (Sepia pharaonis) ventral skin gelatin without and with partial hydrolysis (1.2% degree of hydrolysis) incorporated with 1% ethanolic extract of cinnamon (CME), clove (CLE) and star anise (SAE) were determined. Films with different herb extracts (without and with oxidation) had higher tensile strength (TS) but lower elongation at break (EAB), compared with the control film (without addition of herb extracts) (p < 0.05). Lower water vapor permeability (WVP) and L^∗-value but higher b^∗- and ΔE^∗-values were observed when the extracts were incorporated (p < 0.05). Electrophoretic study revealed that cross-linking was pronounced in films containing different herb extracts. Oxidized extracts yielded films with higher TS and WVP than those without oxidized herb extracts (p < 0.05). Generally, similar properties were noticeable for films from gelatin with and without partial hydrolysis. Nevertheless, higher mechanical properties were obtained for the latter. FTIR spectra indicated that protein–polyphenol interactions were involved in the film. Thermo-gravimetric analysis revealed that films incorporated with SAE or SAE with oxidation (OSAE) exhibited lower heat susceptibility and weight loss in the temperature range of 50–600 °C, compared with control film. Films with SAE and OSAE had smoother surface for gelatin without hydrolysis; however, coarser surface was observed in film from gelatin with partial hydrolysis. Thus, the incorporation of different herb extracts directly affected the properties of film from cuttlefish skin gelatin with and without hydrolysis.     

Effects of various plasticizers on mechanical and water vapor barrier properties of gelatin films

Different kinds of plasticizers were chosen to study the effects of plasticizer composition, size and shape on the mechanical properties and water vapor permeability (WVP) of gelatin films in this paper. Firstly, oligosaccharides – sucrose, and some organic acids such as oleic acid, citric acid, tartaric acid, malic acid (MA) were added to gelatin. It was found that only MA could improve the ductility of gelatin film, and the visual appearance of MA modified gelatin film was better. Secondly, polyethylene glycols (PEG) with different molecular weights (300, 400, 600, 800, 1500, 4000, 10?000, 20?000) were used to plasticize gelatin films. This showed that PEG of lower molecular weights exhibited better plasticizing effect for gelatin films, and such films had better visual properties. This shows that mannitol (Man) and sorbitol (Sor) could make gelatin films flexible, whereas Man could crystallize from gelatin film. Following this, the plasticization of ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG) series and ethanolamine (EA), diethanolamine (DEA), triethanolamine (TEA) series was studied. At last, suitable plasticizers (MA, PEG300, sorbitol, EG, DEG, TEG, EA, DEA, TEA) for gelatin were selected to investigate the WVP and water content of these plasticized gelatin films. The mechanical properties of these films were also compared.     

Effect of plasticizer content on the functional properties of extruded gelatin-based composite films

Beef gelatin, in combination with varying levels of glycerol, was used to manufacture films by extrusion. A twin-screw co-rotating extruder was employed to produce the films and the mechanical and barrier properties of the films were investigated. Increasing the plasticizer content increased (P < 0.05) elongation at break (EAB) values but decreased (P < 0.05) tensile strength (TS) values. Oxygen permeability (OP) values for gelatin-based composite films increased (P < 0.05) as the concentration of glycerol increased. Additionally, the solubility of films in water and seal strength increased as glycerol content increased. FTIR results indicated that increasing glycerol concentration increased and displaced the peak situated around 1032 cm⁻¹, which corresponded to glycerol. Gelatin-based composite films with a concentration of 0.2% glycerol possessed the lowest water vapor permeability (WVP) and OP values. From the data generated in this study, it is clear that the use of a plasticizing agent in film formulations should be carefully considered because of the negative effects that the plasticizing agent could have on extruded film barrier properties.     

Tensile, water vapor barrier and antimicrobial properties of PLA/nanoclay composite films

PLA-based composite films with different types of nanoclays, such as Cloisite Na⁺, Cloisite 30B and Cloisite 20A, were prepared using a solvent casting method and their tensile, water vapor barrier and antimicrobial properties were tested. Tensile strength (TS), elongation at break (E), and water vapor permeability (WVP) of control PLA film were 50.45 ± 0.75 MPa, 3.0 ± 0.1%, and 1.8 × 10⁻¹¹ g m/m² s Pa, respectively. TS and E of nanocomposite films prepared with 5 g of clay/100 g of PLA decreased 10-20% and 11-17%, respectively, depending on the clays used. On the contrary, WVP of the nanocomposite films decreased 6-33% through nanoclay compounding. Among the clay types used, Cloisite 20A was the most effective in improving the water vapor barrier property while sacrificing tensile properties the least. The effect of clay concentration tested using Cloisite 20A showed a significant decrease in TS and WVP, with increases in clay content. Among the PLA/clay composite films tested, only PLA/Cloisite 30B composite film showed a bacteriostatic function against Listeria monocytogenes.     

Edible films made from blends of manioc starch and gelatin – Influence of different types of plasticizer and different levels of macromolecules on their properties

The interest in the development of edible and biodegradable films has increased because it is every day more evident that non-degradable materials are doing much damage to the environment. In this research, bioplastics were based on blends of manioc starch (native and modified) and gelatin in different proportions, added of glycerol or sorbitol, which were used as plasticizers. The objective was to study the effect of two different plasticizers, glycerol and sorbitol, and different concentrations of starch and gelatin on the barrier (water vapor permeability – WVP), mechanical (tensile strength and elongation at break), physicochemical (solubility in water and in acid) and physical properties (opacity and thickness) of the obtained bioplastics samples. As a result, all of them showed transparency and resistance to tensile strength, as well as increasing in thickness values and in the WVP, as the gelatin content increased in the formulations. Finally, all results for tensile strength and elongation at break obtained for those samples plasticized with sorbitol were better than those plasticized with glycerol.     

Preparation of a barley bran protein–gelatin composite film containing grapefruit seed extract and its application in salmon packaging

The physical properties of a composite film prepared from barley bran protein and gelatin (BBG) were investigated. Tensile strength (TS) and elongation at break (E) values of the BBG film decreased as barley bran protein content increased. TS increased with increasing gelatin content, but E values decreased. The optimal conditions for the preparation of the BBG film were 3 g barley bran protein, 3 g gelatin, and 1 g sorbitol in 100 mL film-forming solution. In order to inhibit the growth of pathogenic bacteria, a BBG film containing grapefruit seed extract (GSE) was prepared. After 15 days of storage, populations of Escherichia coli O157:H7 and Listeria monocytogenes inoculated on salmon packaged with the BBG film containing GSE decreased by 0.53 and 0.50 log CFU/g, respectively, compared to the control. Also, packing salmon with the BBG film containing GSE decreased the peroxide value and thiobarbituric acid value by 23.0% and 23.4%, respectively.     

Thermal,mechanical and water adsorption properties of corn starch–carboxymethylcellulose/methylcellulose biodegradable films

The objective of this study was to investigate the effect of the addition of methylcellulose and carboxymethylcellulose on the thermal, mechanical and water adsorption properties of starch-based films plasticized with glycerol or polyethylene glycol (PEG). Mechanical tests showed that as the methylcellulose and carboxymethylcellulose proportion increased, starch films became more resistant to break, resulting in higher TS values. Besides there has been a positive effect on the elasticity of starch films realized by a considerable increase in E% values. Depending on the plasticizer type, either single or dual glass transitions were seen in DSC thermograms. One glass transition temperature was observed for films plasticized with glycerol, on the contrary, dual glass transitions were detected for PEG plasticized films. This behavior was attributed to the phase separation of the PEG. In addition, the presence of an endothermic peak in the thermograms of PEG plasticized films was taken as another indicator of the phase separation. As a result, it was suggested that PEG was not as compatible as glycerol with the composite polysaccharide matrix and plasticizer type was the main factor that shaped the thermal profiles of the film samples. Water adsorption isotherm data showed that samples displayed nonlinear sorption profile which is typical for hydrophilic films. In all films tested, equilibrium moisture contents, increased almost linearly up to a a_w of 0.65–0.85, beyond where a sharp increase was noted. Adsorption data was adequately fitted by BET and GAB models. Eventually, it can be concluded that film forming properties of starch can be improved by incorporation of methylcellulose and carboxymethylcellulose to the polymer matrix.