Mechanical and barrier properties of biodegradable soy protein isolate-based films coated with polylactic acid

Polylactic acid (PLA)-coated soy protein isolate (SPI) films were prepared by dipping SPI film into PLA solution. The effects of coating on improvements in mechanical and water barrier properties of the film were tested by measuring selected film properties such as tensile strength (TS), elongation at break (E), water vapor permeability (WVP), and water solubility (WS). TS of SPI films increased from 2.8±0.3 up to 17.4±2.1 MPa, depending on the PLA concentration of the coating solution, without sacrificing the film's extensibility. In contrast, the extensibility of SPI film coated with solution containing more than 2 g PLA/100 ml solvent, increased. WVP of PLA-coated SPI films decreased from 20 to 60 fold, depending on the concentration of PLA coating solution. Water resistance of SPI films was greatly improved as demonstrated by the dramatic decrease in WS for PLA-coated films. The improvement in water barrier properties was mainly attributed to the hydrophobicity of PLA.     

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.     

The water vapour permeability,mechanical properties and solubility of fish gelatin–chitosan films modified with transglutaminase or 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and plasticized with glycerol

The effect of glycerol on the mechanical and water barrier properties, as well as on the water solubility, of fish gelatin–chitosan films (4:1, w/w) cross-linked with TGase or EDC was determined. The addition of glycerol in concentrations up to 30% (of the substrate mass) to the fish gelatin–chitosan films modified with TGase or EDC did not change their solubility in buffers of pH 3 and 6 at 25 °C or during heating at 100 °C for 60 min. The chemical and enzymatic cross-linking of the components did not increase the water barrier properties of the films. WVP of the films modified with EDC and TGase was not affected by glycerol at concentrations up to 25% of the substrate mass. Tensile strength of the films decreased after modification of the components with TGase or EDC, respectively, by about 25% and 40%. The elongations of the enzymatically modified films containing 20% of glycerol and of chemically modified films containing 15% of glycerol were, respectively, about 8 and 13 times higher than those of unplasticized films; however, the tensile strengths of plasticized films were, respectively, 2.5 and 5 times lower.     

Structure-modifying alkaline and acidic pH-shifting processes promote film formation of soy proteins

The effect of pH-shifting, a process that induces the molten globule state in proteins, on the film-forming potential of soy protein isolate (SPI) at different temperatures was investigated. Partial unfolding at pH 1.5 or 12, followed by refolding at pH 7.0, was performed to alter the protein structure. Glycerin-plasticised films were prepared from pH-treated SPI at ambient temperature (20 °C), or by heating at 50, 60, 70, or 80 °C (30 min). Tensile strength (TS), elongation at break (EAB), water vapour permeability (WVP), protein solubility (pH 3–7), and non-participating proteins of films were analysed, and the film microstructures were examined. The pH₁₂-treated SPI spontaneously formed a transparent, slightly yellowish film at 20 °C, which had the greatest EAB, while pH_1.5-treated and native SPIs required preheating at 50 and 70 °C, respectively, to form a film. Heating generally decreased solubility and WVP but increased TS. Films formed from both pH₁₂- and pH_1.5-treated SPIs were more elastic (up to 2-fold greater in EAB, P < 0.05) than the film formed from untreated SPI despite slightly reduced TS and WVP. Electrophoresis revealed disulphide bonds between A and B subunits of glycinin being a dominant force in pH₁₂- and pH_1.5-treated SPI films, while noncovalent forces were abundant in untreated SPI films. The pH₁₂-treated SPI film consisted of more interactive protein strands than other SPI films, which seemed to explain its superior elastic properties.     

Physical properties and sensory evaluation of WPI films of varying thickness

The effect of varying thickness on the water barrier properties, tensile properties and sensory characteristics of glycerol-plasticised whey protein isolate (WPI) films was investigated. Thickness was varied by preparing films with increasingly dilute film forming WPI solutions in the range 9.5-2.3 g protein/100 g. All films had a glycerol to protein ratio of 0.37 (Gly: Pro). Tensile strength (TS), elastic modulus (EM) and film permeance were unaffected by film thickness but maximum load (ML) and % elongation (E) decreased (P<0.05) with decreasing thickness. In a sensory test with crackers and melted cheese, panelists could readily detect the thickest films (79 μm) but not the thinnest films (23 μm) (P<0.05). The results indicate that reducing the thickness of glycerol plasticised WPI films makes them less perceptible in a food system while maintaining moisture barrier and certain tensile properties.     

Edible oxygen barrier bilayer film pouches from corn zein and soy protein isolate for olive oil packaging

An edible oxygen barrier film pouch was fabricated from a heat sealable corn zein (CZ) layer laminated on soy protein isolate (SPI) film and used to package olive oil condiments for use with instant noodles. The mechanical, barrier, and physical properties of the CZ/SPI bilayer films were then investigated and the oxidative stability of olive oil in the pouches was measured during storage under dry and intermediate relative humidity conditions. When compared to the SPI film, lamination with an additional layer of CZ film led to increased tensile strength and water barrier properties, while it had a lower elongation at break and decreased oxygen barrier properties. Nevertheless, the oxygen permeability of the CZ/SPI film (0.81 × 10⁻¹⁸ m³ m/m² s Pa) was lower than that of nylon-metalocene catalyzed linear low-density polyethylene (NY/mLLDPE) film (3.51 × 10⁻¹⁸ m³ m/m² s Pa) which is the material usually used for such condiments. The CZ/SPI bilayer films generated here were heat sealable at 120-130 °C and produced a seal strength greater than 300 N/m. The higher oxygen barrier property of the CZ/SPI bilayer films resulted in reduced oxidative rancidity of olive oil packaged in the CZ/SPI film when compared to olive oil packaged in NY/mLLDPE films.     

Effect of phenolic compounds on the properties of porcine plasma protein-based film

Properties of porcine plasma protein-based film incorporated with tannic acid, caffeic acid and ferulic acid at different concentrations (1–3% (w/w) of protein content) were studied. Film-forming solution (FFS) containing 3% protein (w/v) and 70% glycerol (w/w of protein content) was preheated at 70 °C for 30 min and adjusted pH to 10 followed by the addition of phenols and film casting. Tensile strength (TS) of resulting film increased by 123.3, 194.3 and 19.5% and elongation at break (EAB) increased by 71.1, 86.3 and 10.2%, respectively, compared with the control film, when tannic acid, caffeic acid and ferulic acid at a level of 3% was added. The use of all phenolic compounds slightly increased water vapor permeability (WVP) of resulting films (p < 0.05). The increases in a^∗- and b^∗-values of films were observed as the higher concentrations of tannic acid and caffeic acid were used. This was associated with the lowered transparency of resulting films. FFS containing 3% caffeic acid with prior oxygenation, especially with pH 10, yielded the film with increased TS but lowered EAB (p < 0.05). Oxygenation of FFS was associated with the lower L^∗-value and higher a^∗-value of resulting films. Therefore, phenolic compounds could be used as natural cross-linkers which affected the properties of porcine plasma protein-based film differently.     

Mechanical and water vapor barrier properties of extruded and heat-pressed gelatin films

Gelatin-based edible films were produced by extruding hot melt of gelatin-based resins through a die with slot orifice and followed by heat-pressed method. The resins were plasticized with glycerol, sorbitol and the mixture of glycerol and sorbitol (MGS). The effect of type of plasticizer on extruded and heat-pressed (EHP) film-forming capacity was studied, and the mechanical and water barrier properties of resulting EHP gelatin films were compared with those of gelatin films prepared by solution casting method. Stretchable films were formed when glycerol or MGS were used as plasticizer, whereas resins plasticized with sorbitol were extruded in non-stretchable sheets. Glycerol plasticized gelatin film showed the highest flexibility and transparency among the EHP films tested. Tensile strength (TS), elongation (E) and water vapor permeability (WVP) of glycerol plasticized EHP gelatin films were 17.3 MPa, 215.9% and 2.46 ng m/m² s Pa, respectively, and EHP gelatin films had higher E values, lower TS values and higher WVP values compared to the glycerol plasticized cast gelatin films.     

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 properties and water vapor permeability of edible films made from fractionated soy proteins with ultrafiltration

Soy protein isolates (SPI) were fractionated by ultrafiltration unit equipped with 100 and 300 kDa cutoff size membranes. Glycerol-plasticized fractionated soy protein films were developed by casting methods. Mechanical, moisture barrier and physical properties of films, as affected by molecular weight of soy protein fraction, were investigated. Tensile strength and percent elongation at break of films increased with molecular weight of soy proteins. However, molecular weight variation did not influence the water vapor barrier properties of films. Protein solubilities of fractionated films were in the range of 3.5-4.6 g/100 g of dry film, whereas 11.9 g of proteins were solubilized from 100 g of dry SPI film. Hunter b value of fractionated protein films decreased with molecular weight of soy protein.     

The physicochemical characteristics and hydrophobicity of high amylose starch–glycerol films in the presence of three natural waxes

The film forming behaviour and hydrophobicity of high amylose (HA) starch in the presence of three different natural waxes (beeswax, candelilla wax and carnauba wax) were studied in the presence and absence of Tween-80. The HA starch:glycerol (G) ratio was maintained at 80:20 (on dry solid basis) and the concentration of wax was varied from 5% and 10% (w/w). The melted wax samples were homogenized with HAG dispersion with or without Tween-80 and the films were prepared by solution casting. The hydrophobicity and water-barrier properties in these films were determined by using contact angle (CA), water vapour permeability (K_w) tests, and water sorption isotherm at 0.529 RH and 20 °C. The K_w values of the HAG films decreased significantly (p < 0.05) with the addition of 5% concentration of these waxes. Then the addition of Tween-80 to the HAG + wax films increased the K_w values significantly (p < 0.05). The presence of these waxes in the presence and absence of Tween-80 resulted into different sorption isotherms and the water adsorptivity and moisture diffusion coefficient values were also affected. The presence of Tween-80 increased the CA in HAG + carnauba wax films while the CA was found to decrease in the case of other two waxes. The highest hydrophobicity was observed in HAG + carnauba wax + Tween-80 films in which the CA was >80.0° both at 5% and 10% (w/w) wax concentration. These higher CA values in HAG + carnauba wax + Tween-80 films were found to be related to the higher surface roughness in these films.     

Influence of heating,protein and glycerol concentrations of film-forming solution on the film properties of Argentine anchovy (Engraulis anchoita) protein isolate

This study was conducted to evaluate the influence of thermal treatment (74, 82, and 90 °C), glycerol (30%, 35%, and 40%, w/w) and protein concentrations (3.0%, 3.5%, and 4.0% w/w) of film-forming solution on the properties of Argentine anchovy (Engraulis anchoita) protein isolate (API) films produced by casting. The API presented 88.8% of proteins, 5.5% moisture, 1.3% lipids, 1.0% ash and 53.3% of polar amino acids. The DSC of protein isolate was observed at maximum temperature of 62.2 °C and ΔH 6.4 J/g. The thickness, water vapor permeability, color difference and opacity of the films were not affected by the experimental variables studied (p > 0.05). The lowest solubility, elongation, and highest tensile strength of the films occurred at low temperature, low protein and glycerol concentrations (p < 0.05). Micrographs obtained by scanning electron microscopy of the films showed homogeneous surfaces at low temperature.     

Protein and glycerol contents affect physico-chemical properties of soy protein isolate-based edible films

This study was conducted to determine the effect of both soy protein and glycerol contents on physico-chemical properties of soy protein isolate-based edible (SPI) films. The aim of this study was to better understand the influence of SPI and GLY contents on the behavior of the physico-chemical properties of soy protein isolate-based films. Films were casted from heated (70 °C for 20 min) alkaline (pH 10) aqueous solutions of SPI at 6, 7, 8, and 9 (w/w %), glycerol (50%, w/w, of SPI) and SPI at 7 (w/w %), glycerol (40, 60, 70 %, w/w of SPI). Water vapor permeability (WVP), was measured at 25 °C and for four different relative humidities (30–100%, 30–84%, 30–75%, 30–53%). Surface properties and differential scanning calorimetry were also measured. Varying the proportion of SPI and GLY had an effect on water vapor permeability, wetting and thermal properties of SPI films. A synergistic effect of glycerol and protein was observed on the water vapor permeability. Glycerol and RH gradient strongly enhance the moisture absorption rates and permeability of SPI based films. SPI content weakly increases the WVP and does not modify the surface properties. The temperature of denaturation of soy protein decreases glycerol content except for the higher concentration whereas it increases with protein ratio.Industrial relevanceThis topic of research aims to control mass transfers within composite foods or betweenfoods and surrounding media (for instance the headspace in packagings). The targeted applications from this work deals with the food product coating or the coating of paper-based packaging for limiting both the loss of water and flavors by cheese based products. This will allow to maintain the weight of the cheese during “ripening” and commercialization, and also to prevent (off-) flavour dissemination from very odorant cheese as produced in France and Poland.     

Effect of some factors and pretreatment on the properties of porcine plasma protein-based films

The properties of porcine plasma protein-based films as influenced by some factors and pretreatment were studied. Both protein concentrations (20 and 30 g L⁻¹) and glycerol contents (50, 60 and 70 g/100 g protein) had the impact on film properties. Film prepared from film-forming solution (FFS) containing protein (30 g L⁻¹) and glycerol (60 g/100 g protein) possessed the highest tensile strength (TS) (2.48 MPa), while that containing protein (30 g L⁻¹) and glycerol (70 g/100 g protein) exhibited the greatest elongation at break (EAB) (18.33%). Protein and glycerol contents affected water vapor permeability (WVP) and transparency of the resulting films. No differences in protein solubility were found among all films (p > 0.05). Pretreatment of FFS by adjusting pH (2-11) and heating at different temperatures (40, 55 and 70 °C) on the properties of the resulting films was investigated. TS and EAB became higher but WVP decreased with decreasing or increasing pH value of FFS. Heat treatment of FFS with pH 3 and 10 had no impact on TS of the resulting film (p > 0.05). On the other hand, EAB and WVP increased with increasing temperature of FFS at both pHs (p < 0.05).     

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.     

Influences of degree of hydrolysis and molecular weight of poly(vinyl alcohol) (PVA) on properties of fish myofibrillar protein/PVA blend films

Biodegradable blend films based on fish myofibrillar protein (FMP) and poly(vinyl alcohol) (PVA) were prepared and characterized. PVA with different degrees of hydrolysis (DH) and molecular weights (MW) had the impact on properties of FMP/PVA (1:1, w/w) blend film. The blend films with higher MW of PVA were more tensile resistant, as indicated by the greater tensile strength (TS) and elongation at break (EAB), while the films with PVA of lower DH were more flexible. The blend film with PVA-BP26 (DH: 86–98% mol; MW: 124,000–130,000 g/mol) exhibited the greatest tensile performance and the lowest water vapor permeability (p < 0.05), compared with other films. SEM and FTIR results revealed that FMP and PVA were compatible and their intermolecular interaction was enhanced, providing the blend film with desirable properties. Therefore, incorporation of PVA with appropriated DH and MW could improve the properties of the FMP-based film.     

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.     

Physico-mechanical properties of chitosan films with carvacrol and grape seed extract

The physico-mechanical properties of 3 films composed by carvacrol, grape seed extract (GSE) and chitosan in different proportions were studied. The films, prepared by solvent casting technique with the following compositions of the casting solutions in carvacrol, GSE and chitosan: film-1: 9.6 ppm–684 ppm–1.25% w/v, film-2: 60 ppm–400 ppm–1.2% w/v and film-3: 90 ppm–160 ppm–1.24% w/v and were compared to a control (1.25% w/v chitosan) film. Mechanical, structural, barrier and colour properties of the films were evaluated. Film-3 presented the lowest water vapour and carbon dioxide permeabilities (WVP and CO₂P) and tensile strength (TS) values and the highest oxygen permeability (O₂P), whereas film-1 presented the highest water content and the lowest crystallinity, CO₂P, TS and luminosity. These results suggest that in the range studied, carvacrol and GSE affect the film structure and its mechanical properties due to hydrophilic (GSE) and hydrophobic (carvacrol) compounds. This work will help the development of edible films, based on physico-mechanical properties, contributing to food preservation and shelf-life extension.     

Effect of heat treatment of film-forming solution on the properties of film from cuttlefish (Sepia pharaonis) skin gelatin

Effects of heat treatment at different temperatures (40–90 °C) of film-forming solution (FFS) containing 3% gelatin from cuttlefish (Sepia pharaonis) ventral skin and 25% glycerol (based on protein) on properties and molecular characteristics of resulting films were investigated. The film prepared from FFS heated at 60 and 70 °C showed the highest tensile strength (TS) with the highest melting transition temperature (T_max) (p < 0.05). Nevertheless, film from FFS heated at 90 °C had the highest elongation at break (EAB) with the highest glass transition temperature (T_g) (p < 0.05). With increasing heating temperatures, water vapor permeability (WVP) of films decreased (p < 0.05), but no differences in L*-value and transparency value were observed (p > 0.05). Based on FTIR spectra, the lower formation of hydrogen bonding was found in film prepared from FFS with heat treatment. Electrophoretic study revealed that degradation of gelatin was more pronounced in FFS and resulting film when heat treatment was conducted at temperature above 70 °C. Thus, heat treatment of FFS directly affected the properties of resulting films.     

大豆蛋白基明胶复合膜性能稳定性分析

以大豆蛋白和明胶为主要原料,采用戊二醛溶液交联方式和戊二醛饱和蒸汽交联制备大豆蛋白基明胶复合膜,通过对两种交联方式制备的复合膜机械性能稳定性和降解性测定,比较分析戊二醛不同交联方式对复合膜机械性能稳定性、降解性及微观结构影响。结果表明,在3个月贮藏期内,戊二醛溶液交联改性、蒸汽交联改性处理复合膜拉伸强度稳定性提高了20.58%、38.51%,延伸率稳定性提高了31.71%、54.49%,水蒸气透过系数稳定性提高了31.74%、52.19%,透氧率稳定性提高了0.24%、18.01%,降解实验中降解速率分别为未经改性处理大豆蛋白基明胶复合膜溶液交联改性处理复合膜蒸汽交联改性处理复合膜。同时,蒸汽交联复合膜表面及拉伸断面形成结构致密的三维立体网络结构。因此,戊二醛蒸汽交联制备的大豆蛋白基明胶复合膜机械稳定性能及微观结构均优于戊二醛溶液交联改性处理复合膜。