Assessment of physical and mechanical properties of sodium caseinate and stearic acid based film-forming emulsions and edible films

Edible films were prepared using sodium caseinate (6–8 g/100 g) and stearic acid (0–2 g/100 g). Effects of the ratio of stearic acid and sodium caseinate to water on the water vapor permeability (WVP) and mechanical properties of the prepared films were evaluated. Film-forming emulsions were also tested for rheological properties and surface tension. Changes in the ratios of sodium caseinate and stearic acid to water had significant effects on WVP (p < 0.05) and surface tension (p < 0.01). Higher values of consistency coefficient and elastic modulus were obtained in the presence of higher stearic acid. In addition, increase in stearic acid content increased the rate of water loss and gain of elastic modulus at the early stage of drying and resulted in production of less flexible film. The resultant edible film prepared with 6 g/100 g sodium caseinate and 2 g/100 g stearic acid showed the lowest WVP of 1.368 (g mm/m² h kPa).     

Preparation and characterization of composite sodium caseinate edible films incorporating naturally emulsified oil bodies

Oil bodies in the form of a naturally emulsified emulsion were recovered from maize germ by applying aqueous extraction and were then exploited in the preparation of composite sodium caseinate-based films. Following equilibration of the initial film-forming dispersion, the caseinate molecules appeared to adsorb to the oil droplet surface facilitating thus the dispersion of the latter in the protein solution. During the course of film formation partial destabilization of oil body dispersion took place as a result of depletion by non-adsorbed caseinate. The finally formed composite films differed from the control, both in their surface characteristics as well in physicochemical and tensile properties. The oil-incorporating films were less transparent, less hydrophilic and, as a result, more resistant to water sorption and vapor permeation than the oil-free caseinate films. In addition, the composite films exhibited higher flexibility and lower stiffness. These findings are discussed in terms of the formation during the drying step of a composite caseinate-based phase separated structure embedded with oil bodies having their surface in intimate association with the protein molecules of the continuous protein matrix.     

Water vapour barrier and tensile properties of composite caseinate-pullulan films: Biopolymer composition effects and impact of beeswax lamination

The water sorption, water barrier properties and mechanical behaviour of pullulan (P) and sodium caseinate (SC), as well as their blend and bilayer films plasticized with sorbitol (25% dry basis), were investigated as a function of weight polymer ratio, water content and beeswax lamination. Very similar moisture sorption isotherms were obtained for blend and bilayer films with P/SC weight ratio of 1/3 and 3/1. Neither the type of film (blend or bilayer) nor the different P/SC ratio affected significantly (P > 0.05) the water vapour permeability (WVP) of the films. A mixture-process variable experimental design was applied to evaluate the effect of the proportion of the two polymers in relation with the relative humidity (RH, 53% and 75%) on the mechanical properties of the films. Increasing the P/SC ratio decreased the Young’s modulus (E), the tensile strength (σ_max) and increased the % elongation at break (% EB), suggesting that P imparts flexibility and SC stiffness to the composite films. With moisture content increase from 5% to 8% most of the films exhibited an increase in E and σ_max, whereas a sharp decline in both parameters and an increase in % EB were observed above this moisture level. The brittle to ductile transition of P coincided with its glass to rubber transition, whereas SC exhibited a ductile behaviour within the glassy state. The tensile characteristics of bilayer films at moisture content greater than 8% were dominated by the component present in higher proportion, while films made with the biopolymer blends showed mechanical behaviour closer to that of plain P films. Beeswax lamination of plain, bilayer and blend films resulted in a drastic decrease in water vapour permeance, whereas its effect on E and σ_max and in % EB was related to the mechanical properties of the hydrocolloid layers used and varied according to the moisture content of the films.     

Antimicrobial, water vapour permeability, mechanical and thermal properties of casein based Zataraia multiflora Boiss. Extract containing film

Hydrophobic sodium caseinate based edible films were prepared by incorporating stearic and oleic acids. Films were produced with a protein/lipid ratio of 1.05. Antimicrobial films were produced based on the hydrophobic films by adding the essential oil of Zataraia multiflora Boiss. Water vapour permeability, microstructure, antimicrobial, mechanical and thermal properties of these films were studied. Water vapour permeability decreased from 2.18 × 10⁻⁹ to 7.81 × 10⁻¹¹ gPa⁻¹s⁻¹ m⁻¹ on the addition of lipid compounds to film. Scanning electron microscopy showed a partial phase separation of lipid compounds and protein. This fact was confirmed by obtaining two endothermic peaks for lipid containing films during Differential scanning calorimeter. The incorporation of fatty acids into the film structure increased the total specific thermal capacity. The presence of lipids and essential oil decreased tensile strength but increased the elongation at break. Films containing essential oil exhibited a large inhibitory effect on Staphylococcus aureus, as compared to Salmonella typhimurium and Escherichia coli O157:H7.     

Effect of rice wax on water vapour permeability and sorption properties of edible pullulan films

Edible films were prepared using various ratios of pullulan and rice wax. Freestanding composite films were obtained with up to 46.4% rice wax. Water vapour barrier properties of the pullulan film were improved with increased addition of rice wax. Moisture sorption isotherms were also studied to examine the impact of rice wax on the water sorption characteristics of the film. The Brunauer–Emmet–Teller (BET) and Guggenheim–Anderson–de Boer (GAB) sorption models were tested to fit the experimental data. The models gave a good fit up to the water activity (a_w) of 0.55 for BET and a full range of a_w from 0.12 to 0.95 for GAB (R² ? 0.98). Changes in the sorption parameters, particularly such as the decrease in monolayer moisture content (Mo), reflect the trend of reduced hydration capacity with increased addition of rice wax, providing useful information on water activity conditions to achieve stability for the composite films.     

Structure and mechanical properties of sodium and calcium caseinate edible active films with carvacrol

Edible active films based on sodium caseinate (SC) and calcium caseinate (CC) plasticized with glycerol (G) at three different concentrations and carvacrol (CRV) as active agent were prepared by solvent casting. Transparent films were obtained and their surfaces were analysed by optical microscopy and scanning electron microscopy (SEM). The influence of the addition of three different plasticizer concentrations was studied by determining tensile properties, while Fourier transformed infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were used to evaluate the structural and thermal behavior of such films. The addition of glycerol resulted in a reduction in the elastic modulus and tensile strength, while some increase in the elongation at break was observed. In general terms, SC films showed flexibility higher than the corresponding CC counterparts. In addition, the presence of carvacrol caused further improvements in ductile properties suggesting the presence of stronger interactions between the protein matrix and glycerol, as it was also observed in thermal degradation studies. FTIR spectra of all films showed the characteristic bands and peaks corresponding to proteins as well as to primary and secondary alcohols. In summary, the best results regarding mechanical and structural properties for caseinates-based films containing carvacrol were found for the formulations with high glycerol concentrations.     

Structure and properties of nanocomposite films based on sodium caseinate and nanocellulose fibers

Films made from sodium caseinate and nanocellulose were prepared by dispersing the fibrils into film forming solutions, casting and drying. Composite films were less transparent and had a more hydrophilic surface than neat sodium caseinate ones. However, the global moisture uptake was almost not affected by filler concentration. Addition of nanocellulose to the neat sodium caseinate films produced an initial increase in the barrier properties to water vapor, and then, it decreases as filler content increased. This was explained in terms of additional detrimental changes (cracks and bubble formation) induced in the morphological structure of the film by the reinforcement.The tensile modulus and strength of composite films increased significantly with increasing cellulose concentrations, while the values of elongation decreased. In the same way it was found that the storage modulus increases considerably with filler addition in the low temperature range (<60 °C), though the effect of temperature on the films performance is even more dramatic, as expected in protein-based materials.     

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.     

Mechanical, water vapor barrier and thermal properties of gelatin based edible films

Edible films are thin materials based on a biopolymer. The objectives of this work were to determine the water vapor permeability and the mechanical and thermal properties of edible films based on bovine hide and pigskin gelatins. These films were prepared with 1 g of gelatin/100 ml of water; 15–65 g sorbitol/100 g gelatin; and at natural pH. The samples were conditioned at 58% relative humidity and 22°C for 4 days before testing. The mechanical properties were determined by the puncture test and the water vapor permeability by gravimetric method at 22°C. For DSC analysis, samples were conditioned over silica gel for 3 weeks. Samples (10 mg) were heated at 5°C/min, between −150 and 150°C in a DSC TA 2010. A second scan was run after cell cooling with liquid nitrogen. As expected, the puncture force decreased and the puncture deformation and water vapor permeability increased with the sorbitol content. The origin of gelatin was important only above 25 g sorbitol/100 g gelatin. The DSC traces obtained in the first scan of samples with 15–35 g sorbitol/100 g gelatin, showed a well visible glass transition followed by a sol–gel transition. However, with the increase of sorbitol concentration, the glass transition became broader, typical of the system presenting a phase separation. The model of Couchman and Karazs for ternary system, was used to predict the Tg values as a function of sorbitol concentration.     

Mechanical and barrier properties of sodium caseinate–anhydrous milk fat edible films

Edible films were cast from solutions of sodium caseinate (NaCAS) and from emulsions of this protein with anhydrous milk fat (AMF). The moisture sorption isotherms, mechanical properties [tensile strength (TS) and elongation] and water vapour and oxygen permeabilities were determined for films based on NaCAS as a function of AMF concentration. AMF concentration significantly affected TS (P < 0.001) and elongation (P < 0.05). The increase of lipid content led to a loss of mechanical efficiency, but had little influence on water vapour barrier properties. No significant difference (P > 0.05) occurred between oxygen permeability of films at each lipid concentration.     

Influence of CaCl2 on the water vapor permeability and the surface morphology of mesquite gum based edible films

Oil-in-water (O/W) emulsions with a dispersed phase mass fraction (φ_m) of 0.175 were prepared by dispersing a blend of candelilla wax/mineral oil (2:1 ratio) in 10 g of mesquite gum per 100 g of water containing either CaCl₂ (0.0, 0.1, 0.2, 0.3, 0.4 or 0.5 g) alone or combined with 1.5 g of glycerol. The mean volumetric droplet size (d_3,0), the rate of droplet coalescence (C) and the viscosity-shear rate behavior of the emulsions were affected by the addition of CaCl₂ alone or combined with glycerol. The Carreau-Yasuda model fitted best the viscosity-shear rate data of all the emulsions. The surface morphology of the edible films, analyzed by Atomic Force Microscopy (AFM), exhibited a strong dependence on the CaCl₂ concentration. Maximum roughness occurred with a CaCl₂ concentration of 0.3 g per 100 g. Films with glycerol showed significantly higher roughness than those with only CaCl₂. Water vapor permeability (WVP) was significantly lowered as the concentration of CaCl₂ increased from 0.1 to 0.3 g per 100 g in the coatings, but increased again at CaCl₂ concentrations of 0.4-0.5 g per 100 g. Coatings containing glycerol displayed significant higher WVP.     

Properties of and mechanisms of protein interactions in films formed from different proportions of heated and unheated whey protein solutions

A range of films were formed using different proportions of heated (80°C for 30 min) and unheated whey protein isolate (WPI) solutions. The films, with lower proportions of heated WPI solution had lower percentage elongation, tensile strength and Young's modulus, higher solubility and, in general, similar water vapour permeability, compared with a film formed from a heated WPI solution. Hydrophobic interactions and hydrogen bonding dominated in the formation of the films with lower proportions of heated WPI solution, whereas disulphide bonding played a more important role in the formation of films with higher proportions of heated WPI solution.     

Effects of murta (Ugni molinae Turcz) extract on gas and water vapor permeability of carboxymethylcellulose-based edible films

The effect of murta (Ugni molinae Turcz) leaves extract on water vapor permeability (WVP) and gas permeability (GP) of carboxymethylcellulose (CMC)-based films was studied. Two ecotypes of murta leaves “Soloyo Grande” (SG) and “Soloyo Chico” (SC), were analyzed for their composition (HPLC-MS) and SC extract revealed a higher concentration of flavonols than the SG extract. The film forming solution was prepared with 2 g of CMC, 0.4 ml of glycerol and 0.5 ml of sunflower oil in 100 ml of water (Control), 50 ml of water and 50 ml of each exctract (SC50 or SG50) and 100 ml of each extract (SC 100 or SG 100). The addition of murta leaves extract modified the WVP and GP of the films. The WVP decreased significantly (P?0.05) with the incorporation of SG extract in the film but not with the SC extract (P>0.05). The CO₂ and O₂ permeability of the films were influenced by the kind and concentration of murta leaves extract used. The CO₂ permeability, with SG extract was higher than without extract (P?0.05) and with SC extract was not modified. The O₂ permeability with murta leaves extract were lower than without extract. Therefore, it is possible to consider that films with SC acts only as barrier to the oxygen, but with SG the water vapor and gas barrier properties were modified, being more permeable to the CO₂ and acting as barrier to O₂ and water vapor.     

Physical properties of edible emulsified films based on pistachio globulin protein and fatty acids

Novel edible composite films were prepared from pistachio globulin protein (PGP), saturated fatty acids, and an emulsifier using the emulsification technique. The water vapor permeability (WVP) of the emulsified films was reduced by approximately 37–43% by fatty acid addition. The effect of fatty acid on the oxygen permeability (OP) of PGP films was indirectly determined as the oil peroxide value. The OPs of the emulsified films were lower than those of a PGP film without fatty acid, but the differences were not significant (P < 0.05). The mechanical properties of PGP films were also affected by fatty acid addition; the ultimate tensile strength (UTS) was diminished, and elongation at breaking (E) decreased considerably (35–70%). Furthermore, the incorporation of fatty acid increased the opacity of the films. Finally, differential scanning calorimetry showed that the glass transition temperature (T_g) of the PGP film was ∼127 °C and was not considerably affected by fatty acid addition.     

Characterisation of composite films made of konjac glucomannan (KGM), carboxymethyl cellulose (CMC) and lipid

Emulsion films prepared from konjac glucomannan (KGM), carboxymethylcellulose (CMC), with and without alkali (KOH), were characterised for selected properties such as morphological characteristics, water vapour permeability (WVP), water sorptive capacity and tensile properties. It was found that smaller lipid globules, with a homogeneous distribution, increased the apparent hydrophobicity and “tortuosity” of an emulsion film for water molecule transmission, thereby resulting in reduced WVP. This was achieved when alkaline deacetylated KGM and CMC were served as the base polymers for the emulsion, with the latter functioning as an emulsifier. Interactions between deacetylated KGM and CMC resulted in a stable emulsion.     

Characterization and improvement of rheological properties of sodium caseinate glycated with galactose, lactose and dextran

The aim of this work was to investigate the effect of non-enzymatic glycosylation with galactose, lactose, and 10 kDa dextran on the rheological properties of sodium caseinate. To promote the formation of covalent complexes, the reaction was done in solid state (a_w = 0.67), pH 7.0 (0.1 M sodium phosphate buffer), and temperature set at 50 and 60 °C. The progress of Maillard reaction was indirectly traced by measuring the formation of the Amadori compound, through furosine (2-furoylmethyl-lysine) analysis, and brown polymers, and the resulting glycoconjugates were characterized by LC/ESI-MS and SEC. Results showed a higher reactivity of galactose than lactose and dextran to form the glycoconjugates, due to its smaller molecular weight. Glycation with galactose and lactose increased the viscosity of caseinate and also altered its flow characteristics from Newtonian to shear-thinning. Oscillatory testing showed a higher elastic modulus (G′) in glycoconjugates when compared to non-glycated caseinate, especially with galactose, where a gel-like behaviour was observed after long incubation times. Glycation with dextran did not produce substantial improvements in the rheological properties of caseinate, probably due to the limited extent of the reaction. Our results show that by controlling the rate and extent of the Maillard reaction is a technologically feasible operation to improve the viscosity and gelling properties of sodium caseinate-based ingredients.     

Hake proteins edible films incorporated with essential oils: Physical,mechanical, antioxidant and antibacterial properties

Physical, mechanical, antioxidant and antimicrobial properties of hake protein films incorporated with citronella, coriander, tarragon and thyme oils were investigated. Dried hake proteins were solubilized at pH 11.0 (protein concentration in film forming solution ca. 0.9%) and glycerol (59% w/w of protein) and 0.25 ml of each essential oil per gram of protein was added. Films obtained were homogeneous and transparent with a yellowish colour. The addition of the different essential oils reduced the water vapour permeability but increased the solubility of films in water. The amount of protein released from the films depended on the oil added. Among all essential oils incorporated-films the thyme oil films exhibited the lowest mechanical properties (puncture force and elongation at break). Conversely, films with thyme oil added presented the highest inhibition against Shewanella putrefaciens. Antioxidant activity of hake protein films generally increased with the incorporation of essential oils as indicated by DPPH radical scavenging activity and reducing power.     

Effect of added calcium chloride on the physicochemical and rheological properties of aqueous mixtures of sodium caseinate/sodium alginate and respective oil-in-water emulsions

Changes induced by addition of calcium chloride in particle size distribution and electrokinetic potential were determined in sodium caseinate/sodium alginate mixtures dissolved in water or acetate buffer at ambient temperature. Rheological properties of aqueous mixtures and respective oil-in-water emulsions (30% oil w/w) were evaluated using a low-stress rheometer. Stability and particle diameter of emulsions were measured. Caseinate and alginate solutions were negatively charged and showed negative electrokinetic potential; however values of mixtures were between those of the values for the individual hydrocolloids. When calcium ions were added the electrokinetic potential diminished while the negative charge was preserved. Aqueous mixtures of caseinate and alginate showed average particles size between of those of caseinate or alginate samples. We observed low viscosity values and Newtonian behavior for both caseinate (1 and 2%) and alginate (0.1%). Addition of 5 mM CaCl₂ to alginate solutions induced shear-thinning behavior as well as the development of viscoelasticity. Both the viscosity and the elastic modulus of these polysaccharide solutions were attenuated by the presence of protein or dispersed oil in mixtures or emulsions, respectively. High average particle diameter of emulsions prepared was obtained (close to 10 μm), however, stability of emulsions was possible only with the addition of CaCl₂ to the mixtures, in both water and acetate buffer. In these cases elastic behavior predominated to viscosity in the formation of emulsions, confirming the prevalence of aqueous phase rheology on emulsions.     

Edible composite films of wheat gluten and lipids: water vapour permeability and other physical properties

Edible composite films comprised of wheat gluten as the structural matrix and various concentrations of different lipids as the moisture barrier component were tested for water vapour permeability, dispersion in water, opacity and mechanical properties. the effects of lipids on the functional properties of gluten-based composite films depended on the lipid characteristics and on the interactions between the lipid and the protein structural matrix. Beeswax, a solid and highly hydrophobic lipid, was the most effective lipid for improving moisture barrier properties of films; but these films were opaque, weak and disintegrated easily in water. Combining wheat gluten proteins with a diacetyl tartaric ester of monoglycerides reduced water vapour permeability, increased strength and maintained transparency.     

Influence of hydrocolloid nature on the structure and functional properties of emulsified edible films

To investigate the influence of polymer behaviors on the structure and the functional properties of emulsified films, agar (AG) and cassava starch (CAS) were used as hydrocolloid continuous phases in which hydrogenated vegetable oil (VGB81) was dispersed. Different ratios of hydrophilic/hydrophobic materials (HB/HL) were also used in film formulations to study the evolution of film-emulsion structure. Microscopically observed, VGB–CAS emulsified films exhibit a similar bilayer structure. However, there was just a migration and an aggregation of lipid particles. There was no coalescence which could form a continuous “lipid layer” necessary for an effective barrier. Moreover, they could not be made with a HB/HL ratio greater than 0.7:1. Conversely, AG chains set into gel, which solidifies film-forming emulsion before drying, leading to a fixed macronetwork structure. Films made with a high HB/HL ratios lead to a film structure becoming like a multilayer system. The water vapor permeability of emulsified films is better found when HB/HL ≥ 1:1 when films are formed only with gelling polysaccharide (AG). In addition, there is no relationship between the moisture sorption and the moisture permeability of emulsified films. In contact with liquid water, brief sorption and swelling surface are observed for VGB–AG film surface and rapid absorption following a temporary hydrophobicity is found in the case of VGB–CAS films. While the mechanical properties of VGB–CAS films are strongly altered, those of VGB–AG films are considered to be sufficient for most of applications.