Influence of calcium on tensile, optical and water vapour permeability properties of sodium caseinate edible films

The influence of calcium on sodium caseinate edible films with and without lipid addition (oleic acid (OA)–beeswax (BW) mixtures) was investigated through the analysis of tensile, optical and water vapour barrier properties. Calcium was added by substitution of sodium caseinate by calcium caseinate. Calcium caseinate films have less transparency and more rigidity but they have lower water vapour permeability values than sodium caseinate films. The effect of substitution was different for films with and without lipids. Calcium caseinate increased tensile strength and decreased elongation of films, depending on the level of substitution and lipid presence. Among control films (without lipid), water vapour permeability was reduced when calcium caseinate was present, reaching values of 3.9 (±0.2) g mm kPa⁻¹ h⁻¹ m⁻². Nevertheless, in the films containing lipids, this reduction was inhibited when the level of sodium caseinate substitution exceeded 50%. Film transparency and gloss was reduced by calcium caseinate and lipid presence, although pure calcium caseinate films were glossier. When taking all the studied variables into account, the films prepared with 2:1 NaCas:CaCas ratio and 70:30 OA:BW ratio showed the most adequate properties.     

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).     

Characterization of sodium caseinate-based edible films incorporated with cinnamon or ginger essential oils

Film-forming emulsions were formulated with sodium caseinate and two essential oils (cinnamon or ginger) and films were obtained by casting. At the low oil proportion being tested (maximum ratio protein:oil 1:0.100), the lipid did not affect the mechanical behaviour of the protein films. The water vapour permeability was slightly reduced by both oils. Cinnamon oil greatly affected the optical properties of the films. Ginger oil resulted in lipid droplet aggregation observable by Scanning Electron Microscopy in dried films, surface irregularities and gloss decrease. Neither of the oils improved the ability of sodium caseinate films to act as protection against lipid oxidation, despite the fact that, in a spectrophotometric method, isolated cinnamon oil proved to be very a strong antioxidant.     

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.     

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.     

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.     

Potato starch edible films to control oxidative rancidity of polyunsaturated lipids: effects of film composition, thickness and water activity

The objective of this work was to study the effect of potato starch-based films acting as oxygen barrier on the oxidative rancidity of vegetable oil, as an example of a food rich in polyunsaturated fatty acids. The effect of glycerol (Gly) content (0%, 10%, 20%, 30%), film thickness (30, 60, 100 μm) as well as environmental relative humidity (RH) (50% or 75%) were analysed. Results obtained confirmed that potato starch films delayed the rancidity in vegetable oil. Films without Gly provided the same protection as films with 10% Gly. Films with higher Gly content were not as effective oxygen barrier. It is likely that the fact that film protective capability diminished with increased RH or Gly content was due to the increasing moisture content of the films. Despite that fact, potato starch films can be considered a very efficient oxygen barrier even at RH as high as 75%.     

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.     

Diffusion of small molecules in edible films: Effect of water and interactions between diffusant and biopolymer

Mass transfers of various molecules in multiphasic food products lead to quality modification and thus require the use of edible films or coatings in-between the foodstuff. Consequently, it is important to assess the barrier properties and efficiencies of edible films as well as to determine the diffusivities of the migrants. Translational diffusion of a reference molecule such as fluorescein, determined by the fluorescence recovery after photobleaching (FRAP) method, displays a threshold of a critical water content inducing an increase of the molecular mobility, and demonstrates that multiple populations of a single molecular specie can be involved in different diffusion kinetics. Further investigations at a molecular scale through high resolution solid state nuclear magnetic resonance (NMR) enables to go deeper into the understanding of the interactions involved in such a system, in particular on the identification of the possible binding sites of the diffusant on the polymer and on the overall effect of interactions on the polymer organization. Therefore, the appraisal of transport properties in foods by means of reference molecules constitutes a relevant approach to use in combination with molecular investigation of physicochemical interactions with the diffusing substances.     

Effect of pH on the formation of edible films made from the muscle proteins of Blue marlin (Makaira mazara)

Whole meat of Blue marlin (Makaira mazara) was used to prepare edible films. Protein solubility in film-forming solutions was high at acidic and alkaline pHs, while that at neutral pH was close to zero. Acidic and alkaline pHs improved the tensile strength while the effects of pH, on elongation at break, water vapour permeability and light transmission of the films, were not significant. From the film solubility in various protein denaturants it was revealed that the main interaction responsible for the formation of acidic and alkaline pH films was hydrophobic interaction, while that for neutral pH films was ionic bonding.     

Stability of the mechanical properties of edible films based on whey protein isolate during storage at different relative humidity

Formulations for whey protein isolate (WPI)-based films include low molecular weight plasticizers, which implies certain degree of instability of films properties due to plasticizer migration. The aim of this work was to study the effect of storage time on the mechanical properties of WPI films plasticized with two low molecular weight polyols: glycerol (Gly) and sorbitol (Sor). Films were stored inside cabins at 50% or 75% relative humidity (RH) and at room temperature. Mechanical properties and moisture content were measured at regular intervals for 30 weeks. The effect of plasticizer type and content and RH on mechanical properties right after equilibrium (1 week) was also included in this study.     

Use of transient and steady-state methods and AFM technique for investigating the water transfer through starch-based films

The aim of this study was to investigate the water transfer properties of starch films using steady-state and transient methods and to evaluate the influence of air relative humidity on the film roughness using atomic force microscopy (AFM). Films were prepared with 3% starch and 0.3 g glycerol/g dry starch. Composite-films were prepared with the addition of 0.3 g cellulose/g dry starch. Water transfer through the films exhibited a dependence on the relative humidity RH. Using AFM, film roughness was observed to increase from a few nanometers to 45 nm over 1.5 h when the films were exposed to high RH. Results indicated that the equilibrium conditions at the film surface were not reliable boundary conditions and that the diffusion coefficients determined by both transient and steady-state methods may be different because they were determined at different conditions. Further studies of water permeability, assisted by AFM, could be performed for a better understanding of film barrier properties.     

保水剂及冷风干燥对鱼糜溶胶水分状态的影响研究

目的:探讨保水剂及冷风干燥对鱼糜溶胶水分状态的影响。方法:将鱼糜中添加不同保水剂制成溶胶,经冷风干燥一定时间后进行高温处理,测量冷风干燥不同时间后水分含量、水分活度和水分状态的变化,通过5分法评分标准评定鱼糜溶胶高温处理后的凝胶特性。结果:随着冷风干燥时间的延长,空白组及添加保水剂组的鱼糜溶胶的水分含量均呈现下降趋势,添加保水剂组的水分含量降低速率均小于空白组;水分活度也呈现一定的下降趋势,添加保水剂可显著降低鱼糜溶胶的水分活度,弛豫时间T21和T22明显向低的弛豫时间方向迁移,鱼糜溶胶中的结合水和自由水含量随冷风干燥时间的延长均呈现上升趋势,而不易流动水呈现下降趋势,另外,鱼糜溶胶高温处理后的凝胶特性呈现上升的趋势。结论:降低水分含量可有效提高鱼糜溶胶高温处理后的凝胶特性,同时可通过添加保水剂改变水分活度和水分状态从而进一步提高鱼糜溶胶的高温处理热稳定性。      

Biopolymer interactions affect the functional properties of edible films based on agar, cassava starch and arabinoxylan blends

Edible films based on the binary combination of agar (AG), cassava starch (CAS) and arabinoxylan (AX) were studied with regard to their microstructure, moisture barrier and mechanical properties. Though the films appear macroscopically homogeneous, electron microscopy observations reveal a phase separation and dispersion, respectively, in AG–CAS and AG–AX blend film structures, whereas the structure of CAS–AX blend films seems homogeneous. In case high moisture (84% and 99% RH), neither the combination of AG and CAS nor the addition of AX into CAS can improve film moisture barrier properties, except at a lower RH (57%). Conversely, water vapor permeability (WVP) of AG based film is significantly reduced when AX is used as an “additive”. On the other hand, blending AG with CAS increases the surface wettability of AG films but not that of CAS films. Adding AG into CAS induces an improvement in elongation and tensile strength of CAS based films. Mechanical properties of agar based films are degraded when CAS or AX was added. The results suggest that AG is able to provide a very good cohesive matrix, which contributes to enhance the mechanical properties of other polysaccharide based films.     

The effects of ultrasonic/microwave assisted treatment on the properties of soy protein isolate/titanium dioxide films

Soy protein isolate (SPI, 5.0 g/100 mL,) films embedded with nano-TiO₂ (0, 0.5, 1.0, 1.5 and 2.0 g/100 mL) were prepared by solution casting and modified by ultrasonic/microwave assisted treatment (UMAT). The effects of nano-TiO₂ content and UMAT time on the films' physical properties and structure were investigated. Incorporation of nano-TiO₂ significantly enhanced films' mechanical properties and barrier properties, because of the intermolecular force between nano-TiO₂ and SPI. UMAT time ≤20 min obviously improved films' tensile strength values (15.77 MPa, 245% higher than the control), and reduced water vapor permeability (1.8457 × 10⁻¹¹ g cm⁻¹ s⁻¹ Pa⁻¹, 72.11% lower than the control) and oxygen permeability values (0.8897 × 10⁻⁵ cm³ m⁻² d⁻¹ Pa⁻¹, 57.66% lower than the control). SEM images also revealed a more compact and dense structure of films when UMAT time ≤20 min. Films' water adsorption properties were evaluated. GAB and Henderson models exhibited the best to fit experimental data, thus it was predicted that films (1.5 g nano-TiO₂/100 ml) could be stable at low moisture content (0.27 kg of water/kg dry mass).     

Analysis of free and esterified sterols in edible oils by online reversed phase liquid chromatography-gas chromatography (RPLC-GC) using the through oven transfer adsorption desorption (TOTAD) interface

An online reversed phase liquid chromatography-gas chromatography (RPLC-GC) method is proposed to quantify free, total and esterified sterols of edible oils. To determine free sterols the diluted oils are injected into the liquid chromatograph, where free sterols are separated from triglycerides and the sterol fraction is automatically transferred to the gas chromatograph to be analysed. To determine total sterols the samples were saponified with potassium hydroxide in ethanolic solution and the unsaponifiable fraction was extracted with diethyl ether. The extract was then analysed by RPLC-GC, avoiding the laborious thin layer chromatography step used in the Official European Union (EU) Method. The relative standard deviations (RSDs) from the absolute peak area varied from 7.6% to 15.8%. Limits of detection (LODs) were less than 8.5 mg/kg. No variability in retention time was observed. The method was applied to the determination of total sterols in edible oil samples and the results were compared with those obtained with the Official EU Method. Good agreement was found between both methods, except in the case of campesterol.     

The effect of edible coatings and polymeric packaging films on the quality of minimally processed carrots

Minimally processed carrots have a short shelf‐life because of white blush formation (caused primarily by surface dehydration) and microbiological spoilage (caused mostly by lactic acid bacteria). The use of polymeric packaging films combined with edible coatings might have an additive or synergistic effect to extend the shelf‐life of minimally processed carrots because of the formation of a double barrier to gases and water vapour. A 3 × 3 factorial experiment using a polymeric packaging film of three different levels of permeability and a cellulose‐based edible coating (Nature Seal^®) at different concentrations was conducted on minimally processed carrots to investigate any possible synergistic effect over 12 days of storage at 10 °C. No such effect was found. The polymeric packaging film effectively prevented microbiological growth and spoilage but was unable to control white blush formation. On the other hand, the edible coating partially controlled white blush formation but enhanced microbiological spoilage. The polymeric packaging film functioned primarily as a gas barrier, whereas the edible coating probably functioned as a moisture barrier. White blush formation was found to be the most important shelf‐life determinant for minimally processed carrots. Copyright © 2003 Society of Chemical Industry     

Development of a novel bioactive packaging based on the incorporation of Lactobacillus sakei into sodium-caseinate films for controlling Listeria monocytogenes in foods

A novel packaging technology was developed based on the incorporation of Lactobacillus sakei cells into sodium-caseinate (SC) edible films. Incorporation was based either on direct addition of the cells in the film forming solution used for casting or by surface spraying of the culture on the preformed film, resulting in a population density of 10⁶ cfu/cm². Addition of sorbitol in the film matrix increased the viability of the cells, greater than 90%, upon storage under both refrigeration and ambient temperature conditions for 30 days. Incorporation of the viable protective culture did not affect the mechanical properties and the physico-chemical properties of the film. Application of the films to both laboratory medium (agar) and a food model system (fresh beef) inoculated with Listeria monocytogenes resulted in a rapid growth of L. sakei immobilized in the film following contact with the wet medium or the food surface and a significant inhibition of the pathogen growth compared to the control samples under both constant and dynamic storage temperature protocols. The present study indicated that biopolymer-based antimicrobial films containing cells of a protective culture can be used as an effective packaging technology for improving food safety.     

The influence of hydrophobic substances on water vapor permeability of fish gelatin films modified with transglutaminase or 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)

The effect of different hydrophobic substances on water vapor permeability (WVP) of unmodified fish gelatin films and cross-linked with transglutaminase (TGase) or with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) was determined. Both unmodified and cross-linked films were characterized by very poor water barrier properties. Amaranth oil, rapeseed oil, lanolin, beeswax and ozococerite at concentration of 10% decreased WVP of unmodified gelatin films by 42, 15, 37, 53 and 36%, respectively. Increasing concentration of these substances up to 60% caused further improving of the water barrier properties. Addition of lecithin into film-forming emulsions prevented separation of lipid layer on the film surface. Among unmodified films with lecithin and 60% of lipids the highest decrease of WVP was found in case of amaranth oil and beeswax, by 73 and 87%, respectively, in comparison to only-gelatin films. WVP of chemically modified films in the presence of 60% of beeswax with addition of lecithin was decreased by about 65%. Enzymatically modified films with beeswax were very brittle and broke during analyzes, similarly as those with amaranth oil and lecithin. WVP of enzymatically modified films with lecithin and 60% of rapeseed oil and lanolin was respectively, about 60 and 47% lower than that of films without hydrophobic substances.     

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.