Water barrier and physical properties of starch/decolorized hsian-tsao leaf gum films: Impact of surfactant lamination

The moisture barrier and physical properties of bilayer films prepared by lamination of starch/decolorized hsian-tsao leaf gum (dHG) and surfactant layers were investigated. It was found that the water vapor permeability (WVP) of tapioca starch/dHG film (1.31 × 10^?10 g/m s Pa) pronouncedly decreased by the aid of a surfactant layer lamination (1.36–5.25 × 10^?12 g/m s Pa). The WVP of bilayer film increased with increasing the concentration of starch/dHG in the surfactant layer, but was not significantly influenced when it was thickened. The sorption isotherms of both monolayer and bilayer films made from starch/dHG showed typical behavior of water-vapor-sensitive hydrophilic biopolymers. However, the equilibrium moisture content of the monolayer film was significantly higher than that of bilayer films when water activity (a_w) reaches 0.33. Both the tensile and puncture force of starch/dHG films did not vary significantly by laminating a surfactant layer, indicating the mechanical strength of surfactant layer is relatively weak, and this surfactant layer mainly served as a barrier for moisture. When compared to emulsion-based starch/dHG films with surfactant, the surfactant laminated starch/dHG films showed higher water barrier property, mechanical strength, and transparency.     

Physico-chemical properties of whey protein isolate films containing oregano oil and their antimicrobial action against spoilage flora of fresh beef

Antimicrobial films were prepared by incorporating different levels of oregano oil (0.5%, 1.0%, and 1.5% w/w in the film forming solution) into sorbitol-plasticized whey protein isolate (WPI) films. The moisture uptake behavior and the water vapor permeability (WVP) were not affected by the addition of oregano oil at any of the concentrations used. A reduction of the glass transition temperature (∼10–20 °C), as determined by dynamic mechanical thermal analysis (DMTA), was caused by addition of oil into the protein matrix. A decrease of Young modulus (E) and maximum tensile strength (σ_max) accompanied with an increase in elongation at break (%EB) was observed with increasing oil concentration up to a level of 1.0% (w/w). Wrapping of beef cuts with the antimicrobial films resulted in smaller changes in total color difference (ΔΕ) and saturation difference (Δ_chroma) during refrigeration (5 °C, 12 days). The maximum specific growth rate (μ_max) of total flora (total viable count, TVC) and pseudomonads were significantly reduced (P < 0.05) by a factor of two with the use of antimicrobial films (1.5% w/w oil in the film forming solution), while the growth of lactic acid bacteria was completely inhibited. These results pointed to the effectiveness of oregano oil containing whey protein films to increase the shelf life of fresh beef.     

Effects of lipids on mechanical and moisture barrier properties of edible gellan film

Beeswax or a 1:1 blend of stearic–palmitic acids (S–P) were incorporated into gellan films through emulsification to form gellan/lipid composite films. The films, containing 0–25% lipid (dry film basis) were examined for mechanical properties, water vapor permeability (WVP) and opacity. Addition of the lipids to gellan films significantly improved the WVP (P<0.05), but lowered the mechanical properties and caused the films to become opaque. Beeswax was more effective than S–P acids in reducing the WVP, and films with beeswax showed better mechanical properties overall than those with S–P acids. The tensile properties of gellan films containing 14.3% beeswax were evaluated as a function of water activity (a_w) of the film. Increasing the a_w decreased the tensile strength (TS) and elastic modulus but tensile elongation was not affected. The extent of the decreases in TS for the composite film was less pronounced than that for a similar film without lipids, suggesting that lipids help to alleviate moisture sensitivity of gellan films.     

Physicochemical properties and application of pullulan edible films and coatings in fruit preservation

The effects of water, sorbitol and a sucrose fatty acid ester (SE) on the water sorption behaviour and thermal and mechanical properties of pullulan‐based edible films as well as the physiological responses of fruit coated with pullulan have been studied. Incorporation of sorbitol or SE in pullulan films resulted in lower equilibrium moisture contents at low to intermediate water activities (a_w), but much higher moisture contents at a_w > 0.75; estimates of monolayer values (within 4.1–5.9 gH₂O kg^?1 solids) were given by application of the Brunauer–Emmett–Teller (BET) and Guggenheim–Anderson–DeBoer (GAB) models. A single glass–rubber transition (T_g), attributed to the polysaccharide component, was detected by calorimetry and dynamic mechanical thermal analysis (DMTA) at a sorbitol level of 15–30% DM. With both tests the strong plasticising action of water and polyol was evident in the thermal curves, and the T_g vs moisture content data were successfully fitted to the Gordon–Taylor empirical model. Multifrequency DMTA measurements provided estimates for the apparent activation energy of the glass transition in the range of ? 300–488 kJ mol^?1. With large‐deformation mechanical testing, large decreases in Young's moduli (tensile and three‐point bend tests) were observed as a result of water‐ and/or polyol‐mediated glass‐to‐rubber transition of the polymeric films. In the moisture content range of 2–8%, increases in flexural modulus (E) and maximum stress (σ_max) with small increases in moisture content were found for films made of pullulan or pullulan mixed with 15% DM sorbitol; a strong softening effect was observed when the water content exceeded this range. Addition of sorbitol increased the water vapour transmission rate of the films, whereas addition of SE had the opposite effect. Application of a pullulan/sorbitol/SE coating on strawberries resulted in large changes in internal fruit atmosphere composition which were beneficial for extending the shelf‐life of this fruit; the coated fruit showed much higher levels of CO₂, a large reduction in internal O₂, better firmness and colour retention and a reduced rate of weight loss. In contrast, similar studies on whole kiwifruits showed increased levels of internal ethylene, which caused acceleration of fruit ripening during storage. © 2001 Society of Chemical Industry     

Physical and Antimicrobial Properties of Tapioca Starch-HPMC Edible Films Incorporated with Nisin and/or Potassium Sorbate

The antimicrobial effectiveness of nisin and potassium sorbate, incorporated individual and combined, in films made with tapioca starch and its mixtures with hydroxypropyl methylcellulose were studied. The combination of antimicrobials was more effective against Listeria innocua and Zygosaccharomyces bailii than their individual incorporation, with the added advantage of providing greater inhibitory spectrum. The effect of the formulation on some physical properties was also evaluated. The blended biopolymers-based films showed an increase of stress (σ _r) and elastic modulus (E) but a decrease of the strain at break (ε _r). In turn, the water vapour permeability and solubility in water were enhanced. In addition, these films were clearer than those made only with starch. It must be remark that, despite the antimicrobial agents modified films physical properties, producing a lower σ _r and E, a higher ε _r, solubility and darker films, they maintained a suitable behaviour as a packaging material.     

Biopolymer-based films as carriers of antimicrobial agents

Films were prepared by incorporating different levels of antibacterial agents such as oregano oil, sodium lactate (NaL) and ɛ-polylysine (ɛ-PL) into sorbitol-plasticized whey protein isolate (WPI) films. The moisture uptake behaviour and the water vapour permeability (WVP) of the films were only affected by NaL, as the water sorption and permeability increased with addition of NaL into the protein matrix. An increase of the glass transition temperature of the sorbitol regions, as assessed by Dynamic Mechanical Thermal Analysis (DMTA), was caused by the addition of ɛ-PL, while incorporation of the oregano oil caused plasticization of the film that was depicted by a decrease in the transition temperature of the polymer-rich regions. On the other hand, incorporation of NaL into the films did not significantly alter their thermo-mechanical properties. However, the addition of NaL or ɛ-PL in the film forming solution resulted in a decline of maximum tensile strength (σ_max). Wrapping of beef cuts with the antimicrobial films resulted in a significant reduction of the bacterial population levels. The maximum specific growth rate (μ_max) of total flora (Total Viable Count, TVC) and pseudomonads was significantly reduced (P<0.05), with the use of antimicrobial films containing relatively high levels of oregano oil (1.5% w/w in the film forming solution) or ɛ-PL (0.75% w/w in the film forming solution), while the growth of Lactic Acid Bacteria (LAB) was completely inhibited.     

Properties of Laminated Films from Whey Powder and Sodium Caseinate Mixtures and Zein Layers

Corn zein-stearic acid films were laminated to whey powder (WP) and sodium caseinate (SC) mixture (WSM) films. WSM films were prepared at three mass ratios of WP and SC (50:50, 60:40, and 70:30 in w/w) by casting method. WSM films with poor mechanical and barrier properties were produced as the whey powder ratio of WSM increased from 50:50 to 70:30. Corn-zein lamination improved the mechanical and water barrier properties of WSM films by increasing tensile strength (TS) from 4.7-14.5 to 14.0-26.8 MPa and by decreasing water vapor permeabilities (WVP) from 0.432-0.490 to 0.386-0.422 ng m/m² s Pa. However, elongations of corn-zein laminated films were reduced from 64.5-128.0 to 2.6-4.5%. Mechanical and water barrier properties of corn-zein laminated WSM films were affected by the mass ratio of whey powder to sodium caseinate in WSM films. Addition of stearic acid up to 10 g/100 g of corn zein decreased TS and WVP of laminated films to approximately 12 MPa and 0.36 ng m/m² s Pa regardless of mass ratio in WSM film. However, no significant differences in TS and WVP were found with further addition of stearic acids.     

Phase transitions in starch based films containing fatty acids. Effect on water sorption and mechanical behaviour

The water sorption capacity (WSC) of starch films containing, or not, glycerol (1:0.25 starch:glycerol ratio) and fatty (palmitic, stearic and oleic) acids (1:0.15 starch:fatty acid ratio) was analysed at 10, 25 and 40 °C in the entire range of a_w. Starch re-crystallization during the equilibration time was also analysed by X-ray diffraction. Likewise, the glass transition and lipid melting properties as a function of the film water activity were determined. Mechanical behaviour was also analysed at 25 °C for film samples equilibrated at 0, 53, 68 and 75% RH. Crystallization was promoted at low temperature and high relative humidity which modifies the expected tendencies in WSC as a function of the temperature. In relationship with this, V-type structures were formed during time, mainly in fatty acids containing films. Glass transition of the starch matrix at low moisture contents was affected by the presence of saturated fatty acids. Microstructural observations seem to corroborate the complex formation between these and the polymer chains. The mechanical behaviour of the films, as a function of the moisture content, is coherent with the results of the phase transition analysis and microstructural observations. The plasticization effects and the structural discontinuities in the polymer matrices determine the value of the elastic modulus and the behaviour at break.     

Mechanical and Structural Properties of Expanded Extrudates Produced from Blends of Native Starches and Natural Fibers of Henequen and Coconut

The aim of this research was to evaluate the effects of barrel temperature (130‐180ºC), feed moisture (14.6‐24.5%) and fiber content (0.0‐15.0%) on the physicochemical and structural properties of starch‐derived loose‐fill packaging materials (LFPM). Two blends were analyzed: one of corn starch and henequen fiber (Agave americana) (CS‐HF), and the other of potato starch and coconut fiber (PS‐CF). An experimental laboratory extruder with a 2.9 mm internal diameter die‐nozzle was used, and a hybrid central composite design was employed to study the LFPM, and the influence of some extrusion variables on mechanical properties, i.e. tensile strength (ϵ),stress (σ), flexion modulus (E_f), and structural properties; expansion index (EI), water absorption capacity (WAC), crystallinity by X‐ray diffraction, viscosity profiles and scanning electronic microscopy (SEM). In both extruded blends feed moisture was the most significant variable, increasing the values of EI and ϵ, and decreasing the values of σ and E_f when the feed moisture was decreased. The blend of PS‐CF had the highest values of EI, ϵ, σ and E_f,, and is the more appropriate for the preparation of LFPM. X‐ray diffraction analysis of the LFPM samples suggested the formation of almost completely amorphous structures, similar to those of commercial LFPM prepared from polystyrene. This research indicated that blends from natural sources like corn starch with henequen, and potato starch with coconut fibers have the potential to be used in the preparation of LFPM with similar characteristics to commercial LFPM, with the additional advantage of being biodegradable.     

Preparation and properties of rice starch–chitosan blend biodegradable film

Biodegradable blend films from rice starch–chitosan were developed by casting film-solution on leveled trays. The influence of the ratio of starch and chitosan (2:1, 1.5:1, 1:1, and 0.5:1) on the mechanical properties, water barrier properties, and miscibility of biodegradable blend films was investigated. The biodegradable blend film from rice starch–chitosan showed an increase in tensile strength (TS), water vapor permeability (WVP), lighter color and yellowness and a decreasing elongation at the break (E), and film solubility (FS) after incorporation of chitosan. The introduction of chitosan increased the crystalline peak structure of starch film; however, too high chitosan concentration yielded phase separation between starch and chitosan. The amino group band of the chitosan molecule in the FTIR spectrum shifted from 1541.15 cm⁻¹ in the chitosan film to 1621.96 cm⁻¹ in the biodegradable blend films. These results pointed out that there was a molecular miscibility between these two components. The properties of rice starch–chitosan biodegradable blend film and selected biopolymer and synthetic polymer films were compared; the results demonstrated that rice starch–chitosan biodegradable blend film had mechanical properties similar to the other chitosan films. However, the water vapor permeability of rice starch–chitosan biodegradable blend film was characterized by relatively lower water vapor permeability than chitosan films but higher than polyolefin.     

Physical and mechanical properties of water resistant sodium alginate films

Properties of sodium alginate films were modified using two different methods of CaCl₂ treatment, i.e. the direct addition of CaCl₂ into film making solution (mixing films) and the immersion of alginate films into CaCl₂ solutions (immersion films), and their treatment effects on tensile strength (TS), percentage elongation at break (E), water vapor permeability (WVP), and water solubility (WS) of the films were investigated. TS and E of the mixing films were not changed considerably, but those of the immersion films changed considerably with significant (P<0.05) increase in TS and decrease in E. WVP of the immersion films decreased significantly (P<0.05), but that of the mixing films did not decreased. Water resistance measured by WS was not improved with the mixing films, but the alginate films became water resistant when they treated by immersing in higher than 2 g/100 ml CaCl₂ solutions. Water adsorption by the films also decreased in the immersion films. Swelling ratio (SR) of the immersion film decreased with temperature without affecting WS of the 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.     

Synergistic effects between κ-carrageenan and locust bean gum on physicochemical properties of edible films made thereof

The development of mixed systems, formed by locust bean gum (LBG), and κ-carrageenan (κ-car) can offer new interesting applications such as the development of edible films with particular properties. κ-car/LBG blend films with different ratios were developed, and their effects on films’ physical properties were assessed. Thermogravimetric analysis (TGA), X-ray diffraction (XRD) patterns, dynamic mechanical analysis (DMA) and Fourier-transform infrared (FTIR) spectroscopy techniques were used to highlight the interactions between the two polysaccharides. The addition of κ-car to LBG improved the barrier properties of the films leading to a decrease of water vapor permeability (WVP). Improved values of elongation-at-break (EB) were registered when the ratio of κ-car/LBG was 80/20 or 40/60 (% w/w). Moreover, the κ-car/LBG blend films enhance the tensile strength (TS) compared to κ-car and LBG films. FTIR results suggested that hydrogen bonds interactions between κ-car and LBG have a great influence in films’ properties e.g. moisture content, WVP. Therefore, different κ-car/LBG ratios can be used to tailor edible films with enhanced barrier and mechanical properties.     

Heat Curing of Soy Protein Films at Selected Temperatures and Pressures

Vacuum and temperature effects on moisture content, water vapor permeability (WVP), color (L, a, b, and ΔE), tensile strength (TS), elongation (E), and total soluble matter (TSM) of soy protein isolate (SPI) films were examined. SPI films were cured at 60, 72.5, or 85 °C and at 101.3, 81.32, or 61.32 kPa for 24 h. As a result of heat-curing moisture content, WVP, E, and TSM decreased, and total color difference and TS increased. Pressure, individually and interactively with temperature, significantly affected film moisture content, TS, and TSM.     

Preparation and characterization of proteinous film from lentil (Lens culinaris): Edible film from lentil (Lens culinaris)

This study was conducted to extract protein from lentil seed and prepare edible film from the protein and to determine mechanical, optical and barrier properties of lentil protein concentrate (LPC) film. The film was prepared from LPC (5 g/100 ml water) and glycerine (50%, w/w of LPC). Hunter color value (L, a and b), tensile strength, percentage elongation at break (E), puncture strength, water vapor permeability (WVP), moisture content after conditioning at 50% RH and 25 °C for 48 h and total soluble matter after immersion in water, were measured. In regarding to WVP, in spite of difference in film thickness and relative humidity of experiment in different studies, lentil protein film is comparable with other protein films. Characteristics of the lentil protein-based edible films were comparable with other edible protein films. LPC film had more red and less yellow color; it seems that the film had good mechanical properties and water vapor permeability in concomitant with good solubility.     

Comparing λ-carrageenan and an inulin blend as fat replacers in carboxymethyl cellulose dairy desserts. Rheological and sensory aspects

Carbohydrate-based fat replacers are of growing interest because, besides their physicochemical properties, they also have health-friendly characteristics. The study reported here aims to compare the effect of adding both λ-carrageenan and a blend (50:50) of short and long-chain inulin on the rheological behaviour and sensory properties of low-fat carboxymethyl cellulose (CMC) semi-solid dairy desserts. Low-fat samples with 0.03% λ-carrageenan or with 9% of the inulin blend displayed similar rheological behaviour to the full-fat control sample, i.e. there were no significant differences in either flow (σ₀, K, η₁₀ and n) or viscoelasticity (G′, G″, tan δ and η* at 1 Hz and η*_8Hz at 8 Hz). In general, samples with the same rheological behaviour but different fat content were perceived as having similar thickness, creaminess and smoothness. However, the substitution of fat by λ-carrageenan or inulin influenced both perceived sweetness and flavour.     

Rheological,mechanical and moisture sorption characteristics of cassava starch‐konjac glucomannan blend films

Cassava starch (ST)‐konjac glucomannan (KGM) blend films were prepared and their thermal, rheological, mechanical, moisture sorption properties and water vapour transmission rate were determined. Response surface methodology was employed for the preparation of films using different levels of ST, KGM and glycerol. All the filmogenic solutions exhibited shear thinning behaviour. Apparent viscosity and the dynamic rheological properties of filmogenic solutions varied considerably with KGM content. Rheological analysis revealed that the blend films are more appropriate than neat ST film for controlled drug release studies and for food coating. The melting temperature and enthalpy of fusion of the blend films were lower than that of neat ST film. When compared to neat starch film, the blend films showed broader peaks in DSC patterns, which suggests that incorporation of KGM decreased the crystallinity of ST. Mechanical properties, elongation at break and tensile strength of blend films were significantly higher (112.8% and 22.5 MPa, respectively) than those of neat ST film. Due to the more hydrophilic nature of KGM when compared to ST, the WVTR and moisture absorption of blend films were greater than that of neat ST film. Though KGM is more hydrophillic in nature, blend films with higher amount of KGM (0.643g) showed comparably lower values for both WVTR and moisture absorption than other blends. The solubility of the blend films was lower than that of neat starch film which also confirmed the strong intramolecular attraction between ST and KGM.     

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.     

Effects of glycerol,sorbitol, xylitol and fructose plasticisers on mechanical and moisture barrier properties of pullulan–alginate–carboxymethylcellulose blend films

The effects of glycerol, sorbitol, xylitol and fructose plasticisers on water sorption, mechanical properties, water vapour permeability (WVP) and microstructure of pullulan–alginate–carboxymethycellulose (PAC) blend films were investigated. At low plasticiser concentrations (below 7% w/w dry basis), antiplasticisation effect was observed, causing an increase in tensile strength (TS) but a decrease in the equilibrium moisture content. As glycerol concentration increased from 0% to 7%, TS increased from 68.1 to 69.6 MPa, whereas equilibrium moisture contents at 0.84 a_w decreased from 0.37 to 0.3 g H₂O g^?1 dry basis. At higher plasticiser concentrations (14–25% w/w), an opposite trend was observed on the PAC films, resulting in the reduction of TS and elevation of moisture content. Among the four plasticisers tested, the fructose‐plasticised films were the most brittle, showing the highest TS, but had the lowest elongation at break (EAB), WVP and equilibrium moisture content values than films plasticised with other polyols. On the other hand, glycerol resulted in the most flexible film structure, exhibiting opposite materials' properties as compared with the fructose‐plasticised films. For instance, at 25% (w/w) plasticiser concentration, EAB and WVP values of fructose‐plasticised films were 33.5% and 3.48 × 10^?6 g m Pa^?1 h^?1 m^?2, which were significantly lower than that of glycerol‐plasticised films (58.6% and 4.86 × 10^?6 g m Pa^?1 h^?1 m^?2, respectively). Scanning electron microscopy showed that the plasticised PCA films were less homogeneous and more porous than the unplasticised counterparts, indicating that plasticisers had an effect on the microstructural morphology of the film matrix.