Water vapour permeability of edible bilayer films of wheat gluten and lipids

Various formulations and methods of fabricating edible bilayer films consisting of wheat gluten as a structural layer and a thin lipid layer as a moisture barrier were investigated and examined for water vapour permeability. Solid lipids such as beeswax or paraffin wax deposited in a molten state onto the base film were the most effective water vapour barriers. A film consisting of wheat gluten, glycerol and diacetyl tartaric ester of monoglyceride as one layer, and beeswax as the other yielded a water vapour permeability of 0.0048 g mm m⁻² mmHg⁻¹ 24h⁻¹, which was less than that obtained with low density polyethylene.     

Effect of food ingredients and selected lipids on the physical properties of extruded edible films/casings

Films/casings produced using pectin (PN) and gelatin/sodium alginate blends (GSAB) containing 2.5 and 5% added corn oil (CO) or olive oil (OO) and non‐oil containing were manufactured using extrusion technology. Films/casings formed from PN and GSAB had great difference in properties of tensile strength, elongation, Young's modulus and puncture resistance. Quality and stability of films/casings were greatly enhanced on addition of oils. However, an oil addition of 2.5% was identified as optimal while 5% decreased the final films/casings quality. Oil addition increased (P < 0.05) films/casings thicknesses. Oil addition also decreased (P < 0.05) tensile strength, puncture resistance, Young's modulus and tear resistance of films/casings but increased their elongation properties, with the exception of converse effect of 2.5% CO on two films/casings. Olive oil and CO both reduced (P < 0.05) water vapour transfer rate (WVTR) of films/casings. However, no significant difference between films using different concentrations of oil was observed with respect to WVTR.     

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.     

Characterisation of composite edible films based on wheat starch and whey‐protein isolate

Composite films prepared by casting wheat starch and whey‐protein isolate at proportions of 100–0%, 75–25%, 50–50%, 25–75% and 0–100% were characterised. Combination of both substances gave continuous and homogeneous films. The more the starch is in a film, the more dull is the appearance. The highest water adsorption was observed for pure whey‐protein films and the lowest for pure wheat starch films with the final water content of 0.264 and 0.324 g water g d.m.^?1, respectively. An exponential equation well fitted the experimental data of water vapour kinetics (R² ≥ 0.99). The highest values of thickness and elongation at break were observed for films obtained by blending of wheat starch and whey protein. With the increasing content of whey‐protein isolate, the values of the swelling index and tensile strength increased from 34.31% to 71.01% and from 2.29 to 8.90 MPa, respectively. The values of water vapour permeability depended on humidity conditions and decreased slightly with the increasing content of whey‐protein isolate.     

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.     

Physical properties of edible coatings and films made with a polysaccharide from Anacardium occidentale L.

The effect of the concentrations of the polysaccharide from Anacardium occidentale L. (Policaju) and a surfactant (Tween 80) on relevant properties of edible coatings/films, in view of their application on apples (cv. Golden) was evaluated. The influence of the interactions between those two constituents on apples’ surface properties and on the coating/film’s wettability, water vapor permeability, opacity and mechanical properties was evaluated. The effects of the studied variables (polysaccharide and surfactant concentrations) were analyzed according to a 2² factorial design. Pareto bar charts were used to understand the most significant factors on the studied properties. The addition of surfactant reduced the cohesion forces, therefore reducing the surface tension and increasing the wettability; this resulted in an improved compatibility between the solution and the fruit skin surface. The opacity was also reduced. The results of each of the analyzed properties were adjusted to a polynomial, multifactor model, which provided a good fitting accuracy. This model is important once it will reduce the characterization work needed in subsequent applications of these coatings/films on foods.     

Permeability and Mechanical Properties of Cellulose-Based Edible Films

Factors affecting barrier properties [oxygen permeability (OP) and water vapor permeability (WVP)] and mechanical properties [tensile strength (TS) and elongation (E)] were investigated for methyl cellulose (MC) and hydroxypropyl cellulose (HPC) films. OP, WVP and TS of MC and HPC films increased as the molecular weight (MW) of the cellulose increased. E of MC films increased as MW increased, but E of HPC films was highest for the intermediate MW of 370,000. OP, WVP and TS of MC films were not a function of thickness, but E slowly increased as film thickness increased. OP and WVP of HPC films were not relatable to film thickness, but TS and E of HPC films slowly increased as film thickness increased. TS decreased and E increased for both film types as concentration of plasticizers was increased. Plasticizers enhanced or retarded OP and WVP of cellulose-based films, depending on their concentrations.     

Tensile and water barrier properties of cassava starch composite films reinforced by synthetic zeolite and beidellite

Composites films were prepared by the casting method using native cassava starch plasticized with glycerol and 3D or 2D synthetic fillers i.e. Beta zeolite and Na-beidellite type 2:1 phyllosilicate. Special attention was paid to the effect of the filler contents and type on the mechanical and barrier properties. It was shown that films reinforced with lyophilized Beta zeolite presented both high water solubility (WS) and water vapor permeability (WVP) values than the pristine starch whereas an improvement on the WVP was found for composites prepared from Na-beidellite or from non lyophilized Beta zeolite. For the two types of fillers, a drastic increase of the mechanical properties (especially in the Young’s modulus) was observed.     

小麦面筋蛋白的性质和转谷氨酰胺酶对其成膜性能的影响

以小麦面筋蛋白为研究对象,探讨小麦面筋蛋白的性质,转谷氨酰胺酶的作用和制备条件对膜性能的影响。结果表明,酶用量为20U/g,反应时间为120min,pH为11,甘油/谷朊粉1:2.5,塑料平板作为成膜介质和乙醇体积分数均为40%～50%时,膜的抗拉强度增加51%,阻水性提高23%,透光率提高了5.48倍。扫描电镜显示膜的超微结构更加细致光滑。说明蛋白质的性质对其成膜性能的影响至关重要,酶处理有助于改善膜的机械性能和透光性,选择合理的制备条件,可得到性能优良的小麦面筋蛋白膜。     

Dynamic mechanical properties and fractal analysis of texturized soybean protein/wheat gluten composite produced by high moisture extrusion

Texturized soybean protein (TSP) and wheat gluten were prepared at high moisture using a twin-screw extruder. Effects of feed moisture content, extrusion temperature and wheat gluten content on the dynamic mechanical properties, microstructures and fractal analysis of texturized soybean protein/wheat gluten composite were investigated. All extruded samples were well fitted with Burger's model in creep-recovery tests (R² ≥ 0.978). The creep-recovery rate decreased with an increasing extrusion temperature. The addition of wheat gluten increased the resistance to creep and the unrecoverable deformation of TSP samples. The extrusion parameters affected the microstructure and morphology of extruded products. The fractal dimension of TSP products decreased with an increase in moisture content and wheat gluten content. Texturized soybean protein (TSP) and wheat gluten composite could form well-structure products.     

Kefiran films plasticized with sugars and polyols: water vapor barrier and mechanical properties in relation to their microstructure analyzed by ATR/FT-IR spectroscopy

Kefiran, an exopolysaccharide produced by microorganisms present in kefir grains, is a glucogalactan that has several health promoting properties. In the present work the effect of different sugars (glucose, galactose, sucrose) and polyols (glycerol and sorbitol) as plasticizers on kefiran film properties was evaluated. Kefiran films were brittle and rigid and all the tested plasticizers improved film properties. They were all transparent with low opacity. Unplasticized kefiran films X-ray diffraction patterns were similar to those of plasticized ones, showing an amorphous-crystalline structure with low crystallinity degree. All films presented low a_w values (below 0.5) conferring protection properties against microorganism growth. The lowest permeability value was obtained with glucose as plasticizer whereas the best mechanical properties were obtained with glycerol addition.     

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.     

紫薯-低筋复配粉理化特性及其饼干制品品质分析

研究紫薯全粉不同添加量对低筋粉加工特性,及其饼干制品品质的影响。结果表明,紫薯全粉-低筋粉复配处理后,相较于低筋粉,10%～50%复配粉的持水性提高了0.90～2.08 g/g,持油性降低了0.05～0.18 g/g。随着紫薯全粉比例的增大,低筋粉的糊化起始温度(T_o)、峰值温度(T_p)、终止温度(T_c)逐渐升高,而热焓值(ΔH)逐渐减小,紫薯全粉的T_o、T_p、T_c则呈下降趋势,ΔH呈上升趋势。紫薯全粉的加入导致面团面筋膜撕裂,黏着性变差,当添加量达到50%时,复配粉基本不具备面筋网络形成能力,由其制成的饼干硬度和脆性相较于对照组分别降低2 276.49 g、5.43 mm,而抗性淀粉含量提高了8.42 g/100 g。10%～30%紫薯全粉添加量有利于饼干感官品质的提升,其可接受度程度依次为30%紫薯饼干>20%紫薯饼干>10%紫薯饼干。     

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.     

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

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

Effect of surfactants on water barrier and physical properties of tapioca starch/decolorized hsian-tsao leaf gum films

The objective of this research is to enhance the water barrier properties of tapioca starch/dHG edible films by incorporating sucrose ester surfactants with different HLB values. The moisture sorption isotherms, mechanical properties, microstructure and optical character of the resulting films were examined as well. It was found that the water barrier property of starch/dHG films is promoted significantly by surfactants, alongside a decreasing tendency in tensile strength and tensile strain at break. Scanning electron micrographs of the starch/dHG/surfactant composite films revealed the folded (multi-layer) microstructure in contrast to the homogeneous matrix of the control films. Starch/dHG/surfactant composite films show low opacity values. With increasing HLB value of the surfactant, the water vapor permeability and tensile strength of starch/dHG/surfactant composite films decrease. Moreover, the water vapor permeability, tensile strength, strain at break, and equilibrium moisture content of starch/dHG/surfactant composite films decrease when the surfactant content is increased, accompanied by an increasing tendency in opacity value. On the other hand, starch/dHG composite film with an emulsion of surfactant and beeswax shows a lower mechanical strength and significantly higher opacity value with less improvement in water vapor permeability.     

Edible films and coatings to prevent the detrimental effect of oxygen on food quality: Possibilities and limitations

Oxygen has a deleterious effect on the quality of a wide variety of food products. The application of edible films and coatings to food products represents a new approach to solve this problem. Edible films and coatings can include antioxidant agents in their formulation and at the same time, they represent a barrier to oxygen, which results in a better preservation of quality. The water activity of the product, as well as the ambient relative humidity, determines the antioxidant effect of films and coatings. This paper reviews the latest studies dealing with the effectiveness and application of antioxidant films and coatings.     

湿热-胶体改性对小麦面筋蛋白功能性质的影响

研究了在湿热条件下将羧甲基纤维素钠(CMC)、明胶、海藻酸钠、果胶、瓜尔胶这几种不同胶体作为添加剂添加到小麦面筋蛋白中,测定了其对小麦面筋蛋白功能性质的影响,主要以小麦面筋蛋白的粘稠性、乳化性和乳化稳定性、溶解性、起泡性这几个指标作为参考。实验结果表明,与简单混合相比,羧甲基纤维素钠、明胶、海藻酸钠、果胶在湿热条件下使小麦面筋蛋白的溶解性,乳化性和粘稠性都有一定幅度的提高,但是对小麦起泡性和乳化稳定性的影响不大;瓜尔胶在湿热条件下对小麦蛋白性质的影响与简单混合相比基本持平。     

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.