Plasticized Whey Protein Edible Films: Water Vapor Permeability Properties

Heat treatment, protein concentration, and pH effects on water vapor permeability (WVP) of plasticized whey protein films were examined. The best film formation conditions were neutral pH, aqueous 10% (w/w) protein solutions heated for 30 min at 90°. Isoelectric point adjustment of whey protein with calcium ascorbate buffer increased WVP with increasing buffer concentration, The importance of vacuum application to minimize film pore size was identified using scanning electron microscopy. Polyethylene glycol, glycerol and sorbitol plasticizer concentration affected film WVP. Determining the effects of relative humidity on WVP for plasticized whey protein films enabled prediction of film behavior under any water vapor partial pressure gradient.     

Plasticizing Effects of Beeswax and Carnauba Wax on Tensile and Water Vapor Permeability Properties of Whey Protein Films

ABSTRACT: The possible plasticizing effect of beeswax (viscoelastic wax) and carnauba wax (elastic wax) on tensile and water vapor permeability properties of whey protein isolate (WPI) films was studied. For the experiments, 3 groups of films with different WPI:glycerol ratios (1:1; 1.5:1; 2:1, 2.5:1, and 3:1) were prepared. The 1st group was made without the addition of wax, and the latter 2 groups were made with the addition of beeswax and carnauba wax, respectively, mixing 1 part of wax to 1 part of WPI. Lipid particle size, water vapor permeability, tensile properties, and thickness of films were analyzed and measured. The results show that the incorporation of beeswax produced a plasticizing effect in WPI:glycerol films, whereas carnauba wax produced an anti-plasticizing effect. The moisture barrier properties of WPI:glycerol films benefit from the addition of beeswax, by both increase of the hydrophobic character and decrease of the amount of hydrophilic plasticizer required in the film.     

Water Vapor Permeability and Solubility of Films from Hydrolyzed Whey Protein

ABSTRACT: The effects of whey protein hydrolysis on film water vapor permeability (WVP) and solubility at 3 plasticizer levels were studied. Little or no significant difference (p > 0.05) appeared for film WVP between unhydrolyzed whey protein isolate (WPI), 5.5% degree of hydrolysis (DH) WPI and 10% DH WPI films at comparable plasticizer contents. However, increase in glycerol (gly) content significantly increased film WVP. Thus, reduction in WPI molecular weight (MW) through hydrolysis may be a better approach to improving film flexibility than addition of plasticizer. Both 5.5% and 10% DH WPI had significantly different (p ≤ 0.05) film solubility compared to unhydrolyzed WPI. Soluble Protein (SP) and total soluble matter (TSM) of hydrolyzed WPI films were much higher than for unhydrolyzed WPI films.     

Water Vapor Permeability, Solubility, and Tensile Properties of Heat-denatured versus Native Whey Protein Films

Whereas native whey protein films were totally water soluble, heat denatured films were insoluble. Heat-denatured whey protein films had higher tensile properties than native whey protein films. However, native and heat-denatured films had similar water vapor permeability (WVP). The pH of the film-forming solution did not have any notable effect on film solubility, mechanical properties, or WVP. Results suggest that covalent cross-linking due to heat denaturation of the whey protein is accountable for film water insolubility and higher tensile properties but does not affect WVP of the films.     

Permeability of d-Limonene in Whey Protein Films

The effects of temperature, relative humidity (%RH) and permeant concentration on aroma permeability were investigated in edible whey protein isolate (WPI) films. An orthogonal regression was performed to ascertain significance of these factors. Temperature and %RH had exponential effects on d-limonene permeability, interacting synergistically to influence aroma transport in WPI polymer films. Permeability of d-limonene in WPI polymer films was not influenced by permeant concentration in the range 62 to 226 ppm (mol/mol). The predictive equation generated by regression analysis could be potentially useful for edible packaging design within the given temperature, %RH, and concentration ranges. The Arrhenius-type format also provided insight into the temperature-sensitivity of WPI films and confirmation of the influence of %RH on permeability activation energy.     

Whey Protein Emulsion Film Performance as Affected by Lipid Type and Amount

Beeswax, candelilla wax, carnauba wax, and a high-melting fraction of anhydrous milkfat were homogenized with whey protein to produce edible emulsion films. Lipid type and amount were important in controlling the emulsion film water vapor permeability (WVP). The WVPs of the beeswax and milkfat emulsion films were significantly lower than that of films from lower moisture transmitters, carnauba and candelilla wax. Lipid WVP and degree of viscoelasticity determined the barrier properties of the films. A significant reduction in WVP of whey protein films could be achieved using large volume fractions of lipid depending on lipid type.     

Water Vapor Permeability of Mammalian and Fish Gelatin Films

ABSTRACT:  Water vapor permeability of cold- and warm-water fish skin gelatins films was evaluated and compared with different types of mammalian gelatins. Alaskan pollock and salmon gelatins were extracted from frozen skins, others were obtained from commercial sources. Water vapor permeability of gelatin films was determined considering differences on percent relative humidity (%RH) at the film underside. Molecular weight distribution, amino acid composition, gel strength, viscoelastic properties, pH, and clarity were also determined for each gelatin. Water vapor permeability of cold-water fish gelatin films (0.93 gmm/m²hkPa) was significantly lower than warm-water fish and mammalian gelatin films (1.31 and 1.88 gmm/m²hkPa, respectively) at 25 °C, 0/80 %RH through 0.05-mm thickness films. This was related to increased hydrophobicity due to reduced amounts of proline and hydroxyproline in cold-water fish gelatins. As expected, gel strength and gel setting temperatures were lower for cold-water fish gelatin than either warm-water fish gelatins or mammalian gelatins. This study demonstrated significant differences in physical, chemical, and rheological properties between mammalian and fish gelatins. Lower water vapor permeability of fish gelatin films can be useful particularly for applications related to reducing water loss from encapsulated drugs and refrigerated or frozen food systems.     

Role of Covalent and Noncovalent Interactions in the Formation of Films from Unheated Whey Protein Solutions Following pH Adjustment

ABSTRACT: Films were formed from heated whey protein isolate (WPI) solutions (heated [H] films) and from unheated WPI solutions following adjustment to pH 11, with subsequent readjustment to pH 7 (unheated, readjusted [UR] films) or without readjustment to pH 7 (unheated, unadjusted films [UU] films). UU and UR films had significantly lower % elongation, tensile strength, and Young's modulus than H films. Film solubility and dispersion in water were in the order: H films < UU films < UR films. Free sulphydryl groups were lower and disulphide-mediated polymerization was higher in heated than in unheated WPI solutions whereas solubility of H films increased in the presence of dithiothreitol.     

Hydrophilic Edible Films: Modified Procedure for Water Vapor Permeability and Explanation of Thickness Effects

The ASTM E96 Standard Method for determining water vapor permeability (WVP) was modified for hydrophilic edible films. Accurate measurement of relative humidity conditions and maintenance of 152 m/min air speeds were essential outside the test cups. The WVP Correction Method was developed to account for the water vapor partial pressure gradient in stagnant air layer of the test cup. Errors were as high as 35% without this correction. Applying these guidelines explained commonly observed thickness effects on WVP values of hydrophilic films. Relative humidity was the cause of observed thickness effects.     

Water Vapor Permeability of Caseinate-Based Edible Films as Affected by pH, Calcium Crosslinking and Lipid Content

Edible films were cast from solutions of sodium or calcium caseinate and from emulsions of these proteins with acetylated monoglyceride, beeswax, and stearic acid. The water vapor permeabilities of the films were evaluated at 25°C using the ASTM E96–80 method, modified to calculate the % relative humidity at the film underside. Adjustment to pH 4.6 (isoelectric point), calcium ion crosslinking and combined effects of calcium ascorbate buffer (pH 4.6) reduced water vapor permeability of sodium caseinate films by 36%, 42%, and 43%, respectively. Calcium caseinate-beeswax emulsion films had water vapor permeabilities up to 90% lower than pure sodium caseinate films. Water vapor permeability varied by a factor of two depending on emulsion film orientation, indicating nonisotropic structure.     

Tensile and Barrier Properties of Edible Films Made from Whey Proteins

ABSTRACT: Whey protein isolate (WPI)-based edible biopolymer films were prepared using a film-forming stage designed to provide heat-induced gelation. Effects of whey-protein ratios, calcium, glycerol (plasticizer), and emulsion droplet incorporation on film tensile and barrier properties were investigated. Protein ratios had less influence on tensile strength, elongation, and water vapor permeability than glycerol and calcium ion concentrations. Semitransparent films with reasonably high tensile and UV-light barrier properties and moderate water vapor barrier properties were prepared from WPI:20% glycerol:10 mM calcium solutions. Microstructure analysis revealed the influence of glycerol and calcium concentrations on gel networks, which could be related to film tensile properties.     

Water Vapor Permeability and Mechanical Properties of Soy Protein Isolate Edible Films Composed of Different Plasticizer Combinations

Water barrier and mechanical properties were measured for soy protein isolate (SPI) films plasticized with glycerol (GLY) and 1 of the plasticizers (propylene glycol [PG], polyethylene glycol [PEG], sorbitol [SOR], or sucrose [SUC]) at a ratio of 25:75, 50:50, 75:25, and 0:100. Plasticizer type as well as the plasticizer ratio in the GLY: plasticizer mixtures affected the film water barrier and mechanical properties. An addition of as little as 25% of a less hygroscopic plasticizer in the mixture induced significant reduction in water vapor permeability (WVP) of SPI films. However, at least 50% of the mixture needs to be GLY to show significant improvement in tensile strength (TS). From our experimental design, 50:50 GLY:SOR was the recommended combination because of its comparatively low WVP value and relatively high flexibility and strength. Incompatibility of GLY:PEG plasticizer mixture in SPI film was observed by surface migration of PEG from the film matrix.     

Heat Curing of Whey Protein Films

Heat curing of edible whey protein isolate (WPI) films was studied as a means of improving mechanical and water vapor barrier properties. Curing temperature and relative humidity (RH) effects on the rate of change of maximum tensile stress (TS), elongation at break (E), Young's Modulus (Y_m), and water vapor permeability (WVP) were investigated. Cure time linearly affected TS and Y_m, while influencing E and WVP exponentially. Increased cure temperature and reduced RH accelerated TS increase, E and Y_m decrease, and increased improvement in WVP barrier properties. These data support the hypothesis that heat curing may elicit additional cross-linking of protein, yielding increased TS and decreased E and WVP; however, further work is required to confirm this hypothesis.     

Formation Conditions, Water-vapor Permeability, and Solubility of Compression-molded Whey Protein Films

ABSTRACT: Films based on whey protein isolate (WPI) were formed using compression molding. Compression molded films could be formed using 30% to 50% moisture content or glycerol content WPI at 104 °C to 160 °C for 2 min. Films made from water-WPI mixtures were brittle and insoluble and had water-vapor permeability values independent of starting water-WPI mixture moisture content, molding temperature, or molding pressure. Gly-WPI films produced at 104 °C were flexible and partially soluble. Gly-WPI films produced at 140 °C were also flexible but nearly insoluble. Glycerol content and molding temperature and pressure had little effect on water-vapor permeability values of Gly-WPI films over the range of conditions studied.     

Polarity Homogeneity and Structure Affect Water Vapor Permeability of Model Edible Films

A continuous gravimetric measurement method was perfected to determine with accuracy the water vapor permeability of edible films. Two substances, methylcellulose and paraffin wax, with different physicochemical properties, were used as films. Factors affecting permeability included the polarity of film components, the homogeneity or dispersion of material in the film and the structure which depends on the distribution of paraffin wax in the composite films. The thickness and the Water Vapor Transmission Rate (WVTR) measurement methods resulted in different values for permeability. WVTR increased with hydrophilicity and heterogeneity. Modeling trials con-cerning water vapor transport indicated the major influence that structure had on permeability. Waxlaminated fiIms had a very high barrier efficiency, comparable with that of synthetic films.     

Sensory Attributes of Whey Protein Isolate and Candelilla Wax Emulsion Edible Films

ABSTRACT: Whey protein isolate (5% w/v) films were plasticized with sorbitol or glycerol, and candelilla wax (0.8% w/ v) was added to produce whey protein isolate and candelilla wax emulsion edible films. The films were cut into 7.62 cm × 2.54 cm strips and evaluated by a 15-member trained sensory panel for milk odor, transparency/opaqueness, sweetness, and adhesiveness using a structured 9-point intensity scale. The films had no distinctive milk odor; however, they were perceived to be slightly sweet and adhesive by the trained sensory panel. Whey protein isolate films without candelilla wax were clear and transparent, whereas candelilla wax containing films were opaque.     

Tensile and moisture barrier properties of whey protein–beeswax layered composite films

BACKGROUND: There is a lack of research on producing layered protein–lipid composite films with improved tensile and barrier properties compared to films from individual components. Several film‐forming parameters were hypothesized to influence the extent to which lipids were either dispersed within or layered upon whey protein films. Film‐forming parameters investigated were ratio of whey protein isolate (WPI) to beeswax (BW), homogenization method, sodium chloride (NaCl) concentration, and BW particle size. RESULTS: Film percent elongation (E) increased, while tensile strength (TS) and elastic modulus (EM) decreased when BW was incorporated into WPI films, demonstrating a lubricant effect of the BW. Mean water vapor permeability values for WPI film decreased by 57% when the film composition was modified by the addition of 40% BW. BW phase separation was observed in all of the tested films. Particle size of BW in the film‐forming emulsions was larger in the presence of NaCl (100 mmol L^?1), indicating a neutralization of particle charge. However, the addition of NaCl did not improve the moisture barrier of WPI‐BW film over the range of film‐forming conditions used in the study. CONCLUSION: The results from this study are useful in determining formulations and conditions for the production of composite films from WPI and BW with improved tensile and moisture barrier properties. Copyright © 2008 Society of Chemical Industry     

Structural and Functional Properties of Caseinate and Whey Protein Isolate as Affected by Temperature and pH

The structural properties, i.e., active sulfhydryl (SH), flexibility and hydrophobicity, and functional properties, i.e., solubility, emulsion activity (EA), emulsion stability (ES), foam overrun (FO) and foam stability (FS), of commercial sodium caseinate (SC) and whey protein isolate (WPI) solutions were investigated at pH 6, 7 and 8 and at 25, 55 and 65°C. WPI contained a higher concentration of active SH and was more hydrophobic than SC. WPI provided comparable solubility and EA, lower FO, but higher FS than SC. Temperature and pH effects on the two proteins were somewhat inconsistent.     

氧化咖啡酸交联乳清蛋白膜的热学、光学特性及水汽渗透率、消化率研究

采用氧化咖啡酸作为交联剂,研究其对乳清蛋白交联所成膜的热、光、水汽渗透和消化等功能特性。咖啡酸溶液经氧化后以质量分数2%和4%的量(以蛋白量为基础)加入到6g/100mL、90℃热变性的乳清蛋白溶液(pH8.0),采用铺展法制备蛋白膜。利用SDS-PAGE、差示扫描量热法、热重技术等方法来表征氧化咖啡酸对乳清蛋白的交联性和膜功能性的影响。结果表明:氧化咖啡酸主要通过促进二硫键和部分非还原共价键交联蛋白,使蛋白成膜的热稳定性提高。此外,这种交联处理能显著降低膜材料的光通透率和透明性,但对水汽渗透率无显著性降低作用。体外消化实验结果显示较高质量分数的氧化咖啡酸处理可显著降低膜的消化性。     

可食性膜阻水特性的研究

本实验采用拟杯子法,以CaCl2为吸水材料,以棉布为膜载体,在温度25±2 ℃、相对湿度为90%±2%的条件下,测定了各种膜的水蒸气透过率,并比较了它们的阻水特性.结果表明,海藻酸钠膜是具有最佳阻水性的多糖膜;明胶膜比大豆蛋白膜阻水性更优;脂质膜的阻水率按以下顺序依次增大:月桂酸＜棕榈酸＜硬脂酸＜石蜡＜蜂蜡,乙酰化单甘酯的阻水性优于单甘酯;增塑剂山梨醇、甘油及乙二醇的加入会使膜的阻水性降低;在三元膜中,脂质膜用作被膜剂比用作乳化剂具有更好的效果.