Physical Properties of Whey Protein–Hydroxypropylmethylcellulose Blend Edible Films

ABSTRACT: The formations of glycerol (Gly)‐plasticized whey protein isolate (WPI)–hydroxypropylmethylcellulose (HPMC) films, blended using different combinations and at different conditions, were investigated. The resulting WPI: Gly‐HPMC films were analyzed for mechanical properties, oxygen permeability (OP), and water solubility. Differences due to HPMC quantity and blend method were determined via SAS software. While WPI: Gly and HPMC films were transparent, blend films were translucent, indicating some degree of immiscibility and/or WPI–HPMC aggregated domains in the blend films. WPI: Gly‐HPMC films were stronger than WPI: Gly films and more flexible and stretchable than HPMC films, with films becoming stiffer, stronger, and less stretchable as the concentration of HPMC increased. However, WPI: Gly‐HPMC blended films maintained the same low OP of WPI: Gly films, significantly lower than the OP of HPMC films. Comparison of mechanical properties and OP of films made by heat‐denaturing WPI before and after blending with HPMC did not indicate any difference in degree of cross‐linking between the methods, while solubility data indicated otherwise. Overall, while adding HPMC to WPI: Gly films had a large effect on the flexibility, strength, stretchability, and water solubility of the film polymeric network, results indicated that HPMC had no effect on OP through the polymer network. WPI–HPMC blend films had a desirable combination of mechanical and oxygen barrier properties, reflecting the combination of hydrogen‐bonding, hydrophobic interactions, and disulfide bond cross‐linking in the blended polymer network.     

Effect of pH and addition of corn oil on the properties of whey protein isolate-based films using response surface methodology

Response surface methodology (RSM) was used to investigate pH and corn oil (CO) effects on the properties of films formed from whey protein isolate (WPI). Test films were evaluated for tensile strength (TS), puncture strength (PT), percentage elongation at break point (E), water vapour permeability (WVP) and oxygen permeability (OP). TS of WPI films increased with increasing pH, while addition of CO produced no trend. However, when WPI solution pH increased >10.0, film TS generally decreased with CO addition (>11%). E values increased dramatically with increasing levels of CO when pH for WPI solutions were >8.5. However, pH had no effect on E values. WPI solutions possessing high pH values (maximum pH value of 10.62) produced WPI films with the highest PT values. WVP had a quadratic relationship with pH and CO addition. OP had an inversely linear relationship with increasing pH (6.5–10.5) and a quadratic relationship with CO addition. Optimal pH (9.88) and CO level (2.93%), determined from physical test film data, were predicted by RSM.     

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.     

Whey protein isolate-based edible films as affected by protein concentration,glycerol ratio and pullulan addition in film formation

Edible films were prepared from whey protein isolate (WPI), and characterized in order to select a best combination of protein concentration and glycerol (Gly) ratio. 5%, 7% and 9% (w/v) WPI were used at three WPI:Gly ratios (3.6:1; 3:1; and 2:1). 5% WPI with a 3.6:1 WPI:Gly ratio showed the best combination with factors considered being thickness and water vapor permeability (WVP), while the 9% WPI with 3.6:1 WPI:Gly showed the best result as seen from the oxygen permeability (OP). Further studies were conducted by adding pullulan (PUL) at different WPI:PUL ratios (1:0; 1:1; 2:1; 3:1; 4:1; 5:1; 6:1; 8:1; 10:1) to a selected film in order to investigate the effect of pullulan on thickness, OP, WVP, moisture content (MC), film solubility (FS) and morphology using scanning electron microscopy (SEM). WPI–PUL film had a good appearance and 1:1 WPI:PUL resulted in films with greatest values of OP, WVP, MC, FS, and transmittance. The SEM micrographs showed many pinholes and a favorable structure for the low barrier ability. However, addition of PUL at low concentration was good enough to significantly modify these properties, hence improving the potential characteristics of WPI-based films for food applications.     

Whey protein-polysaccharide blended edible film formation and barrier, tensile, thermal and transparency properties

BACKGROUND: Films made from different protein (P) or polysaccharide (PS) materials have widely different properties. The objective of this study was to determine whether whey protein isolate (WPI)‐PS blended films possess a combination of properties intermediate and possibly superior to WPI or PS film alone. RESULTS: Oxygen permeability (OP) and tensile strength (TS) for PS‐WPI blended films were intermediate between the OP and TS properties of pure methycellulose (MC), hydroxypropylmethylcellulose (HPMC) or sodium alginate (SA) film and pure WPI film. Starch‐WPI blends gave the weakest films. Water vapor permeability values for all pure and blended films were similar. Blended films made of MC, HPMC or SA with WPI had lower transparency than pure MC, HPMC, SA or WPI films. Differential scanning calorimetry thermograms obtained from the blended films exhibited a single glass transition temperature (T_g) at an intermediate value between the T_g values of the pure films. CONCLUSIONS: Whether properties of PS‐WPI blended films are intermediate to properties of the pure PS and WPI film depends on the particular PS and specific property. In the case of MC or HPMC with WPI, the blended films reflect the higher TS of the PS and lower OP of the WPI. Copyright © 2011 Society of Chemical Industry     

Starch–methylcellulose–whey protein film properties

Four % (wt/wt) aqueous solutions were prepared at corn starch:methylcellulose:whey protein isolate (CS:MC:WPI) ratios of 2:2:2, 1:2:3, 2:1:3, 2:2:0, 1:2:0 and 2:1:0. Glycerol (gly) was used as a plasticiser at CS–MC–WPI:gly ratios of 2:1, 2.5:1 and 3:1. CS–MC–WPI blend films were stronger than CS–WPI films and had lower oxygen permeability (OP) than MC–WPI films. The highest tensile strength (TS) of blend films was 8.01 ± 3.41 MPa, at CS:MC:WPI ratio of 2:2:0 and CS–MC–WPI:gly ratio of 3:1. Lowest OP value was 45.05 ± 7.24 cm³ μm m^?2 per day kPa^?1, at CS:MC:WPI ratio of 2:2:2 and CS–MC–WPI:gly ratio of 3:1. OP values were predictable based on relative amounts of components. However, TS and elastic modulus properties of the CS–MC–WPI blend films did not reflect the relative amounts of the components. All of CS–MC–WPI films were translucent indicating some degree of immiscibility among the CS, MC and WPI. These results indicate the influence of complex molecular interactions among the components.     

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.     

Antimicrobial Effects of Lactoferrin, Lysozyme, and the Lactoperoxidase System and Edible Whey Protein Films Incorporating the Lactoperoxidase System Against Salmonella enterica and Escherichia coli O157:H7

Lactoferrin (LF), lysozyme (LZ), the lactoperoxidase system (LPOS), and edible whey protein isolate (WPI) films incorporating LPOS were studied for inhibition of Salmonella enterica and Escherichia coli O157:H7. Antimicrobial effects of LF (5 to 40 mg/mL), LZ (1 to 20 mg/mL), and LPOS (0.5% to 5.0% [w/v] [0.03–.25 g/g, dry basis]) were examined by measuring turbidity of antimicrobial‐containing media after inoculation and by examining cell inhibition by WPI films incorporating LPOS (LPOS‐WPI films) on an agar recovery medium. Elastic modulus (EM), tensile strength (TS), percent elongation (%E), oxygen permeability (OP), and Hunter L, a and b of WPI films incorporating 0.03 to 0.25 g/g of LPOS were compared with those of plain WPI films without LPOS. The growth of S. enterica and E. coli O157:H7 (4 log colony‐forming units [CFU]/mL) in tryptic soy broth (TSB) was not prevented by LF at ≥20 and ≥40 mg/mL, respectively. S. enterica and E. coli O157:H7 in TSB were not inhibited by LZ at ≥ 6 and ≥ 20 mg/mL, respectively. LPOS at concentrations of 2.75% (w/v) and 1.0% (w/v) reduced S. enterica and E. coli O157:H7 to below the limit of detection (1 CFU/mL) in TSB, respectively. LPOS‐WPI films (0.15 g/g) completely inhibited S. enterica and E. coli O157:H7 (4 log CFU/cm²), inoculated either onto agar before placing the film disc or onto top of the film disc. Incorporation of 0.25 g/g of LPOS decreased EM, TS, and %E. The oxygen barrier property of WPI films was improved with the incorporation of LPOS at 0.15 to 0.25 g/g.     

Mechanical and Barrier Properties of Edible Chitosan Films as affected by Composition and Storage

Oxygen permeability coefficients (OP), water vapor permeability coefficients (WVP), ethylene permeability coefficients (EP), tensile strength (TS) and percent elongation (%E) at break values were determined for chitosan films plasticized with glycerin at two concentrations (0.25 and 0.50 mL/g chitosan). Film samples were tested after 0, 2, 4, 8 and 12 wk of storage. After an initial drop in permeability during the first 2 wk of storage, mean OP (4.6 × 10^?5 cc/m-day-atm) and mean EP (2.3 × 10^?4 cc./m.day.atm) remained constant while mean WVP (2.2 × 10^?1 g/m-day-atm) decreased with respect to storage time. TS values (15–30 MPa) decreased and %E values (25%–45%) increased with respect to storage time. The stability of OP and EP values with storage was not expected, while the change in mechanical properties was as expected.     

Edible Films and Coatings from Soy Protein

A method was developed by which films could be prepared from commercial isolated soy protein (ISP). ISP was treated with alkali (ATISP) to alter film orooerties. Water vapor oermeability (WVP). oxygen‘permeability (O₂P), tensile strength (TS), percent elongatidn (%E), and appearance of ISP and ATISP were compared. Alkali treatment had no effect on WVP. O₂P, and TS, gave hieher %E, and improved film appearance. Films properties were also compared at pH 6, 8, 10, and 12. In general, pH 6 gave higher WVP and O₂P and lower TS and %E; while higher pH gave lower WVP and O₂P and higher TS and %E. ATISP films could not be produced at pH 6. Film appearance generally improved with increased pH.     

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.     

Water Solubility, Mechanical, Barrier, and Thermal Properties of Cross-linked Whey Protein Isolate-based Films

Water solubility, hermal properties, tensile strength, percent elongation, oxygen permeability (OP), water‐vapor permeability (WVP) of cross‐linked glycerol plasticized whey protein isolate films were studied to determine the effect of cross‐linkers (glutaraldehyde, formaldehyde, dialdehyde starch, carbonyldiimidazole, and UV irradiation) on film properties. With the exception of UV treatment, solubility of the films decreased (P>0.05) upon treatment of the film‐forming solutions with chemical cross‐linkers. Tensile strength increased (P>0.05), whereas percent elongation was not affected by cross‐linking. Chemical cross‐linking increased (P>0.05) WVP and decreased (P>0.05) OP of the films. UV treatment had no effect on WVP and O P. With the exception of UV‐treated films, both onset temperature and degradation temperatures, as determined by differential scanning calorimetry, were increased upon cross‐linking.     

Barrier and tensile properties of whey protein–candelilla wax film/sheet

Barrier and tensile properties were compared for whey protein isolate- (WPI-) based solution-cast films, extruded sheets and extruded sheets subsequently thinned into films by compression. Solution-cast films were made from mixtures of WPI and glycerol (GLY) in water. Sheets were made by feeding WPI, GLY, and water to a twin-screw co-rotating extruder. In each case, candelilla wax (CAN) was added at 0, 5 or 7.5 g CAN/100 g dry mix to determine the effect on the barrier and tensile properties. Compressed extruded films were made by thinning extruded sheets using a Carver Press equipped with heated platens. Water vapor permeability (WVP), oxygen permeability (OP) and tensile properties were measured. Scanning electron microscopy (SEM) images were also taken.     

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     

Oxygen permeability and mechanical properties of banana films

Banana flour, obtained from banana cv. Kluai Namwa, was used to form banana films. The effect of banana flour, glycerol (Gly) and pectin content on film oxygen permeability (OP) and mechanical properties of banana films were studied. Banana flour content significantly affected film OP; whereas, Gly and pectin contents did not significantly affect film OP. Increasing banana flour and pectin contents enhanced film strength; thus, it showed higher film elastic modulus (EM) and tensile strength (TS) but less film % elongation (% E) (p ⩽ 0.05). In contrast, increasing Gly content reduced the film strength and improved film flexibility; therefore, it decreased film EM and TS but increased film % E (p ⩽ 0.05). Banana films showed good sealability, which can make these films suitable as sachets or pouches for dry foods, thus reducing the need for plastic materials.     

Improved water vapor barrier of whey protein films by addition of an acetylated monoglyceride

This study aimed to determine to what extent the water-vapor barrier of whey protein isolate (WPI) films could be improved by adding a lipid and make laminate and emulsion films. The laminate whey protein–lipid film decreased the water vapor permeability (WVP) 70 times compared with the WPI film. The WVP of the emulsion films was half the value of the WPI film and was not affected by changes in lipid concentration, whereas an increased homogenization led to a slight reduction in WVP. The mechanical properties showed that the lipid functioned as an apparent plasticizer by enhancing the fracture properties of the emulsion films. This effect increased with homogenization. The maximum strain at break was 117% compared with 50% for the less-homogenized emulsion films and 20% for the pure WPI films. Phase-separated emulsion films were produced with a concentration gradient of fat through the films, but pure bilayer films were not formed.     

热处理和碱处理对可食性大豆分离蛋白膜性能的影响

研究了热处理和碱处理对可食性大豆分离蛋白(SPI)膜性能的影响。对成膜液进行适当的加热和调节pH可以提高SPI膜的抗拉强度(TS)和伸长率(E),降低水蒸气透过系数(WVP)。调节成膜液的pH到9,在70℃加热20min,所得到的膜机械性能和阻湿性能最好。     

Listeria monocytogenes Inhibition by Whey Protein Films and Coatings Incorporating the Lactoperoxidase System

Antimicrobial effects of whey protein isolate (WPI) films and coatings incorporating the lactoperoxidase system (LPOS) against Listeria monocytogenes were studied by turbidity, plate counting, disc‐covering, and disc‐surface‐spreading tests using various growth media. Survival of L. monocytogenes applied to smoked salmon before or after the coating was monitored immediately after application and during storage at 4 °C and 10 °C for up to 35 d. Tensile properties (elastic modulus [EM], tensile strength [TS], elongation [E]), oxygen permeability (OP), and color (Hunter L, a, b) of WPI films, with and without LPOS, were also compared. LPOS inhibited L. monocytogenes in broth and on agar media. WPI films incorporating 29 mg of LPOS per gram of film (dry basis) inhibited 4.2 log colony‐forming units (CFU)/cm² of L. monocytogenes inoculated on agar media. WPI coatings prepared with LPOS at 0.7% (w/w) in a coating solution (40 mg LPOS/g coating [dry basis]) initially reduced >3 and 1 log CFU/g of L. monocytogenes and total aerobic microorganisms in smoked salmon, respectively. The WPI coatings incorporating LPOS prevented the growth of L. monocytogenes in smoked salmon at 4 °C and 10 °C for 35 d and 14 d, respectively. The tensile properties, oxygen permeability, and color of WPI films were not significantly changed by incorporation of LPOS (P >0.05).     

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.     

Liquid and vapour water transfer through whey protein/lipid emulsion films

BACKGROUND: Edible films and coatings based on protein/lipid combinations are among the new products being developed in order to reduce the use of plastic packaging polymers for food applications. This study was conducted to determine the effect of rapeseed oil on selected physicochemical properties of cast whey protein films. RESULTS: Films were cast from heated (80 °C for 30 min) aqueous solutions of whey protein isolate (WPI, 100 g kg^?1 of water) containing glycerol (50 g kg^?1 of WPI) as a plasticiser and different levels of added rapeseed oil (0, 1, 2, 3 and 4% w/w of WPI). Measurements of film microstructure, laser light‐scattering granulometry, differential scanning calorimetry, wetting properties and water vapour permeability (WVP) were made. The emulsion structure in the film suspension changed significantly during drying, with oil creaming and coalescence occurring. Increasing oil concentration led to a 2.5‐fold increase in surface hydrophobicity and decreases in WVP and denaturation temperature (T_max). CONCLUSION: Film structure and surface properties explain the moisture absorption and film swelling as a function of moisture level and time and consequently the WVP behaviour. Small amounts of rapeseed oil favourably affect the WVP of WPI films, particularly at higher humidities. Copyright © 2010 Society of Chemical Industry