Optical and surface properties of whey protein isolate coatings on plastic films as influenced by substrate,protein concentration,and plasticizer type

Composite film structures of common plastic polymers including polypropylene (PP) or poly(vinyl chloride) (PVC) with whey protein isolate (WPI) coatings may be obtained by a casting method. Optical and surface properties of the resulting WPI‐coated plastic films, as affected by protein concentration and plasticizer type, were investigated to examine the biopolymer coating effects on surface modification with polymeric substrates of opposite polarity. The measured properties involved specular gloss, color, contact angle, and critical surface energy. Regardless of the substrates, WPI‐coated films possessed excellent gloss and no color, as well as good adhesion between the coating and the substrate when an appropriate plasticizer was added to the coating formulations. The protein concentration did not significantly affect gloss of WPI‐coated plastic films. Among five plasticizers applied, sucrose conferred the most highly reflective and homogeneous surfaces to the coated films. The WPI coatings were very transparent and the coated films with various protein concentrations and plasticizers showed no noticeable changes in color. Experimental results suggest that WPI coatings formulated with a proper plasticizer can improve the visual characteristics of the polymeric substrate and enhance water wettability of the coated plastic films. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 335–343, 2004     

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.     

Dependence of Coating Thickness on Viscosity of Coating Solution Applied to Fruits and Vegetables by Dipping Method

ABSTRACT: Hydroxypropyl methylcellulose solutions were used as coating systems in this study and solution concentrations, viscosity, densities, and surface tensions were characterized. Fuji apples were coated by dipping and stored 4 d at room temperature, after which the internal oxygen and carbon dioxide were measured. Results indicated that coating thickness varied with viscosity, concentration, density, and draining time of the biopolymer solution. Coating thickness relates to the square root of viscosity and the inverse square root of draining time, which agrees with the theoretical approach for flat plate dip-coating inlow-capillary-number Newtonian liquids. These results indicate the possibility of controlling coating thickness and internal gas composition based on coating solution properties. Keywords: coating thickness, viscosity, fruits, vegetables, modified atmosphere     

Internal Modified Atmospheres of Coated Fresh Fruits and Vegetables: Understanding Relative Humidity Effects

ABSTRACT: Internal atmosphere modification in fruits and vegetables by surface film coatings depends on film permeability, coating thickness, and fruit surface coverage. Research in this area has been mostly empirical, with unpredictable results and diverse conclusions. To reduce variability, it is necessary to have a better understanding of factors that may influence the response of coatings applied to fruits. One factor is relative humidity (RH), which is known to affect the permeability of biopolymer films. By using steady-state mathematical models as tools, we hypothesize that fruits coated with hydrophilic films will be largely influenced by the RH of storage conditions. For hydrophobic materials, RH would have less influence on coating performance.     

Whey Protein Coatings for Fresh Fruits and Relative Humidity Effects

ABSTRACT: Whey protein isolate (WPI) films have proven to be excellent gas barriers in previous studies, making them potential coatings for fresh produce. WPI‐coated apples and controls were stored at 20 °;C under RH's ranging from 54 to 92%. Results showed performance of WPI coatings depended on the environment RH. The internal oxygen was lowered, and carbon dioxide increased with decreasing RH conditions. RH did not affect control fruits. At low RH (about 70 to 80% RH), anaerobic respiration was induced in coated fruits due to low oxygen levels (about 0.025 atm). Controlling thickness and film permeability will allow attainment of the appropriate oxygen and carbon dioxide levels for coated fruit.     

Oxygen Barrier Properties of Whey Protein Isolate Coatings on Polypropylene Films

Oxygen permeation characteristics of whey protein isolate (WPI) coatings on polypropylene (PP) films were investigated to examine the feasibility of WPI coating as a novel biopolymer oxygen barrier for food packaging applications. Heat‐denatured aqueous solutions of WPI with several plasticizers including glycerol, sorbitol, sucrose, propylene glycol, and polyethylene glycol were applied on the surfaces of PP films previously treated with corona discharge. Among plasticizers used, sucrose conferred the best oxygen barrier property to the WPI‐coated films. Oxygen permeability (OP) of the resulting WPI‐coated films increased significantly with temperature, showing very good agreement with the Arrhenius model. OP of the coated films also increased exponentially with relative humidity.     

Crystal morphology of mixtures of tripalmitin and butterfat

Blends of butterfat and tripalmitin are of interest for use as moisture barriers in edible films. Tripalmitin was blended with butterfat in the ratios 100:0, 90:10, 80:20, and so on through to 10:90 and 0:100. Crystal morphologies of squash and smear preparations were determined by polarizing light microscopy. Samples were stored at 19–22°C and re-examined after 6 d and after 30 d. Morphology was strongly dependent on composition and the presence of a coverslip. Morphology was less dependent on polymorphic form and age. Barrier properties depend more strongly on morphology than on polymorphic form.     

Properties of novel hydroxypropyl methylcellulose films containing chitosan nanoparticles

In this study, chitosan nanoparticles were prepared and incorporated in hydroxypropyl methylcellulose (HPMC) films under different conditions. Mechanical properties, water vapor and oxygen permeability, water solubility, and scanning and transmission electron microscopy (SEM and TEM) results were analyzed. Incorporation of chitosan nanoparticles in the films improved their mechanical properties significantly, while also improving film barrier properties significantly. The chitosan poly(methacrylic acid) (CS-PMAA) nanoparticles tend to occupy the empty spaces in the pores of the HPMC matrix, inducing the collapse of the pores and thereby improving film tensile and barrier properties. This study is the first to investigate the use of nanoparticles for the purpose of strengthening HPMC films.     

Water Vapor Permeability of Whey Protein Emulsion Films as Affected by pH

The water vapor permeability (WVP) of whey protein isolate-beeswax emulsion films was investigated as related to pH. Lower WVP was observed for films cast from solutions at pH 7.0. When pH of the film-forming solution was lowered, resulting film WVP increased. At the isoelectric point, WVP was the highest. As pH of the emulsion approached pI, a sharp change in viscosity occurred due to an increase in protein aggregation. This increase in viscosity probably lowered lipid mobility and reduced interconnectivity among lipid droplets, resulting in the higher WVP. For minimum WVP, such films should be applied at pH different from pI.