R.F. Testin

Mechanical and Barrier Properties of Edible Corn and Wheat Protein Films

ABSTRACTPublished methods for production of homogeneous edible films from com and wheat proteins were adapted. Barrier and mechanical properties of the edible films were evaluated with procedures commonly used on polymeric films. Mechanical property data included thickness, elongation, tensile strength, tear strength, and burst strength measurements. Barrier property data included water vapor, oxygen, and carbon dioxide gas transmission rate measurements. Homogeneous com and wheat protein films were found to have low tensile strengths, far less than cellophane. Com films were brittle while wheat films were elastic in comparison to cellophane. All three types of film had low permeabilities for dry gases but relatively high water vapor permeabilities.

Property Modification of Edible Wheat, Gluten-based Films

Procedures were developed to produce edible wheat, gluten-based films. A film was produced as a standard. Five additional films were then produced by modifying the initial film-forming solution. Modifications included changing the plasticizer, partially substituting wheat gluten with soy protein isolate and corn zein, and incorporating two acetylated monoglyceride products. All films were characterized by measuring selected mechanical properties, and permeabilities to water vapor and to oxygen. Comparison of the films, in terms of their measured properties, indicates ways to improve the overall performance of the standard film as a potential packaging material. A main limitation of all of the films was their poor water vapor barrier characteristics. On the other hand, they were very good oxygen barriers. All modified films were stronger than the standard in terms of tensile and bursting strength. The film containing soy protein was the strongest and the most uniform. Significant differences in measured properties were observed when the plasticizer was changed from glycerin to triethylene glycol.

Water vapor transport parameters of a cast wheat gluten film

Understanding the mode of transport of water vapor through the film is important for improv ing the moisture barrier properties of wheat gluten (WG) films. Effective permeability ( P eff ), solubility (S eff ), and diffusion (D eff ) coefficients of a hydrophilic cast WG film were determined at 25°C within the relative humidity (RH) range of 0–84% (with a 9–13% RH gradient between upstream and downstream water vapor flux). P eff , S eff , and D eff increased substantially as the RH gradient moved upwards in the RH spectrum. P eff increased by four orders of magnitude from the lowest RH condition of 0–11% (3.8×10 −11 g·m/m 2 ·s·Pa) to the highest RH condition of 75–84% (4.1×10 −7 g·m/m 2 ·s·Pa). A moisture sorption isotherm of the film at 25°C was constructed. Both the Guggen heim–Anderson–DeBoer (GAB) and the Kuhn moisture sorption isotherm models showed a good fit to the experimental adsorption data. Testing of WG films at the expected conditions of actual use is necessary to quantify the water vapor permeation through the films.

Water vapor permeability of wheat gluten and soy protein isolate films

Abstract Protein films were produced from wheat gluten and soy protein isolate. The water vapor permeability of the films was evaluated at 5, 15, 25 and 35°C and at 100-50% and 100-70% relative humidity gradients across the films. For all tested temperatures, estimated water vapor permeability constant values were greater at the 100-70% relative humidity gradient than at the 100-50% relative humidity gradient indicating a pressure dependence of the permeability constant. Similar behavior has been documented in the literature for other types of plastic and biopolymer hydrophilic films. Most likely, water sorption by the hydrophilic protein films was higher when the outer film surface was exposed to 70% rather than to 50% relative humidity. Increased sorbed water plasticized protein films facilitating water vapor permeation and yielding greater water vapor permeability constant values. At both tested relative humidity gradients over the studied temperature range, the water vapor permeability constant of the two protein films decreased with increasing temperature. This can also be explained by increases in water sorption and film plasticization, since water sorption by proteins is thermodynamically favored at lower temperatures.