Abstract
This paper presents a novel approach to reduce the water vapor transmission rate (WVTR) and water absorbance of wheat gluten/paperboard laminates by introducing a hydrophobic component (oleic acid (OA)) into the hydrophilic plasticizer (glycerol). Whereas the paperboard showed immeasurably high WVTR, the laminate with gluten/glycerol yielded finite values. More importantly, by incorporating 75 wt.% OA into the plasticizer, the WVTR and water absorbance were reduced by, respectively, a factor of three and 1.5–2. Of particular interest was that the mechanical properties were not changing dramatically between 0 and 50 wt.% OA. The results showed clear benefits of combining a gluten film with paperboard. Whereas the paperboard provided toughness, the WG layer contributed with improved moisture barrier properties. In addition, WVTR indicated that the paperboard reduced the swelling of the outer gluten/glycerol layer in moist conditions; a free standing gluten/glycerol film would yield infinite, rather than finite, WVTR values.
Highlights
Wheat gluten (WG) is an interesting alternative to petroleum-based polymeric materials [1] and is available in large quantities as a byproduct from the wheat starch industry [2]
The specific water vapor transmission rate decreased with increasing amount of oleic acid in the glycerol/oleic acid mixture (Table 1)
Smaller values would be obtained if the water vapor transmission rate (WVTR) values were instead normalized with the WG layer thickness, neglecting the paperboard, which did not contribute to the barrier properties
Summary
Wheat gluten (WG) is an interesting alternative to petroleum-based polymeric materials [1] and is available in large quantities as a byproduct from the wheat starch industry [2]. Paperboard coatings for food packaging applications are commonly made from petroleum-based polymers. These coatings are essential for the lifetime of the food products as they act as oxygen and/or water/water vapor barriers [8]. Since wheat gluten is able to form films [1] and has a low oxygen permeability (OP) under dry conditions [9], it is interesting as an alternative in environment-friendly edible and nonedible films for paperboards in food packaging [8]. The fact that wheat gluten is hydrophilic and has a high water permeability limits its uses; an effective control of moisture transfer is essential for most foods [10]
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