Effects of glycerol content and film thickness on the properties of vital wheat gluten films cast at pH 4 and 11

• Published in: Journal of applied polymer science 2010-09, Vol.117 (6), p.3506-3514
• Main Authors: Cho, S.-W., Gällstedt, M., Hedenqvist, M. S.
• Format: Article
• Language: English
• Subjects: Applied sciences; Biopolymers; Contact; Diffusion; Energi och material; Exact sciences and technology; Forms of application and semi-finished materials; Gluten; Glycerols; Optical properties; Polymer industry, paints, wood; Proteins; Sheets and films; Technology of polymers; Thick films; Thin films; Transparency; Wheat
• ISSN: 0021-8995; 1097-4628; 1097-4628
• DOI: 10.1002/app.32235

This study deals with the optical properties and plasticizer migration properties of vital wheat gluten (WG) films cast at pH 4 and 11. The films contained initially 8, 16, and 25 wt % glycerol and were aged at 23°C and 50% relative humidity for at least 17 weeks on a paper support to simulate a situation where a paper packaging is laminated with an oxygen barrier film of WG. The films, having target thicknesses of 50 and 250 μm, were characterized visually and with ultraviolet/visible and infrared spectroscopy; the mass loss was measured by gravimetry or by a glycerol‐specific gas chromatography method. The thin films produced at pH 4 were, in general, more heterogeneous than those produced at pH 11. The thin pH 4 films consisted of transparent regions surrounding beige glycerol‐rich regions, the former probably rich in gliadin and the latter rich in glutenin. This, together with less Maillard browning, meant that the thin pH 4 films, in contrast to the more homogeneous (beige) thin pH 11 films, showed good contact clarity. The variations in glycerol content did not significantly change the optical properties of the films. All the films showed a significant loss of glycerol to the paper support but, after almost 9 months, the thick pH 11 film containing initially 25 wt % glycerol was still very flexible and, despite a better contact to the paper, had a higher residual glycerol content than the pH 4 film, which was also more brittle. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010