Abstract/Summary

Conventional plastic packaging is almost non-degradable, leading to significant environmental concerns. As a result, developing biodegradable packaging materials has attracted considerable attention from both industry and researchers. This study explores the potential of hordein, a protein extracted from spent barley, as a biodegradable packaging material. The high glutamine content and presence of hydrophobic amino acids, such as proline, leucine, and valine, endow hordein with strong aggregation properties and notable hydrophobicity. However, hordein-based films tend to have poor mechanical properties. Therefore, addition of individual plasticizers, glycerol (GLY) and PEG400 and their combinations were investigated in this research in order to enhance its property. The composite plasticizer formed by 25% PEG and 75% GLY demonstrated a synergistic effect, and significantly improved tensile strength and elongation at break of hordein film. Furthermore, the optical property of hordein film was also optimized in this research. Heat treatment was able to unfold the protein structure, exposing thiol groups to promote cross-linking through disulfide bonds and strengthening the protein network. Similarly, transglutaminase (TGase) could induce covalent cross-linking by forming isopeptide bonds between glutamine and lysine residues. To further enhance the mechanical properties of the hordein films, heat treatment at 85oC for 30 mins and TGase added at 0, 10, 20, 30 and 40 U/g were applied to assess their impacts on hordein film quality. Heat treatment produced a thinner film without compromising its mechanical property, while 20 U/g TGase achieved optimal mechanical properties. Although improvements were observed, the mechanical properties still fell short of currently used competing alternatives. Given hordein's excellent hydrophobicity and UV-blocking properties, the possibility of using hordein as a supplementary ingredient to enhance the properties of starch-based films was explored in this work. Starch films tend to be inherently brittle and sensitive to moisture, despite their superior film-forming ability. Corn starch was identified as the optimal base material for film production, outperforming potato and wheat starch in comparative analyses. Hordein was incorporated into the corn starch matrix at varying Abstract 10 mass ratios (10%, 20%, 30% and 40%) to assess its effect on the properties of starch film. The results showed that the addition of hordein significantly increased film thickness, tensile strength (TS), and UV-blocking performance of starch film. Overall, this study provides valuable insights into the characteristics of hordein and its potential application in the development of biodegradable food packaging films, offering a promising alternative to conventional plastic materials.