Interpretive Summary:
About one million tons of pectin are annually available from the residues of the U.S. beet sugar and fruit juice industries yet almost none is refined and utilized for food or non-food applications. Finding new utilities for this biodegradable polysaccharide is critical for the future sustainability of U.S. agribusiness. In this study, pectin films were compounded in combination with two other low-value biopolymers, fish skin gelatin or soybean flour proteins. The composite films made from these biopolymers showed a mechanical property as strong as petroleum-derived polyvinyl chloride or polystyrene polymers and are water insoluble, thus can be used as a packaging materials. Developing new uses for pectins will create more demand for pectic byproducts from sugar beet and citrus fruit processing and this will benefit growers and processors.

Technical Abstract:
Composite films were prepared from pectin and fish skin gelatin (FSG) or pectin and soybean flour protein (SFP). The inclusion of protein promoted molecular interactions, resulting in a well-organized homogeneous structure, as revealed by scanning electron microscopy and fracture-acoustic emission analysis. The resultant composites showed an increase in stiffness and strength, and a decrease in water solubility and water vapor transmission rate, in comparison with films cast from pectin alone. The composite films inherited the elastic nature of proteins, thus being more flexible than pectin only films. Treating the composite films with glutaraldehyde/methanol induced chemical cross-linking with the proteins and reduced the interstitial spaces among the macromolecules, and consequently, improved their mechanical properties and water resistance. Treating the protein-free pectin films with glutaraldehyde/methanol also improved the Young's modulus and tensile strength, but showed little effect on the water resistance, because the treatment only caused dehydration of the pectin films and the dehydration is reversible. The composite films were biodegradable and possessed moderate mechanical properties and a low water vapor transmission rate. Therefore, the films are considered to have potential in applications as packaging or coating materials for food or drug industries.