# Applications of Plant Polymer-Based Solid Foams: Current Trends in the Food Industry
## 2 Food Industry Applications
### Plant Polymer-Based Foams as Food Packaging Materials
#### 2.2.1 Starch
Thus, the direct interactions and the proximity between starch chains reduced, while free volume between these molecules increased. Under tensile forces, movements of starch chains were facilitated, and this is reflected in the decrease of the mechanical strength of materials. The sorption isotherm data demonstrated that the inclusion of malt bagasse at 10% (\(w/w\)) resulted in a reduction in water absorption of starch foams. Cassava starch trays with malt bagasse might, therefore, be a fitting alternative for packing solid foods. In another similar study, [PERSON] et al. [57] added sesame cake to cassava starch to produce foams and evaluated the effects on the morphological, physical, and mechanical properties of the materials produced. The content of sesame cake added ranged from 0% to 40% (\(w/w\)). Cassava starch-based foams incorporated with sesame cake exhibited improved mechanical properties and reduced density and water capacity absorption when compared to starch control foams. Using sesame cake (SC) concentrations higher than 20% showed better mechanical properties than commercial expanded polystyrene (EPS). Foams produced in this study showed a decrease in flexural stress and modulus of elasticity with the addition of SC. The reduction of these properties correlates with their lower density and larger cells in inner structure in comparison to control foams. Large cells in the foam's inner structure and thinner walls can be associated with water evaporation and leakage through the mold, consequently causing cell rupture. Nevertheless, although enhancements in flexibility and moisture sensibility are still necessary, starch-based foams incorporated with sesame cake might be an alternative for packing solid foods and foods with low moisture content. Another biodegradable cassava starch-based foam produced by thermal expansion was developed by [PERSON] et al. [58], who incorporated grape stalks and evaluated the morphology (SEM), chemical structure (FTIR), crystallinity (XRD), biodegradability, and applicability for food storage. Foams exhibited sandwich-type structure with denser outer skins that enclose small cells, whereas the inner structure was less dense with large cells. The material also showed good expansion, which might be the result of the occurrence of hydrogen bond-like interactions between the components of the expanded structure during processing of the foam. Biodegradability tests demonstrated neither formation of -recalcitrant compounds nor structural alterations that would hinder foam degradation. Foams were completely biodegradable after seven weeks. Additionally, foams made with cassava starch with grape stalks added showed a promising application in the packaging of foods with a low moisture content. Cassava starch, in combination with pineapple shell, was also utilized as a strengthening material to manufacture biodegradable foam trays by a compression molding process. The starch/fiber ratios were varied to modulate the foam, microstructure and physical and mechanical properties. The foams showed a good distribution of the pineapple shell fiber throughout the polymeric matrix and a semi-crystalline structure. Even though all reinforced foams showed high water absorption, foams produced at a starch/fiber ratio of 95/5 showed the lowest values of thickness and density (2.58 mm and 367 kg m\({}^{-3}\), respectively) and the highest crystallinity index value. This starch/fiber ratio also led to foam trays with tensile strengths similar to those of expanded polystyrene samples. This is likely due to the reinforcing effect of the interfacial interaction between the fiber and the starch matrix. However, high proportions of fiber can interfere with the expansibility and produce discontinuity in the starch matrix. An increase in the fiber concentration weakened interactions among starch chains due to a lower proportion of starch in the composites.