# 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
Based on the results above, the cassava starch-based foams might be a promising biodegradable material to be used for solid food packaging, and future research should focus on the improvement of their physicochemical and structural properties [59]. In the study by [PERSON] et al. [60], new biodegradable trays were produced based on the blend of cassava starch with sugarcane bagasse. This mixture was then blended with different fibrous agro-industrial residues, such as cornhusk, malt bagasse, and orange bagasse. Trays produced from those mixtures presented high water sorption during storage under high or medium relative humidity. They were also more rigid and more susceptible to degradation than EPS trays. FTIR analysis revealed that hydrogen bonding between cassava starch and the other biodegradable tray components may have occurred during processing, as well as water interaction with other formulation components (starch, glycerol, and fibers). SEM micrographs showed that fibers of the residues were incorporated into the starch matrix and well distributed, making the material homogeneous, which contributed to good mechanical properties. As a result, the combination of cassava starch, sugarcane bagasse, and cornhusk was shown to be the better mix. In the works by [PERSON] et al. [61] and [PERSON] et al. [62], biodegradable trays were developed based on cassava starch and organically modified montmorillonite, called Closite(r)10A and 30B, using a baking process. They studied the changes on the microstructural and physicochemical properties of the trays when using the modified montmorillonite. Foams had the typical sandwich-type structure of the foams made by thermopressing. This structure includes dense outer skins that enclose small cells, similar to other foams made with cassava starch, as seen above. The interior of the foams had large cells with thin walls. Samples produced with the nanoclays showed larger air cells than the control sample. In the samples produced with sugarcane fiber, distribution of these fibers in the foam structure was homogeneous up to a concentration of 20 g fiber/100 g formulation. The density values were not affected by the addition of nanoclays. Probably, the addition of the nanoclays improved the foaming ability of starch pastes, resulting in the greater resistance of cell walls against collapse during the water evaporation that occurred during the baking process, as well as producing more thick trays. Results showed well-shaped foam trays with lower water absorption when using nanoclays in the formulations than using starch alone. The foam densities were between 0.2809 and 0.3075 g/cm\({}^{3}\). There were no dimensional changes during storage in the trays at all RH conditions tested, but no explanation was given to this phenomenon. The trays potentially resulted in an alternative packaging option for foods with low water content. Oca (_Oxalis tuberosa_) represents a novel starch source. In the work of [PERSON] et al. [64], sugarcane bagasse (SB) and asparagus peel fiber (AP) were mixed with oca starch to produce baked foams. The structure of foams reinforced with SB fiber (starch/fiber ratio of 95/5), AP fiber (95/5) and without addition of fiber (100/0) was heterogeneous. The fiber distribution through the cellulose matrix was dissimilar for both SB and AP fiber. Trays with SB fiber had larger cells arranged in a thinner layer than those with AP fiber, which was probably due to less interference with starch expansion during thermoforming of the tray. Both exhibited the typical sandwich structure.