# Applications of Plant Polymer-Based Solid Foams: Current Trends in the Food Industry
## 2 Food Industry Applications
### Plant Polymer-Based Foams as Edible Materials
#### 2.1.4 Gliadin and Lupin  
[PERSON] et al. [31] studied the impact of glycerol (Gly), linoleic acid (LA), and transglutaminase (SB6) in two concentrations (1-TG-Glia and 2-TG-Glia) as plasticizers on the development of gliadin (Glia) solid edible foams. Nanomorphology, studied by SAXS, indicated that Gly impaired the unfolding of gliadin in the foam; however, no statistically significant impact of the glycerol on gliadin polymerization within the foam was observed. In addition, there was a notable variation regarding bubble size distribution and a weakening effect on foam stabilization. However, if small pore sizes are desired in aerated food, there is a potential use for glycerol as an alternative to sugar, as well as the use of glycerol as a co-surfactant.  
The addition of linoleic acid (LA) in the foams caused the formation of an interrupted Glia network with large, sparsely located bubbles as revealed by X-ray tomograms. Overall, LA impacted gliadin polymerization and foam morphology by preventing the formation of S-S bonds and isopeptide bonds in the gliadin protein. The use of linolenic acid led to the formation of specific nanomorphologies in the foams, referred to as lamellar phases--a process that has been observed for the first time ever in this field of study. These processes suggest that the fortification of gliadin foam with linoleic acid, which is an essential fatty acid for humans, is possible in gliadin breakfast snack prototypes as a main ingredient to improve the nutritional profile of starch-rich foods, since those two components are \"compatible\" in structured foods.  
However, comparison of the non-treated gliadin foam (0-Glia) with the 2-TG-Glia (1.17 U/g) showed that an increase in the size of the bubbles as well as improved bubble spatial homogeneity occurred after a great cross-linking and polymerization of gliadins in the foam. This resulted in a well-developed protein matrix and foam morphology, in comparison to the other sets of foams composed of food dispersants. The study also suggests that SB6 may have played a role in gliadin folding and unfolding, probably because of the deamidation reaction.  
The results from this study showed that gliadin is a promising resource to create edible solid foams and has great foaming functionality.  
In a similar study, [PERSON] et al. [32] studied the impact of transglutaminases (TGs; SB6 and commercial), glycerol (Gly), soy lecithin (Lec) and linoleic acid (LA) on the micro- and nanostructure of solid foods for the creation of foams from LPI and fat blends that could be used to make aerated foods with an appealing texture. As in the previous study, 3-D tomographic images of LPI with TG revealed that SB6 contributed to an exceptional bubble spatial organization. Thus, SB6 significantly contributes to the foam's homogeneous periodic morphology. However, due to spray-drying preparation of Lupin, transglutaminases have limited influence on further cross-linking of the proteins. Nevertheless, the addition of lecithin promoted the formation of new hexagonal structures at the nanometric scale of the foam matrix, whereas linoleic acid contributed and led to the creation of lamellar structures and complex protein-lipid bonding at the nanometric and molecular range of the foam walls. Thus, both lecithin and linoleic acid generate less homogeneous foams.  
Results suggest that hydrophobic interactions between lupin proteins, which favor the development of a stable cross-linked matrix and thick matrix walls due to protein bond rupture and rearrangements, promote the formation of a relatively continuous surface. It has also been noted that both LA and LPI are compatible in forming stable layers. This is a result of great significance which may lead to many applications in the confectionery industry.  
As in the first study, glycerol produced a weakening effect on lupin foam stability, which might be associated with its effect on decreasing polymerization. Glycerol-Lupin foams were too brittle and unstable to withstand tomography and SEM analysis.