# Applications of Plant Polymer-Based Solid Foams: Current Trends in the Food Industry
## 2 Food Industry Applications
### Plant Polymer-Based Foams as Edible Materials
#### 2.1.6 Plant Polymer-Based Egg Protein Replacers  
In aerated foods such as meringues, marshallow, bread, cakes, and soutfles, foams are responsible for the appropriate textures and a particular mouthfeeal because of the little air bubbles trapped in the food system [1]. This is a complex process, where different physicochemical interactions and processing conditions play crucial roles to achieve the appropriate foamy structure. Polymer functional properties (foaming capacity and stability, as well as emulsification) are critical to achieve a solid foam-like structure. That is why egg proteins are important ingredients in the bakery industry and the main goal when using other polymers as substitutes is to replicate their functionalities because replacers influence the textural and physical properties of the final product. Several studies have been carried out using whey protein to prepare meringue and there has been an extensive gain of knowledge in the understanding of its rheology and surface properties, as shown by the works of [PERSON] and [PERSON] [17] and [PERSON], [PERSON], [PERSON], [PERSON] [69; 70]. However, in the field of plant polymers, finding substitutes for egg proteins as foaming agents is not an easy task, though some advances have been made. For example, soapwort extract can be used to partially replace egg white proteins (EWP) as a foaming agent in sponge cake formulations. Rheological and physical properties of cake batters and physical and sensory properties of sponge cakes were analyzed to determine the effects of soapwort extract addition. Different formulations were produced replacing egg white proteins with soapwort extract by 25%, 50%, and 75% on weight basis. Replacement of the protein source up to 75% did not have a significant effect on the specific gravity of batters (\(p>0.05\)). Likewise, the flow behavior indices (\(n\)) and the consistency indices (k) of cake batters were not affected by the addition of soapwort extract. Sponin content in the soapwort extract and saponin chemical structure containing polar (water-soluble side chains) and nonpolar (sapogenin) molecules facilitate incorporation of air into the batter. Additionally, physical properties of sponge cakes were not altered either. Regarding the sensory properties of sponge cakes, the results were also favorable. Sponge cakes formulated with 50% and 75% soapwort extract on weight basis received significantly higher chewiness scores than control cakes (\(p<0.05\)) [37]. Likewise, lentil protein can totally or partially substitute egg and milk protein as a foaming and stabilizer agent in angel food cake, resulting in products with satisfactory quality [42]. In this study, increasing the amount of lentil protein will increase the viscosity of the batter due to the more entangled lentil protein structure at higher protein concentrations, which might help air retention in the aerated system. Less air escaped from the lentil protein-based foamy batter than the control during baking, probably due to the formation of strong networks around the air cells that prevented microstructure collapse during gas expansion when the wet foam was transformed into solid foam. Additionally, the mean