Application of Pickering emulsion stabilized with soy protein nanoparticles in the formulation of gluten-free cake and evalu-ation of its quality indicators

Introduction: Nowadays, with the development of technology, following an appropriate diet is of great importance, and different people go on various diets. Moreover, some food intolerance cause people to change their diets inevitably, with celiac disease being one of them. In celiac, which is an autoimmune and hereditary disease, the mucosal mem-brane of the pa-tient small intestine is damaged and inflamed after the consumption of gluten-containing cereal-based products. Accordingly, Rice flour is typically used in the production of gluten-free cake, and given the qualitative defects of gluten-free products, gluten substitutes should be employed. Application of Pickering emulsion (PE) is a way of enhancing the properties viscoelastic of cake. Nowadays, the research about the use of emulsion in the structure of gluten-free products has been expanded to improve its quality features. According to this, one of the practical applications gluten-free food products are important for individuals with celiac disease or gluten-related disorders since they need to follow a strict gluten-free diet. This study provides information on a Pickering emulsion stabilized by soy protein nanoparticles use to boost the physical properties of gluten-free cake batter. Results showed that use of these additives improved the techno-functional properties of the gluten-free cake batter. Therefore, the findings of this study can be use-ful for the production of functional free-gluten food products with health-promoting at-tributes. The aim of this research was to use Pickering emulsion (PE) stabilized by soy protein nanoparticles and xanthan gum in gluten-free cake dough based on Rice flour and monitor its quality indicators during shelf life. Considering the studies conducted so far, PE based on plant proteins like soy protein and microbial polysaccharides like xanthan, has not ever been reported in the preparation of gluten-free cake. Therefore, the purpose of this research is to stabilize PE by soy protein nanoparticles (SPNs), as well as investi-gating its effects on gluten-free rice flour-based cake and evaluation of its quality indica-tors during shelf life.
Material and methods: In this study, Pickering emulsion was prepared from soy protein nanoparticles and xanthan solution 0.1% (w/v). For this purpose, sunflower oil (20%) was gently added to the mixture of xanthan solution (20%) and SPNs (60%), which was sub-sequently agitated using a homogenizer at 11000 rpm. Next, the intrinsic properties of emulsion such as hydrodynamic diameter, polydispersity index (PDI) zeta potential, and creaming index of the SPNs and the PE were measured. Furthermore, the emulsifying activity (EA) test was performed according to the method presented by Dalev & Sime-onova (1995) with slight changes. Finally, the qualitative and viscoelastic properties of gluten-free cake-containing emulsion were investigated in comparison with the control sample during shelf life.
Results and discussion: The results of this research showed that the presence of soy pro-tein nanoparticles along with xanthan gum caused stability, proper dispersion index, ho-mogeneity of particles, and determining the electrical state of the surface of particles in PE. In fact, the prepared PE had an acceptable dispersity, because the lower the PDI is, the more suitable the dispersity is, and the more homogenous the particles are. The zeta potentials of the SPNs and the PE were equal to -13.166 and -30.696 mV, respectively. The high zeta potential of colloidal particles causes an increase in electrostatic repulsive forces between them, thus raising the system physical stability at pH values above its isoe-lectric point. On the other hand, the emulsion prepared using the SPNs and the xanthan solution showed a higher zeta potential. Generally, xanthan solution is negatively charged at neutral pH, due to the occurrence of acidic groups in the structure of this gum. The presence of negative charge in both the SPNs and the gum elevated the zeta potential of the emulsion. The ability of the emulsion to resist the changes during three weeks showed insignificant phase separation and also with 78% emulsion activity. In addition, the pres-ence of PE (20 mL/100g rice flour) in the formulation of gluten-free cake dough im-proved the viscoelastic properties and quality of the final product during the shelf life of one week. In fact, considering the capability and usage of these emulsions in the food industry, especially the bakery industry, it improved the quality characteristics of cake products for the consumer, such as the specific volume and porosity of the cake, its tex-ture strength, and its shelf life. Pickering emulsion increased the moisture content in the cake, which had a positive effect on the hardness of the sample. Whereas, the volume and porosity decreased in the cake containing Pickering emulsion. On the other hand, the col-or of the sample was better maintained over time by adding emulsion during shelf life.
Conclusion: Based on the results of this research, SPNs improved the PE stability. Fur-thermore, xanthan gum inhibited the aggregation of the oil droplets by increasing the PE consistency and forming a network in the emulsion. The presence of PE in the gluten-free cake batter formulation caused a relative decrease in volume and porosity compared to the control sample by creating a coherent and uniform structure. By maintaining more moisture during the storage period, PE had much better viscoelastic and color characteris-tics compared to the control sample.