چكيده انگليسي :
Many valuable food products, such as chicken meat, have a short shelf life at refrigerated temperatures due to their high moisture and protein contents that provide a suitable environment for microbial growth. Therefore, controlling the cold chain during the transportation and sale is critical to prevent economic losses for producers and ensure food safety and quality for consumers. For this purpose, thermal insulation packaging plays a very important role in protecting food products from external factors, especially temperature flactuation, as one of the most important factors affecting product’s quality. One of the advanced insulation materials is aerogel. The main reason for the low thermal conductivity of these nanomaterials is their porous structure. The pores in their structure prevent continuous heat transfer. Nowadays, protein-based aerogels have received more attention due to their biocompatibility, biodegradability, and non-toxicity. Egg white powder (EWP) possesses a high demand globally due to its ease of transportation and convenient storage compared to fresh eggs. However, hydrated EWP has low solubility and shows aggregation, which limits its application. Therefore, high-intensity ultrasound (HIUS) and dielectric barrier discharge (DBD) plasma were used as new, non-thermal technologies to modify EWP. Aerogels obtained from egg white protein were flat with large pore sizes and were brittle. Therefore, in this study, the formation of complexes through electrostatic and hydrophobic interactions was studied. The resulting complexes have potentially better performance such as rheology, gelation, and interfacial properties compared to the protein and polysaccharide alone. EWP was modified using HIUS with powers of 100, 200, and 300 W, and DBD plasma with intensities of 16, 18, and 20 kV. Then, the effects of the treatments on structural changes, physicochemical properties, and functional characteristics of the protein were analyzed. The results showed that the treatments increased the surface hydrophobicity and zeta potential and significantly reduced the particle size and surface tension (P < 0.05). The structural changes and physicochemical properties led to improved foaming and emulsifying properties of the samples. Egg white protein treated with ultrasound at 300 W and plasma at 20 kV with a concentration of 10% were selected as the best samples for the production of binary hydrogels using 0.5% xanthan gum in different ratios (0:5, 4:1, 3:2, 2:3, 1:4 and 0:5). Analysis of the rheological properties of the hydrogels showed that ultrasound and plasma treatments reduced the apparent viscosity of the solutions and increased the storage modulus of the hydrogels. In addition, the treatments increased the water holding capacity and stiffness of the samples. Increasing the gum ratio led to an increase in the viscosity of the solutions, an increase in the loss modulus, an increase in the water holding capacity, and a decrease in the stiffness of the hydrogels. After examining the properties of hydrogels, aerogels were obtained using the freeze-drying method, and their properties such as bulk density, true density, porosity, thermal conductivity, mechanical strength, and morphology were investigated. The results showed that due to ultrasound, plasma, and increasing the ratio of xanthan gum, density, thermal conductivity, pore size, and elastic modulus decrease, and porosity increases. Based on the analysis using the response surface method, an egg white protein sample treated with 20 kV plasma and a protein-to-gum ratio of 0.4:6.6 was selected as the optimal aerogel and in addition to physical, morphological, and chemical structure properties, water vapor absorption properties, specific surface area, average pore size, thermal stability, and thermal properties were also investigated.
