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Encapsulation of pea protein in alginate matrix by coldset gelation method and use of the capsules in fruit juices

Narin, Ceren
Plant based proteins gained importance in recent years due to the increase in the awareness of healthy diet and the increase in the consumption of plant-based foods. However, some features of plant-based proteins like the undesirable odor and flavor affect the sensorial properties of food they are added in. Therefore, encapsulation of these proteins could be a good strategy to tackle with this problem. It is also important to design stable microcapsules which would remain intact in the food they are used. In this study, microcapsules were designed and evaluated in terms of physical and functional properties. The objective of this study is to design microcapsules (beads) consisting of pea protein isolate by using sodium alginate as the coating material and cold gelation method as the encapsulation technique and to investigate the effect of different alginate concentrations (1, 1.5 and 2%) and heating ( at 80ºC for 30 mins) of proteins on the protein content, encapsulation efficiency, particle size, bead stability and the morphology of the capsules. Additionally, TD-NMR relaxometry analysis was also conducted to observe the changes in the beads related to change in parameters. Spin-spin relaxation (T2) time measurements were conducted to extract information on the microstructure of the beads. Microcapsules were also added to the real fruit juices (melon and pomegranate) since the goal was to enhance to protein content of juices by masking the flavour through encapsulation. To understand the suspension behavior of the beads, pectin was added to the juices (melon and pomegranate) at different ratios (0.5 and 1%) and the effects of pectin on the rheological behavior of the juices were investigated. Effect of pectin on the rheological properties juices was also was investigated since it could affect the release of the proteins from the capsules. Beads formed with 1.5% alginate was found to have the highest particle size for both samples regardless of the heat treatment (p<0.05). Heat treatment significantly increased the particle size of the samples (p<0.05). Results showed that both heat treatment and change in alginate ratio did not have change the encapsulation efficiency significantly (p<0.05). Also, protein content of the beads significantly decreased with heat treatment (p<0.05). SEM images showed that both alginate ratio and heat treatment resulted in change of the surface morphology of the beads. NMR relaxometry results demonstrated that as alginate ratio increased, T2 relaxation time decreased and non-heated samples had longer T2 values. Denaturation of the proteins with heating had a direct effect on the mobility of the protons thus T2 values decreased. Difference in pectin ratio was found to affect the viscosity of the juices. As pectin ratio increased, viscosity of both juices increased significantly (p<0.05). Melon juice was found to be more suitable in terms of the increase in viscosity and release rate of beads in juices. Results indicated that as alginate ratio increased and pectin ratio decreased, release of pea protein from alginate beads significantly increased (p<0.05). Finally, heat treatment was found to be effective on the release of the protein from beads. It significantly increased the release rate of the core material. In overall, it was concluded that, alginate was a suitable coating to encapsulate pea protein isolate and increase the protein content of the juices. As a next step, sensorial analysis would be performed to test the flavor masking power of the capsules on the juices.