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Heat-induced protein gels are appreciated due to their texture in a variety of food products. To support the shift to more sustainable protein consumption more knowledge is needed about plant protein gelation behavior and rheological properties of gels. In this study, the effect of calcium concentration (10 mM–100 mM) and pH (5.9–6.8) on heat-induced gelation behavior of 10 w/w% pea protein water-soluble extract separated from a commercial pea protein isolate (WSE-PPI) were for the first time investigated and compared. The rheological results show Gʹ values of around 3000 Pa for gels containing 20 mM calcium, and then a decrease in Gʹ by a factor ∼1.3 when the calcium concentration increased to 100 mM, whereas a continuous increase in gel strength was observed with the pH decrease of WSE-PPI dispersions. By comparison of calcium-addition and pH-adjusted heat-induced gels at the same pH, it was found that at low calcium concentrations (≤20 mM), the calcium-assisted gels exhibited higher gel strength. Contrariwise, at high calcium concentrations (≥50 mM), the pH-adjusted gels have higher gel stiffness and larger deformability before rupture. CLSM results verified this finding and show that the gel structure of pH-adjusted gels are more homogenous, containing significantly more compact structure. Overall, our findings show a systematic link between microstructure and rheological properties of heat-induced gels, which can be controlled by the calcium addition and pH adjustment. These results provide valuable information for the modulation, design, and customization of plant derived protein gels for specific food applications.

Over the past decades, three-dimensional (3D) printing has received a great level of attention for its potential advantages over traditional processing in personalized food production and customized design. The food material properties and characteristics are essential for the printability of the final product. The food ink must be able to be extruded easily through a nozzle and the prepared formulation must possess certain properties before printing that ensure structure accuracy and shape-stability during and after the printing process. However, current 3D printing technology has a strict requirement on the rheological properties of food materials. To estimate printability, rheological properties of the food ink should be determined and studied. The main aim of this thesis work is to investigate the 3D printability of citrus side-stream powder based gels formulated from principally orange powder (OP), but also lemon powder (LP) from the food industry. The elaboration and composition impact on the mechanical and structural properties of the food ink by varying the temperature of processing and milli-Q water volume addition was also studied. Besides, any physico-chemical change on the final 3D extruded structure induced by the variation of the extrusion nozzle diameter along the printing process was analysed. An evaluation of the rheological properties of the OP-based gels was additionally carried out through flow and amplitude sweep tests. The type of side-stream, its powder concentration, the milli-Q water volume added and the temperature of the thermal processing had a significant impact on the behaviour of the final OP-based gels printability and rheological properties, indicating that the number of factors that can affect the variability of the 3D printing process and food systems were elevated. Besides, the extrusion nozzle diameter variation remarkably aff

Self-diffusion NMR is used to investigate monodispersed oil in water emulsions and the subsequent gel formed by removing the water through evaporation. The radius of the oil droplets in the emulsions is measured using a number of diffusion methods based on the measurement of the mean squared displacement of the oil, water, and tracer molecules. The results are consistent with the known size of the emulsions. Bragg-like reflections due to the restricted diffusion of the water around the oil droplets are observed due to the low polydispersity of the emulsions and the dense packing. The resulting data are fitted to a pore glass model to give the diameter of both the pools of interstitial water and the oil droplets. In the gel, information on the residual three-dimensional structure is obtained using the short time behavior of the effective diffusion coefficient to give the surface to volume ratio of the residual protein network structure. The values for the surface to volume ratio are found to be consistent with the expected increase of the surface area of monodisperse droplets forming a gel network. At long diffusion observation times, the permeability of the network structure is investigated by diffusion NMR to give a complete picture of the colloidal system considered.