Investigating Shear Rheology of Plant Based Hipes and their Relevance to the Printability of Extrusion based 3D Printing
Creators: name: WANG, MINGHE
Publisher: name: University of Massachusetts Amherst
Year: 2024

The popularity of plant-based foods, particularly meat analogues, has increased significantly in recent years due to health concerns, environmental considerations, and animal welfare issues. High Internal Phase Emulsions (HIPEs) is the most promising material among different fat replacement materials due to its similar appearance, viscoelastic rheological properties and semi-solid structure. However, lots of studied focus on exploring the formulation of HIPEs. Only a few studies have investigated their processability in meat analogues. A promising technique for using HIPEs in food analogues is extrusion-based 3D printing, where the processability of the edible inks critically depends on their rheological properties. Therefore, this thesis investigated the shear rheology of plant-based HIPEs and their relevance to the printability of extrusion-based 3D printing. In this thesis, coconut oil-based HIPEs were chosen as the model for edible ink due to their resemblance in appearance and rheological properties to beef adipose tissue fat. Additionally, coconut oil-based HIPEs most closely replicated the textural properties of adipose tissues. However, the phase inversion (water in oil emulsion) was observed in previous research. The formulation of coconut oil HIPEs was modified by increasing the protein concentration to avoid the phase inversion problem. Following these adjustments, stable oil-in-water coconut oil HIPEs were produced. To deepen the understanding of the relationship between the rheological characteristics of HIPEs and their printability, rheology tests and extrusion simulations were conducted for HIPEs formulated with coconut oil HIPEs. The shear rheology of the coconut-based HIPEs was thoroughly investigated. Three different approaches were used to evaluate the apparent viscosity and yield stress of the HIPEs to overcome the challenges associated with semi-solid materials like HIPEs. Firstly, the apparent viscosity was investigated using a strain-controlled flow ramp, stress-controlled flow ramp, and Cox-Merz rule methods. Among these methods, the stress-controlled flow ramp method was the most sensitive. Subsequently, yield stress was investigated using the Herschel-Bulkley model fitting, stress sweep, and amplitude sweep methods. These three methods obtained consistent yield stress values. Given their shear-thinning properties and appropriate yield stress, HIPEs were suitable for use as edible inks in 3D printing applications. To further the understanding of the processability of the HIPEs, computational fluid dynamic simulations were used to investigate the relationship between the back pressure required to maintain a given flow rate. The detailed simulations allowed for a full examination of the flow and pressure field inside a syringe during the extrusion process. The velocity profile, pressure profile, shear-rate field and viscosity-field in the syringe were determined by the simulation result. The simulated back pressure was obtained. Additionally, thixotropic tests assessed the recovery capabilities of the HIPEs. Lastly, the relationship between the rheological properties of HIPEs and their processability was constructed through experimental results derived from extrudability tests. These results indicated some differences between the simulation result and experimental data. This difference could be attributed to additional factors such as extension rheology, material elasticity, and relaxation time, which should be incorporated into the simulation models. Understanding these dynamics was beneficial for optimizing HIPEs as edible inks in 3D printing processes.