Viscoelastic Flow of Plant Protein Melts under High Moisture Extrusion Conditions
| Autor: | Stirnemann, Eric |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2022 |
| Předmět: | |
| DOI: | 10.3929/ethz-b-000569239 |
| Popis: | Protein is an essential part of our diet and is often consumed in the form of animal products. Raising animals for food emits large amounts of greenhouse gases and is an inefficient way of converting plant protein into food. A less resourceintensive protein supply is needed, to feed a growing population adequately and sustainably. Therefore, an increasing number of consumers choose plant-based meat analogs over traditional animal meat. Appealing plant-based meat analogs can be produced by high-moisture extrusion cooking (HMEC), a continuous processing method that texturizes proteins to form fibrous, meat-like structures. As an emerging technology, HMEC has the potential to skip the animal and change the way we produce meat. Plant proteins are hydrated and heated in the extruder to form a melt with a characteristic viscoelastic flow behavior. The flow into the cooling die combines shear and elongational flow and is largely defining the fiber structure of the extrudate. Understanding the rheological behavior of the material is key to control and improve the product properties. However, HMEC is largely still a black box and transient conditions in the extruder cannot be observed well. In addition, the raw material requirements and the relationship between process and product properties for plant proteins other than soy are so far not well understood. To diversify the input protein sources for HMEC and investigate the structure formation in HMEC, this work explored 1) The plant protein characteristics required for high-moisture extrusion applications, 2) The relationships between process settings and product properties, and 3) The viscous and elastic properties of plant protein melts at high moisture (45-60%) and high temperature (90-150℃) conditions under elevated pressure (5-40bars). Characterization of functional properties of commercial pea, sunflower, and soy proteins has shown that, even though the parameters like protein content, water holding capacity, and solubility of different products are comparable, the viscosities can differ by an order of magnitude. Hence, the viscosity is a key property to select raw materials. Extrusion trials were conducted on lab and pilot-scale extruders with a modular cooling die and adjustable die entry. Narrowing the die entry led to a reduction of a characteristic "flow layer" length and a lower cutting strength of the extrudate. Increasing the length of the cooling die or reducing its temperature led to higher die entry pressure and therefore a more strongly shear-determined parabolic flow profile. Two specific measuring dies were engineered to quantify rheological parameters of the melt in-line during the extrusion process. Compared to high-pressure capillary and commercially available in-line rheometers, the new dies allowed improved measure of protein melts at authentic HMEC conditions without flash evaporation of the water. The tiered rheometer die enabled us to measure multiple shear rates serially and thereby deriving and applying rheological flow corrections of the non-Newtonian flow behavior. The second measuring die, with a feature to measure normal stress differences via the so-called ‘hole-effect’, allowed to quantify the first and second normal stress differences. The in-line rheological measurements demonstrated that the transient melt state of the materials was shear and elongational thinning as well as viscoelastic. The first normal stress difference showed to be higher by a factor of 1.5-2 than the second normal stress difference and as expected both numbers increased for higher shear stresses. This thesis lays the foundation to better characterize the rheological behavior of a diverse set of plant protein raw materials and therefore provides a base for tailoring plant-based products to match consumers’ needs. Through the new measuring techniques, the impact of specific process settings on the rheological properties were investigated. Rheological characterization of different raw materials will allow linking the raw material properties with the final properties of the extrudate. The determination of true rheological parameters of plant protein melts at HMEC conditions is a key requirement for future cooling die design and representative computational fluid dynamics (CFD) simulations. Food Process Engineering series, 89 ISBN:978-3-905609-98-1 |
| Databáze: | OpenAIRE |
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