How to formulate for structure and texture via 3D-printing: Design and characterisation of edible and printable feedstock - dairy gels

Daffner, Kilian Josef (2021). How to formulate for structure and texture via 3D-printing: Design and characterisation of edible and printable feedstock - dairy gels. University of Birmingham. Ph.D.

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Abstract

3D-printing of food is a novel and promising technology capable of creating individualised foods differing in composition, texture, taste or shape. Objects are created layer-by-layer and the most common additive manufacturing technique for food relies on an extrusion process. In order to formulate for structure and texture of food objects via a printing process, in-depth understanding of the solidification mechanism and the material properties is of highest importance. While most of the current research on extrusion printing focuses on pastes and gels, which maintain their shape due to a yield stress, the key challenge of this work lies in a fast, local and irreversible transition of the feedstock from a solution (sol) to a gel. High dairy protein-based materials, which offer health benefits and have high satiating effects, were used to create and tailor novel edible formulations for applications in thermal extrusion printing.

First, characterisation of a solidification mechanism suitable for thermal printing of high dairy protein-based feedstock including a fast sol−gel transition was conducted. Investigation of the pH−temperature (T)-route, cold acidification followed by heating, on the rheometer provided evidence that the temperature–time profile used to trigger gelation was comparable to 3D-print-ing but without superimposed flow. The sol–gel transition temperature as determined by rheology was used to mimic dynamic conditions during printing by applying a steep temperature gradient. Firm gels were produced and classified regarding their physical properties and status around the sol–gel transition. Formulations showing preferable characteristics, including a low storage modulus G’ (~ 0.1 Pa) at low temperatures (2°C) followed by a steep increase of G’ during sol–gel transition, were considered to be suitable feedstock for applications in thermal extrusion 3D-printing.

Second, the two main dairy proteins (micellar casein and whey protein) were combined to create and to tailor novel edible casein−whey protein suspensions. These formulations were characterised regarding their potential use for extrusion-based 3D-printing and several design rules
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were established. Sol−characteristics at low temperature (2°C) were confirmed, providing a liquid feedstock which could be transferred into a gel via the pH−T-route. The pH at heating during denaturation of the whey proteins as well as the overall protein content were crucial parameters to change the microstructure of casein−whey protein suspensions, e.g. resulting in unwanted pre−gelation (G’ > 1 Pa) at too high protein contents. Formulations with depleted casein micelles (CM), caused by desired dissociation of κ-casein at increased pH at heating, showed lower sol−gel transition temperatures and increased aggregation rates. The aggregation rate (represented by the storage modulus G’) was proposed as a first good indicator for the printability of high dairy protein-based formulations.

Furthermore, for the creation of more complex and novel edible formulations, dairy fat was added to casein−whey protein suspensions. The additional product parameter, fat, changed the microstructure as the overall total solid content of the formulations increased. Mechanical treatment was necessary to obtain smaller milk fat particles (< 1 μm) covered with protein, which could mimic the protein behaviour and actively contribute as pseudo-proteins to the gelation process via the pH−T-route. With increasing pH at heating, more depleted casein micelles were found on the surface of mechanically treated fat globules, causing a decrease in the sol−gel transition temperature and an increase in the aggregation rate. At a higher pH at heating, more particles contributed to the gelation per unit area and the surface properties of the fat globules covered with certain proteins, e.g. κ-casein depleted CM, were favourable, shown via electrophoresis and a newly developed protocol for low dose transmission electron cryogenic micros-copy. Several protein−fat formulations with promising aggregation rates could be printed.

Overall, this thesis demonstrates that high dairy protein-based formulations with and without additional fat can be used as a novel feedstock for thermal extrusion 3D-printing applications via the pH−T-route, if product- and process parameters are precisely adjusted, and all the established design rules are adhered to.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):