How to formulate for structure and texture via 3D-Printing – design and characterisation of edible biopolymer gels to act as release vehicles

Kamlow, Michael-Alex ORCID: 0000-0002-1602-6702 (2023). How to formulate for structure and texture via 3D-Printing – design and characterisation of edible biopolymer gels to act as release vehicles. University of Birmingham. Ph.D.

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Abstract

3D printing of edible materials has seen a surge of interest within the last decade. However, there exists a shortage of printable materials and the understanding of parameters that must be controlled to facilitate successful print jobs that are appealing to consumers and reproducible to prevent waste and keep costs down. 3D printed objects are created one layer at a time, with subsequent layers deposited on top of the previous one. This requires the shape to set quickly and be able to support the weight of the new layers above it. Most research on the 3D printing of edible materials has focused on extruding pre-gelled samples which maintain their shape due to yield stress, with no sol-gel transition taking place. This work aims to address the gaps in the literature present surrounding hot-extrusion 3D printing. Hydrocolloid gels that gel rapidly, with a high gel strength and recovery that allows it to maintain its shape after printing are ideal for this method. This work examined agar and kappa-carrageenan (кC) as candidate hydrocolloids.

Initially these gels had their thermal characteristics analysed through rheology and micro differential scanning calorimetry (DSC), as the gel temperatures were a key parameter for hot-extrusion 3D printing. The storage modulus (G′) was also used to determine printability of the gels. Above their gel temperature, gels should have a low G′ which should rapidly rise below the gel temperature. 3% w/v кC with 2% w/v vitamin B1 had a G′ of around 100,000 Pascals and was found to be printable. 2% w/v agar was not printable with the printing setup being used. Hereafter, agar was no longer used. Texture profile analysis showed that 3D printed gels were weaker than cast gels, undergoing delamination at the weak semi-fused sites between printed layers. Release tests were carried out and the 3DP were found to release more vitamin B1 compared to cast gels (78% vs 66% after 6 hours at 37 ˚C) owing to the layering allowing water to penetrate more quickly into the gel network.

Sunflower oil (SFO) was then added into the systems by creating oil-in-water emulsions and then dispersing the кC within them to produce emulsion gels. This gave a system with controllable energy content and the ability to encapsulate lipophilic molecules in a straightforward manner. Two emulsifiers were used, tween 20 (T20) and whey protein isolate (WPI). T20-stabilised emulsions underwent flocculation upon addition of the кC, but the WPI-stabilised emulsion gels did not. DSC showed that if the concentration of кC was fixed at 3% w/w in the aqueous phase, then addition of up to 40% w/w sunflower oil did not affect the gelling temperatures (36-37 ˚C). This was reflected in the printability not being affected by varying the oil phase from 0-40% w/w. Post-printing rheology and texture profile analysis found that increasing the oil fraction did not affect the tested mechanical characteristics of the 3D printed gels as they still failed along the semi-fused sites between layers.

Finally, to build on this work the emulsion gels were tested for stability and it was found that the oil droplet size remained constant over 8 weeks. Cinnamaldehyde, a lipophilic molecule was added to the oil phase and release tests were carried out. Unlike the vitamin B1 there was no significant difference in the final amount of cinnamaldehyde released over six hours between cast and 3D printed кC-emulsion gels. Lastly, erioglaucine disodium salt (EDS) was added and co-release was carried out. The EDS was found not to interfere with the release of the cinnamaldehyde and it released faster from the 3D printed gels compared to the cast gels.

Overall кC-gels were found to be suitable for 3D printing under a narrow range of parameters with and without sunflower oil. The 3D printed gels perform differently to cast gels in terms of mechanical properties owing to the presence of semi-fused sites running throughout them. They can be utilised as customisable release vehicles that release hydrophiles at a faster rate and lipophiles at a similar rate compared to the equivalent cast gels.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):