Do you remember when we first mentioned 3D food printing (and our podcast episode)? I remember writing that this is a very innovative food processing technique. This indeed will have its use in foods and material sciences, medicine, and the pharmaceutical field (among the many).
If you read the article or listened to the podcast episode, you remember that we mentioned some particular challenges related to the printing material. It is funny because whenever I think about printing something, I think about colours, and I have this obsession with science and art. I see lots of colours in foods, and I believe that working with food is very similar to being an artist. That is above all a creative process, don’t you agree?
Printing material for 3D food printing
What are the ‘colours’ we can use if we want to produce, say, a 3D printed pizza or some 3D printed macarons? Of course, if you know how a 3D food printer works, you might be aware that the nozzle’s diameter and deposition speed have a significant importance in helping the material support its final shape. However, 3D printed foods and printable ingredients need to have two essential things to hold the shape of the finished product, and those two things are viscosity and mechanical strength.
We can use many ingredients (and most of us have them on our cupboards, nothing too exotic here) to produce 3D printed foods, and those are proteins, starches, and fats. We might benefit from the use of hydrogels too.
Proteins and 3D food printing
Proteins are large biomolecules, and they are made by chains of aminoacids. When a protein is under stress, such as mechanical stress or heating conditions, it denatures (nothing too bad actually, this is extremely useful when using proteins to make gels or emulsions). This means that a protein that usually has a globular shape starts to unfold just like a ball of wool. Proteins can then interact with one another and form a net, something similar to what happens when we play Twister. Proteins interacting with one another will help increase the viscosity and hold water, thus improving the printability of the solution (or matrix, as food scientists like to say) they are found in.
Starch and 3D food printing
Starch is the most common carbohydrate in our diets. It is made by the polymerisation of glucose molecules and is insoluble in water at room temperature but acquires an extraordinary functionality when treated at temperatures above 50C. When we put starch in water at a determined temperature (75-80C, very close to our cooking temperatures), the starch will start to swell by absorbing water, and by doing so, it will form a viscous paste. This phenomenon is generally recognised as starch gelatinisation.
This paste has a shear thinning property which means that the viscosity of the solution decreases under shearing, which is optimal if we think about 3D printing. The material behaves perfectly during deposition since the starch will easily squeeze out of the nozzle and hold its shape upon deposition.
Fats and 3D food printing
Fat is a macromolecular substance made by a large number of carbon atoms. They are generally divided into unsaturated and saturated according to the presence (or not) of carbon-carbon double bonds (C=C). Saturated fats are usually solid at room temperature and start to melt around 28-45C according to the type of fat. This sets good conditions for deposition and shape-holding during cooling since these fats can form self-supporting layers, which is optimal when 3D printing chocolate. However, in the case of chocolate, time, temperature, and speed of printing are extremely important as the material will quickly solidify upon deposition.
Hydrogels and 3D food printing
Hydrogels are polymeric networks that do not dissolve in water due to their chemically or physically cross-linked structure. These are prepared from macromolecules like carrageenan or xanthan gum. Hydrogels can produce a 3D structure that swells in water and can maintain volume without dissolving. This is why it looks so good in the eye of people designing 3D foods. A carrageenan hydrogel can be extruded and produce complex shapes hence used as an efficient ‘ink’ for food printing.
Non-easy to print materials
Not all materials are easy to print, and some of them are pretty tricky to use because they lack plasticity or are not viscous enough for deposition. Some ingredients like raw vegetables and fruit, when pureed, can undergo oxidation or browning, and this is something that is not advisable neither from the chemical stability point of view and from the consumer’s acceptance view too.
A good strategy that helps overcome materials’ printability issues is the use of a combination of ingredients to help increase the plasticity of the printable food and its shape retention ability.
Derossi and co-workers in 2018 designed a 3D printed food for children with a combination of pureed bananas, lemon juice, and other fruits rich in vitamins and pectin. It turned out to be an excellent strategy to improve the material’s printability and produce nutrient-rich foods.
Hands up if this article made you want to purchase a 3D printer for foods. I have the strange feeling that we will have a 3D food printer right next to our microwave oven in a few years. What do you think about it?
Are printable materials the next thing we will find on a supermarket shelf?
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