Ingredients, Nutritional Value and Food Safety

3D printing in the food industry is a digitially controlled, robotic construction process which can build up complex 3D food products layer by layer.

Ingredients for 3D Food printing

A wide range of food sources including insects, vegetables and animal by-products can be used for food printing. Ingredients can be classified into:

• Liquids: performed via extrusion or inkject processes
• Powders: printed by deposition followed by application of a heat source (laser or hot air) or a particle binder
• Cell cultures: deposition of cell cultures, also known as bioprinting, is a technique applied to print meat analogue

The food material used must be flowable during layer deposition whilst ensuring and maintaining high mechanical strength. The flowability can be achieved by ensuring that the food material is made of small-size particle but also by plasticization and melting. The self-supporting structure or high mechanical strength is achieved by the reverse process or by gelation. In order to ensure both flowable food material and a high mechanical strength in all of the layers, shear-thinning food inks is used.

Ingredients for food printing can be divided into three categories:

1. Natively printable materials

The natively printable materials can be directly extruded from a syringe (this is the case of dough, cheese, chocolate, icing, hummus, butter) or are in form of powder (sugar, starch, etc). Generally, they can be extruded without the addition of flow enhancers and, after deposition, they are able to support their own structure.

2. Non-printable traditional food materials

Flow and viscosity enhancers must be added to the non-printable traditional food materials, which include meat, rice, vegetables and fruits, in order to make them suitable for the extrusion process. Substances commonly used include starch, pectin, gelatin, xanthan gum, agar, and alginate.

3. Alternative ingredients

Alternative ingredients include novel sources of functional and bioactive compounds such as proteins and fibres isolated from insects, algae, microorganisms, and residues from agricultural and food processes.

3D printing is also effective in the exploitation of agri-food residues. For example, ground potato by-products (a food material having a high fibre content) can be mixed with yam powder and hot water to obtain a printable paste usable to produce air-fried snacks.

3D printers can also print foods that doesn’t exist in nature. This is the case of the concept food called “edible growth” that is a self-contained, multi-ingredient food enriched with living edible plants and fungi that grow from them. This food should be produced by Fused Deposition Modelling applied to an edible matrix made of dried vegetables/fruits, nuts, or Agar Agar. Successively, seeds of edible plants, spores of fungi, and yeast and bacterial cells are added to this nourishing matrix and covered with and edible film made of proteins or carbohydrates. Seeds and fungi use the matrix as a growing substrate. Within few days, plants and mushrooms grow up and the snack is ready to be eaten.

Nutritional Characteristics

3D food printing technologies can be used for the production of a large variety of ready-to-eat foods suitable to satisfy the demand of both people with specific food-related diseases (for example, celiac disease, diabetes, hypertension, obesity); people with personal nutritional habits (vegetarian, vegan, etc.); or other needs (e.g. with swallowing and chewing difficulties).

The literature illustrates some examples of the application of 3D printing to produce nutritive/healthy foods. For example Derossi et al. produced a customised fruit-based snack to supply the 5–10% of energy, calcium, iron, and vitamin D required by children of 3–10 years old. However, to date, most applications of 3D food printing have been developed to test the complex structures of the food, without consideration of nutritional value.

Food Safety

The safety of 3D printed food is complex. This is because of the contact between the parts of 3D printers and the food ingredients/food under production with microbiological hazards of a concern, as well as the migration of leachable substances.

Before extrusion, most of the food materials need to be heated in order to create a malleable paste suitable to pass through the extrusion nozzle; and, after printing, the food structure needs to be cooled in order to increase its mechanical strength. Heating and cooling operations might make food more susceptible to microbial growth. Thus, effective cleaning protocols and sanitization of 3D printers before printing food is important. Similarly, the parts of the 3D printer that come into contact with foods must be: safe under normal use conditions, durable, corrosion-resistant, non-absorbent, and accessible to inspection; have easily cleanable surfaces; have no breaks and sharp internal angles.

The 3D printers specifically built for food use meet all these requirements but, sometimes, are very expensive. Instead, the 3D printers that have additional food printing functions are relatively cheap but many of their components are made of plastic materials, which may release ultra-fine toxic particles during the printing process and lead to adverse health effects. In order to reduce the risk of particle migration and bacteria growth, it is advisable to coat the 3D printed parts with food grade epoxy or polyurethane resins to seal their surfaces.

To date, there is a low number of scientific articles investigating the safety of 3D food printing. Thus, more research in this area is required.