Page 52 - FoodFocusThailand No.231 June 2025

SMART PRODUCTION

3. Development of food printing inks
One of the key factors determining the success of 4D
food printing is the printability of the food material. Printability
is influenced not only by the material’s flow behavior through
the printer’s nozzle but also by its post-printing stability, which
is essential for maintaining the shape and texture of the
printed product. Three critical rheological properties of food
printing inks must be considered: (1) viscosity and shear-
thinning behavior, which allow the material to flow smoothly
through the nozzle; (2) yield stress and viscoelastic
modulus, which enable the printed structure to support its
own weight and retain its form; and (3) thixotropy, which
ensures that the material quickly recovers its structure after
the shear force applied during printing. Adjusting the ink
Figure 1 Color changes in printed food samples over time after composition helps maintain the microstructure, rheological
being sprayed with solutions of varying pH levels. properties, and overall printability. For example, incorporating
Source: Su et al. (2025) food additives such as dietary fibers or hydrocolloids
enhances viscosity, resulting in a more defined and
3. Natural pigments: Colorants such as anthocyanins, structurally stable printed product.
curcumin, and betalains are naturally found in fruits and 4. Post-processing control
vegetables, which can change color in response to variations Post-processing plays a critical role in enabling desired
in pH. transformations in the shape, color, or texture of 4D printed
4. Flavor compounds: Flavor compounds are typically foods. While certain products may undergo spontaneous
volatile and heat-sensitive, so they change over time. To control structural changes over time, key transformations often
their release, these compounds are often encapsulated and require external stimuli facilitated by appropriate post-
triggered by specific conditions, which are used to design during processing techniques. These methods include thermal
preparation or consumption. treatments (such as baking, frying, microwave heating,
infrared, or hot air), pH modification, moisture control, and
Forming Techniques by the 4D Food Printing light exposure (UV light). Microwave heating is particularly
Process effective due to its ability to induce rapid water evaporation
The formation of the printed structure in the 4D food printing and expansion, leading to visible shape alterations. In
process can be effectively controlled by adjusting four key contrast, chemical or acid-based pH adjustments, such as
factors as follows: spraying or immersing the printed product in a solution, can
1. Optimization of printing parameters effectively trigger color changes in food.
Most 4D food printing processes still rely on 3D food printers 4D food printing technology is currently being applied in
to create the initial structures. Common printing techniques the development of specialized foods for the elderly,
include extrusion-based printing, inkjet printing, which is suitable particularly those with dysphagia. The food formulation
for low-viscosity materials and simple structures, binder jetting, contains pea protein combined with purple sweet potato
which is ideal for creating more complex geometries with a starch as the main ingredients. These components are
firmer texture, and selective laser sintering. Among these, shaped using extrusion-based printing, a technique that
extrusion-based printing is the most widely adopted technique. enables customized soft textures while preserving essential
However, the extrusion process, particularly under shear stress, nutritional value. One of the key features of this application
significantly affects the microstructure of food materials. is the presence of anthocyanin pigments in purple sweet
Therefore, precise control during printing is essential to maintain potatoes, which exhibit environmentally responsive color
structural stability and functionality. Key parameters influencing changes (Figure 1), particularly in response to variations in
print quality include: (1) extrusion rate: Determines the flow pH levels. This characteristic enhances the visual appeal of
speed of the food ink. A consistent and optimized rate allows the food, making it more attractive for consumption.
for smooth and high structures. (2) nozzle diameter: Larger An optimal formulation of the food ink includes 17% purple
nozzles are better suited for highly viscous inks, such as those sweet potato powder, 4% pea protein, and 0.2% hydroxypropyl
made from concentrated proteins or starches, allowing for methylcellulose (HPMC). This composition provides excellent
continuous flow during printing. (3) infill pattern: The pattern is printability and produces food with desirable textural
related to the internal arrangement pattern of the printed properties, including appropriate hardness, cohesiveness,
material, which influences post-processing. stickiness, and elasticity—qualities suitable for individuals
2. Application of simulation software with swallowing difficulties. Moreover, the pH-sensitive color
The use of simulation software and numerical technologies transitions of anthocyanins offer visually dynamic and
plays a vital role in optimizing the 4D food printing process. customizable color changes, which not only enhance the
These tools help minimize trial-and-error steps by providing appearance of the food but also make eating experience
accurate predictions and guidance for process improvement. more enjoyable.
It simulates shape transformations before actual printing,
reducing material waste and improving overall efficiency.
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