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3D Printing of Food Foams
into larger bubbles, which stabilize the foams. However, XG (Figure 1D), and the difference was statistically
the increase in density also makes it harder for the foams significant. The spreading was caused by both foam
to form, resulting in a lower overrun. instability and lack of ability to retain water. XG thickened
the foams by increasing the viscosity of the liquid phase
(3) Foam density and forming a hydrogel phase . This prevented water
[31]
The EW foams (Inks 1 and 2) are generally denser than from spreading on the filter paper, greatly reducing
the HPMC foams. The HPMC forms a light foam as a water spreading of Inks 2, 4, and 5. Without XG, while
result of the large overrun. The XG increases the density Ink 1 had the protein films to hold the air bubbles and
as shown in Figure 1C, where there is a slight increase in water migrated to the filter paper due to strong capillary
density from Ink 1 to Ink 2 and from Ink 3 to Ink 4. The force. Likewise, for Ink 3, water between the air bubbles
density affects the foaming ability inversely; as discussed migrated from the food ink to the filter paper. Over time,
previously, the overrun is lower when the density is the area of wetting increased when the foam collapsed.
higher. Ink 5 has a higher density than Ink 3 and 4 as it For Inks 4 and 5, XG prevented the water from leaking
contains more HPMC, thus making it more difficult to be onto the filter paper. Over time, water evaporated, thus
aerated and leading to a denser foam. resulting in a slight shrinkage of the area of the foam.
(4) Water retention 3.3. Rheological properties of the inks

Syneresis refers to the undesired leakage of water from All the five inks displayed a shear-thinning or
food. This study investigates the ability of the foam ink to pseudoplastic property (Figure 2A). Shear-thinning
retain water. In the case of foams, the spreading of water properties were preferred for extrusion printing as they
affects the integrity of the printed structures, causing suggested that the food ink could be easily extruded
the print to spread and collapse due to instability. In this and held its shape after extrusion. The printability and
study, the amount of water leakage from the foam inks self-supporting structure depended on the viscosity and
[33]
was obtained by measuring the area wetted on a piece of yield stress, respectively . The low viscosity of the
filter paper. inks allowed them to be printed easily through extrusion.
Inks that do not have XG (Inks 1 and 3) had a large When the shear rate increased, the viscosity of the ink
amount of spreading compared to the inks containing decreased, allowing the ink to flow out smoothly. The EW

A B

C D

Figure 1. Foam properties (A). The foaming ability of each foam ink based on their overrun. (B) The foam stability of each foam ink.
(C) The density of each foam ink. (D) The syneresis results of each ink. *P ≤ 0.1, **P ≤ 0.01, ***P ≤ 0.001, ****P ≤ 0.0001 for the t-test
results (n=3).

160 International Journal of Bioprinting (2021)–Volume 7, Issue 4