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Lee, et al.
electronic devices , and fluidic devices [12,13] . DIW neurological development especially in infancy and early
[11]
3D food printing is an emerging field [14,15] , which childhood as it provides medium for absorption of fat-
allows customization of nutrients based on individual soluble vitamins A, D, E, and K .
[32]
needs , fabrication of aesthetically pleasing food , To bridge the gap, we demonstrated the extrusion of
[17]
[16]
and customization of food texture . Extrusion-based oil-based food ink through simple alteration of rheological
[4]
methods, such as hot-melt and cold extrusion, have properties with different concentrations of water and
been widely used in food printing because of their oil (Supplementary Figure 1). We first conducted oil
flexibility to dispense liquid-based food materials [18-20] . separation tests by varying the concentration of water
However, hot-melt extrusion is not always suitable to and additional coconut oil to determine the limits of the
print temperature-sensitive food because they require amount of oil present in the inks; the stability of the ink
an elevated temperature to melt food materials. As such, was crucial to ensure the smooth extrusion of material
there are increasing interests in 3D-printed, temperature- and the maintenance of the printed structures. Three
sensitive food materials through cold extrusion that relies inks with different water and oil contents were selected
solely on the rheology of ink [21,22] . Several foods such to characterize the rheological properties; the viscosity,
as chocolate-based ink , milk-based ink , vegetable- yield stress, and storage modulus of the ink are important
[22]
[23]
based ink , and gelatin have been used to demonstrate parameters for DIW to determine the printability and
[5]
[24]
3D food printing. For example, the addition of xanthan structure integrity of the printed models [22,23] . Mesh
gum and κ-carrageenan gum has been demonstrated structures were printed with all three inks to observe
to make mashed potatoes to form self-supporting the spreading of inks to determine printability. We also
structures adequate to maintain 3D structures . Printable performed texture profile analysis (TPA) for the printed
[1]
chocolate inks were achieved by altering the rheological mesh structures using inks with varying contents to assess
properties of chocolate ink by varying the cocoa powder the capability to achieve desired textural properties.
and chocolate syrup . These demonstrations have Extending the demonstration, we printed various 3D
[22]
highlighted the importance of the rheology of the food structures with suitable ink that did not exhibit oil
ink to achieve extrusion-based 3D printing. separation and spreading of ink. The knowledge we
Foods commonly comprise multiple constituents developed here should be useful to fabricate other food
such as carbohydrates, proteins, fats, small molecules, structures with high oil content such as sesame paste
[33]
[34]
and water. The interactions among different food and peanut butter , which should find a broad field of
constituents would affect the rheological properties and applications in the healthcare and food industries.
stability of inks . The protein in the food is known to be
[25]
amphiphilic that holds the hydrophobic and hydrophilic 2. Materials and methods
aggregates in the food matrix, and acts as an emulsifier 2.1. Preparation of coconut cream ink
that reduces the surface tension between two immiscible
materials such as oil and water. The presence of an The base material used was commercially available
emulsifier hence permits different constituents to mix . coconut cream powder (Kara Coconut Cream Powder,
[26]
Starch is a polysaccharide carbohydrate consisting of PT Pulau Sambu, Riau, Indonesia) that contained coconut
multiple glucose units joined together by glycosidic extract, hydrolyzed starch, and milk protein. Other
bonds , which can form entanglements networks to food materials used were coconut oil (Benefit Coco,
[27]
control the rheology of the food . The stability of the Singapore) and pandan extract (Bake King, Singapore).
[28]
ink, where no oil separation occurs, is crucial to prevent The samples were first prepared by adding coconut cream
rancidity, degradation of vitamins, and formation of powder into deionized water, with 0.2% w/w pandan
potentially harmful compounds . Moreover, the extract for color and flavor enhancement, at different
[29]
printability of ink would be affected due to the change in weight concentrations. Samples were then mixed
phase which would alter the rheological properties of the thoroughly for 5 min at 2000 revolutions per minute
ink. Hence, the control of the interactions among protein, (rpm) with a planetary centrifugal mixer (Thinky ARE-
carbohydrate, and oil is important to control the stability 250, Thinky Corporation, Tokyo, Japan), at 25°C (room
of the edible colloidal system . Despite the increasing temperature). Finally, coconut oil was added at different
[30]
interest in 3D food printing, there are limited works weight concentrations (5–30% w/w). The mixture was
on the effect of oil content on the printability of food homogenized again using a planetary centrifugal mixer
inks to date. 3D printing of food with high oil content for 5 min at 2000 rpm.
is challenging due to the occurrence of oil separation 2.2. Characterization of oil separation
and poor rheological properties. The addition of oils is
particularly crucial in providing energy and improving The oil separated from the ink was collected by filtering
the palatability of food . Moreover, it is important in the ink with a sieve immediately on preparation of the
[31]
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