Spontaneous Color Change of 3D Printed Healthy Food Product over Time after Printing as a Novel Application for 4D Food Printing

A four-dimensional healthy food product was fabricated, in which 3D printed anthocyanin-potato starch (PS) gel changed its color over time to an attractive color (the 4th dimension). The color changed not only when sprayed the 3D product with different pH solutions but also independently as a response to an internal pH stimulus from another part inside the printed multi-material product. To achieve this, two parts of the gel system were combined, one part was from anthocyanin-PS gel and another part from lemon juice gel. In addition, the color change of anthocyanin-PS gel was also assessed after spraying with different pH solutions at different concentrations of PS and anthocyanin. Color changes were evaluated in terms of lightness (L*), redness (a*), and blueness (b*) using a colorimeter. The color stability of the 4D food product was examined for 24 h after printing. Moreover, a sensory evaluation test was performed to assess the consumer acceptance of the 4D food product. The printed samples sprayed with pH solutions 2, 2.5, 3, and 3.5 showed significant differences (p <= 0.05) in color at all PS and anthocyanin concentrations. However, pH samples 4, 4.5, and 5 did not show any visible difference in color after treatment compared to control samples. Furthermore, the color of the 3D printed anthocyanin-PS gel in model (A) gradually changed from purple to red over time during and after the printing process. On the contrary, the 3D printed anthocyanin-PS gel in model (B) did not show any noticeable color change over time after printing. This paper presents a novel application for 4D printing in the food field, which is very important for the food industry to fabricate a healthy product with attractive colors.