Page 525 - IJB-9-5

International Journal of Bioprinting 3D printability and biochemical analysis of orange peel waste

3.4. DIW printing inflammatory action, suggesting the potential to upcycle
The printability of the inks was tested by printing distinct the bioactive flavonoids from the orange peel, as a natural
lines of 20 mm; the consistency and the continuity of the product, to target cardiovascular health benefits .
[34]
ink was characterized (Figure 3A). With a constant printing Hence, many studies have evaluated numerous natural
speed and extrusion pressure, the ease of extrusion was products as potential treatment or prevention of chronic
observed with an increase in xanthan gum concentration diseases such as cardiovascular diseases [48-50] , diabetes [40,51] ,
(Figure 3B). The line width increased from 0.8 mm to hypertension [52,53] , and reproductive disorders [54,55] . While
2.8 mm for O20XG4 and O20XG10, respectively. The orange peel contains polyphenolic compounds, it remains
increasing line width indicated the increasing amount of unclear if 3D food printing affects the biochemical profile
material extruded, which is consistent with the Hagen– of the food product and the antioxidant activity. In this
Poiseuille equation. Practically, a low extrusion pressure study, we measured the levels of narirutin and antioxidant
during printing is experimentally preferred as each capacity and compared them among three crucial stages of
instrument has maximum pressure that can be handled. food printing (i.e., powder, ink, and print). The narirutin
This outcome is also in line with the measurement of the levels of orange peel powder were comparable among the
viscosity and the yield stress with respect to the xanthan three stages (Figure 4). Similarly, the antioxidant capacity
gum concentration. To analyze the printability of the of orange peel powder was evaluated using the DPPH
inks beyond the straight line, we printed two-layer grids and ABTS assays (Figure 4B and C). It was evident that
to identify the structural integrity of the printed strut in neither the formulation of food ink nor the 3D printing
the z-plane . The inks between O20XG4 and O20XG8 had a significant effect on the antioxidant capacity, which
[36]
exhibited various degrees of sagging within the overhang is characterized by their ability to scavenge free radicals.
region. However, the color map indicated that O20XG10 These experiments suggested that DIW printing did not
demonstrated a solid printed line across the overhang change the antioxidant capabilities of the OPW while
region, potentially applicable to creating 3D structures readily manipulating the physical properties and the
(Figure 3A). These results suggested that O20XG10 was the structures of the OPW. These experiments also indicated
most suitable formulation (among the inks we investigated) that adding xanthan gum did not compromise the
due to the formation of distinct and continuous lines at low antioxidant capabilities originating from the OPW.
pressure. We, therefore, used O20XG10 to print display 3.6. Cell culture and cell viability
pieces of 3D-printed OPWs (Figure 3C). Subsequently, Lastly, we evaluated the cytotoxicity of the OPW at the
O20XG10 was used to characterize their biochemical different stages of 3D food printing. We treated the cells with
properties at different steps during DIW 3D printing.
extracts from various 3D food processing stages for 24 h
3.5. Antioxidant capacity of OPW inks and observed the cell viability. The experiment suggested
The earlier results affirmed the capability to print no significant differences in cell viability, morphological
3D models of OPW. Thereafter, we characterized the changes and/or contamination after exposure of cells to
biochemical properties of OPW at each step of 3D printing: orange peel extracts from three different stages of food
(i) formation of the powder, (ii) formulation of the ink, and processing. DIW printing did not produce any potential
(iii) extrusion by DIW 3D printing. Orange peels are a rich cytotoxic substances detrimental to the cells (Figure 4D).
source of naturally occurring bioactive compounds such Overall, 3D printing of OPW did not compromise the
as flavonoids and other polyphenolic compounds [33,34,37-39] . chemical composition of the food and its biological activity
Previous studies have reported the abundance of two during the ink preparation and extrusion printing.
flavones (i.e., hesperidin and narirutin) in orange
peels [33,34,37-39] . Specifically, hesperidin (476.0 ± 8.6 mg/ 4. Conclusion
100 g of dry weight) and narirutin (241.3 ± 14.4 mg/ 100 g This paper presents the DIW 3D printing of OPW, which
of dry weight) were measured as the highest yields in consists of sieved orange peel wastes mixed with xanthan
earlier studies [34,37,38] . These compounds are well reported gum. We characterized the rheological properties of the inks
for their health benefits due to their potent antioxidant [40,41] with various concentrations of xanthan gum; we identified
and anti-inflammatory activities [42-44] . Cardiovascular O20XG10 as the most suitable for extrusion printing with an
diseases are one of the leading causes of death worldwide, initial viscosity of 22.5 kPa, a storage modulus of 44.25 kPa,
which are attributed to oxidative stress and chronic and a yield stress of 377 Pa. O20XG10 displayed the most
inflammation [45-47] . A recent study demonstrated that distinct and continuous printed lines during the extrusion
treatment of orange peel extract reversed TNFα-induced tests. LC/MS and cell viability analyses of the OPW powder
endothelial dysfunction in vitro primarily through anti- and ink suggested that the entire process did not compromise

Volume 9 Issue 5 (2023) 517 https://doi.org/10.18063/ijb.776