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

xanthan gum. The formulated ink also maintained its hydrocolloids. We explored the use of extrusion-based
antioxidant properties before and after printing. Our study food printing as a method of food processing. In particular,
demonstrated a simple method to recycle and reduce food this work focused on characterizing (i) printability of the
waste toward food sustainability. inks arising from their rheological properties and (ii) key
biochemical properties at three critical stages of food
Citrus fruits, which are members the Rutaceas family, processing (i.e., ink preparation and extrusion printing).
are among the most widely consumed and grown fruits The usage of orange peels in 3D printable inks has
in the world, with a report indicating production to have previously been demonstrated as a nutritional supplement
exceeded 130 million tons in 2015 . Among the various additive, with the orange peel containing 0.8% of the
[2]
types of citrus fruits, the sweet orange (Citrus sinensis (L.) ink . In this work, we intend to demonstrate the use of
[30]
Osbeck) is a well-known source of natural antioxidants the OPW as the bulk printing material. We successfully
and certain phytochemicals (such as vitamin C and formulated OPW inks with 0.4%–1.0% xanthan gum. Our
bioflavonoids) crucial for supporting nutrition and well- rheological characterization suggested that the printable
being . According to projections for 2020/2021, orange OPW ink with 1.0% xanthan gum possessed a yield stress
[3]
production worldwide will rise to 49.4 million metric of 377 Pa and a storage modulus of 44 kPa. Using this ink,
tons. It is anticipated that the quantity of OPW will we characterized the biochemical properties of the OPW
increase concurrently with rising orange demand and at three critical stages during the fabrication: (i) powder,
consumption . OPW is often recycled as animal feed, (i) ink, and (iii) print. Our characterization suggested that
[4]
composted, or disposed of through incineration. To this the formulation of the ink and printing did not affect the
end, it is beneficial to develop alternative ways to upcycle content of bioflavonoids and antioxidants of the OPW.
OPW to revalorize them back to the food value chain. The cell viability test using human dermal microvascular
3D printing is a manufacturing technique which uses endothelium (HMEC-1) suggested that the OPW did not
layer-by-layer deposition to create items. It has been used exhibit cytotoxicity throughout the entire process of the ink
in numerous research areas, such as microfluidics [5-7] , manipulation. While this work used OPW as an example
metal printing [8-10] , and bioprinting [11-13] . In recent years, of an underutilized fruit waste, the principles and methods
food printing has been widely demonstrated with DIW discussed in this work should apply to other edible food
technology based on liquid extrusion. Customization waste for DIW 3D food printing.
of nutrients, creation of esthetically pleasing food, and
changes to the internal structure of food are all made 2. Materials and methods
possible through 3D food printing [14-16] . Edible constructs
with various internal structures provide distinctive textures 2.1. Nomenclature
during ingestion, which can be facilitated by the computer To distinguish the formulations between the inks, the
design of the 3D food model [17-19] . Thus, by modifying the samples were labeled as a percentage of OPW powder and
mechanical properties of the printed meal, 3D food printing a percentage of xanthan gum in the deionized water. For
may offer prospective health benefits . Chocolate , example, the ink containing 20% w/w of OPW mixed with
[20]
[21]
milk , mushroom , gelatin , and fish are just a few 0.4% w/w xanthan gum was labeled as O20XG4. Unless
[22]
[24]
[23]
[25]
examples of foods that have been used as ingredients in otherwise noted, this nomenclature was used throughout
3D food printing based on DIW. 3D food printing allows this paper.
designing the mechanical properties and esthetics of the
printed food, while it is crucial to ensure that the nutritional 2.2. Preparation of orange peel inks
contents of the food are not compromised. Recent research OPW and deionized water were used to formulate
has demonstrated that 3D food printing allows repurposing OPW inks. Fresh OPW was collected from a fruit juice
regularly discarded yet nutritious edible food byproducts vendor (Uglyfood, Singapore) as food waste. The OPW
like okara , potato peel , insect proteins , and grape was then dried in an oven heated at 60°C for 24 h. Dried
[26]
[28]
[27]
pomace , enabling us to utilize them in our daily diets. OPW was ground into OPW powder using a 2000-W
[29]
DIW 3D printing requires multiple steps to handle the food kitchen blender at 28000 rpm for 10 min. Next, the OPW
materials (e.g., ink formulation and extrusion). Despite the powder was sifted using a 300-mm sieve (Industrial and
potential benefits of this approach, the impact of DIW 3D Laboratory Consumables, China). OPW ink samples
printing on the biochemical properties of food waste has were prepared by adding OPW powder into deionized
not been studied carefully. water containing xanthan gum at different formulations
between 0.4% and 1.0% (e.g., O20XG4, O20XG6,
To bridge this gap, this work aimed to develop a O20XG8, and O20XG10). All food inks were mixed
method to create 3D structures using OPW mixed with thoroughly with a planetary centrifugal mixer (Thinky
Volume 9 Issue 5 (2023) 511 https://doi.org/10.18063/ijb.776