3D printability and biochemical analysis of revalorized orange peel waste

Abstract

Orange peels are often discarded as food waste despite being a nutritious source of vitamins and antioxidants. These orange peel wastes (OPW) are produced in millions of tons globally every year; discarding them results in detrimental environmental and economical impacts. This paper discusses the application of 3D printing technology to effectively upcycle the OPW into edible, healthy snacks for consumption. We aimed to develop a method to enable OPW to formulate 3D-printable inks for direct ink writing (DIW). Using DIW 3D printing, we successfully created edible constructs of rheologically modified inks containing OPW. The formulated ink possessed an initial viscosity of 22.5 kPa.s, a yield stress of 377 Pa, and a storage modulus of 44.24 kPa. To validate the method, we conducted a biochemical analysis of the OPW at each stage of the fabrication process. This study suggested that our ink formulation and 3D printing process did not affect the content of bioflavonoids and antioxidants of the OPW. The cell viability test using human dermal microvascular endothelium (HMEC-1) suggested that the OPW did not exhibit cytotoxicity throughout the entire process of the ink manipulation. Overall, this study has highlighted a potential scenario to revalorize food waste into the food value chain using 3D printing toward more sustainable and circular food manufacturing and consumption.

Viscoelastic properties of thermosensitive gelatin/tragacanth hydrogel as novel ink suitable for additive manufacturing: Effect of various additives on system's viscoelastic characteristics and printability

“…However, samples containing the rice starch and HNT are within the acceptable range. Comparatively, with regards to printability criteria, the GTAhr sample shows better stability during 60 min than the gelatin preheated and cross‐linked by transglutaminase enzyme 15 …”

“…Advances in extrusion‐based 3D printing over the past decade have made it possible to print intricate constructs from challenging natural biopolymers such as gelatin. A variety of strategies have been developed to improve the fidelity, resolution, and complexity of printed shapes 15 …”

“…Depending on the pH, the bloom strength, and the concentration, gelatin dissolves in aqueous solutions at a temperature between 30 and 37°C 17 . Because gelatin films have high hardness and fracturability 18 and breakdown at physiological temperatures, gelatin without additives has weak self‐supporting properties; that is, in the absence of crosslinking, its patterns degenerate inside the human body due to the physiology 15 . Gelatin films are reversibly dissolved in an aqueous environment.…”

“…Therefore, the formation of permanent bonds in the structure of gelatin would help to make it more stable. In order to maintain the integrity of the gelatin structure, the employed techniques to cross‐link gelatin include photocrosslinking (gelatin‐methacryloyl) 19 or photo cross‐linking through the addition of a photo initiator, 9 enzymatic (using transglutaminase), 15 and chemical cross‐linking. 20 Besides, other methods such as preheating gelatin 15 and using modifiers 20,21 help to improve the mechanical, rheological, and printability properties of gelatin‐based inks.…”

“…In order to maintain the integrity of the gelatin structure, the employed techniques to cross‐link gelatin include photocrosslinking (gelatin‐methacryloyl) 19 or photo cross‐linking through the addition of a photo initiator, 9 enzymatic (using transglutaminase), 15 and chemical cross‐linking. 20 Besides, other methods such as preheating gelatin 15 and using modifiers 20,21 help to improve the mechanical, rheological, and printability properties of gelatin‐based inks. In general, the methods that improve the duration of printing before nozzle clogging, controlling the temperature of the gelatin solution by heating the nozzle and the immediate reduction of solution temperature after exiting the nozzle ameliorate the printability properties.…”