Optimizing 3D printing and post-processing with sustainable bio-based inks: A comparative study on formulations...

Brewer's spent grain (BSG), a major by-product of the brewing industry, was utilized to produce brewer's spent grain protein (BSGP) and cellulose hydrolysate, the latter of which was subsequently used as a substrate for the fermentation of Rhodotorula glutinis to obtain Rhodotorula glutinis powder (RGP). By optimizing 3D printing ink formulations based on BSGP, RGP, and soy protein isolate (SPI), the rheological properties, 3D printing performance, and post-processing capabilities of the inks were investigated to develop a bio-based ink suitable for 3D printing with balanced nutritional composition and desirable bioactivity. Results of physicochemical characterization further elucidate the interaction mechanisms among the internal components of the inks. Compared to the control group, the addition of RGP reduced the storage modulus and apparent viscosity of Ink-A, which moderately improved the 3D printing performance but resulted in poor mechanical strength of the printed products. With the incremental addition of BSGP, the hydrogen bonding interactions within the composite inks containing BSGP, RGP, and SPI were strengthened, effectively limiting the free movement of internal water molecules. Consequently, the rheological properties of Ink-B, Ink-C, Ink-D, and Ink-E were significantly enhanced, leading to varying degrees of improvement in the 3D printing performance. Notably, Ink-D with a 30 % BSGP content exhibited balanced textural and rheological properties, enabling the production of 3D-printed products with high printing precision. Moreover, the printed products from Ink-D maintained excellent dimensional stability and strong antioxidant activity after steam heating treatment.