Formulation and characterization of functional gel ink based on skipjack tuna hydrolysate: Formula optimization, 3D printability, and antioxidation

To enhance the printability and function of 3D printed gel products, skipjack tuna hydrolysate (STH) with anti-oxidation was incorporated into the carrageenan-gelatin-hydroxypropyl methylcellulose (CGH) mixed system, as well as its printability and function were investigated. Results showed that the CGH mixed systemwith 10.50% carrageenan (C), 11.50% gelatin (G), 12.00% hydroxypropyl methylcellulose (H) had the best printing effects. Based on the optimized gel ink, 0.4% STH could further increase the gel strength, springiness, water holding capacity and G′ of 3D printed CGH gel by 38.27%, 124.74%, 13.13%, 36.76%, respectively, leading to the enhancement of supporting capacity, which could improve the 3D printing effects. These might be due to that 0.4% STH rised disulfide bonds (5.40%) and hydrogen bonds (73.44%), as well as decreased random coil content (3.92%) of protein, leading to the increased compactness and orderliness of the CGH gel network to improve the structure stability, which facilitated the printing process. Moreover, the 3D printed CGH gel containing 0.4% STH exhibited good anti-oxidation with the ABTS, DPPH, OH scavenging rates and total reducing power of 74.93%, 87.65%, 58.65% and 0.78, respectively. Thus, incorporating STH into the CGH not only improved printing properties but also enhanced antioxidant performance, which was favorable for the development of 3D-printed functional gel products.