HYDROGELS BASED ON QUINOA STARCH RECOVERED FROM BY-PRODUCTS: EFFECT OF CITRIC ACID AND TARA GUM ON PRINTABILITY QUALITY FOR 3D PRINTING APPLICATIONS

Hydrogels based on starch are more commonly used in 3D printing to fabricate sustainable, biocompatible structures, primarily in food engineering, biomedicine, and agriculture. The study aimed to evaluate hydrogels based on quinoa starch isolated under conventional wet (C-QS) and ultrasound-assisted (US-QS) conditions. These starches were blended with tara gum (TG) and citric acid (CA). On the one hand, TG (1%) and CA (1.2%) were dispersed in distilled water under magnetic stirring (500 rpm) at 40 °C and 50 °C, respectively. On the other hand, starch dispersions of C-QS and US-QS were mixed with TG solution (500 rpm, 45 min, room temperature) and then heated at 81 °C to gelatinize for 20 min. Then, the pastes were cooled to 50 °C, and the CA solution was added with constant stirring (450 rpm, 10 min). Nine formulations of hydrogels were prepared for each starch C-QS (T1C–T9C) and US-QS (T1US–T9US) with its corresponding starch (6.76, 7.20, 8.04, 10.09, 10.49, 11.28, 12.05, 12.43, 13.18%, w/w) in blends with TG (0.05, 0.253, 0.35%, w/w) and CA (0.05, 0.07, 0.12%, w/w). The dynamic mechanical spectra of all hydrogels were typical for a biopolymer gel network with a predominance of elastic over viscous character (G’>G’’, tan δ<1). The G’ values, at 1 Hz, of T1C-T9C and T1US-T9US hydrogels, ranged from 154.3 Pa to 3445.5 Pa, and from 169.3 Pa to 3795.5 Pa, respectively. All hydrogels exhibited pseudoplastic behavior (n < 1). The viscosity values, at 1 1/s, of T1C-T9C and T1US-T9US hydrogels, ranged from 15.0 Pa·s to 276.4 Pa·s, and from 14.4 Pa·s to 404.9 Pa·s, respectively. Experimental parameters were best fitted to the Herschel–Bulkley model. The t₀ values of C-QS hydrogels (9.68–203.47 Pa) were similar to those of US-QS ones (9.89–209.20 Pa); meanwhile, consistency index (k) values of C-QS (6.79–140.12 Pa·sⁿ) were slightly lower than those of US-QS ones (7.73–281.52 Pa·sⁿ). Hydrogel formulations for 3D printability were selected based on parameters proposed in the literature: G′>2000 Pa; 0.1<tanδ<0.22; 80<σ₀<120 Pa; 0.25<n<0.45; thus, the selected formulations for a further 3D-printing were T6C, T7C, T8C, T8US, and T9C.