INULIN GRAFTED TO GALLIC ACID USING EFFICIENT AND GREEN DUAL INTERMEDIATE FREQUENCY ULTRASOUND PROCESS

The covalent conjugation of inulin (INUL) with phenolic compounds through chemical and enzymatic procedures represents a strategy to impart antioxidant capacity and enhance the prebiotic activity of INUL. However, the efficiency of these procedures needs to be improved. INUL from chicory with an average polymerization degree ≥ 10 and commercial gallic acid (GA) were used. The chemical dosimetry (OH° and H₂O₂) of the multifrequency ultrasound system (Meinhardt Ultrasonic, Germany) was determined by the potassium iodide method and modified Weissler. INUL-AG was obtained by the free radical H₂O₂ and ascorbic acid (Aa) procedure assisted by intermediate-frequency dual ultrasound (USDFI) in a one-pot approach. The aqueous INUL solution (5 mg/mL) was sonicated at 582 KHz, amplitude = 90 % for 10 minutes. Thereafter, Aa and exogenous H₂O₂ (molar ratio = 3.4) and GA (INUL/GA ratio = w/w) were added, and the mixture was sonicated at 1144 kHz, amplitude = 30 % for 20 minutes. As control, INUL-GA was conjugated by the conventional method in a 24 h reaction (MC). Aqueous solutions of INUL-GA were dialyzed on a membrane with a 3.5 kDa cut-off. The INUL-GA samples were characterized using the following methods: i) UV-Vis spectroscopy was performed in the range of 200-400 nm, and Fourier-transform infrared (FT-IR) spectroscopy was carried out in the range of 4000-400 cm-1 (resolution = 4 cm-1 and 32 scans) using a Genesys 150 (Thermo Scientific, USA) and a Spectrum Two (Perkin Elmer, USA) spectrophotometer, respectively. ii) The total phenolic compound content was determined using a rapid Folin-Ciocalteu method and iii) The antioxidant capacity was measured by the DPPH (2,2-diphenyl-1-picrylhydrazyl) assay. The results demonstrated that the USDFI-assisted procedure allows for the efficient production of INUL-GA in 20 min, which represents a reduction of more than 99% in the reaction time compared to the MC.