Optimization of ultrasounds assisted extraction of polysaccharides from cladodes of Opuntia ficus-indica using response surface methodology

In this work, polysaccharides are extracted from cladodes of Opuntia ficus-indica using Ultrasounds-Assisted Extraction (UAE). UAE operating conditions are optimized by a Face Centered Central Composite Response Surface Design (FCCRD) with four variables at three levels. The optimal operating conditions are obtained using Response Surface Methodology (RSM) and are the following: Solid-Liquid ratio SL = 1:10 w/v, pH = 2.5, time t = 20 min, and temperature T = 65 °C. The predicted extraction yield (12.07 ± 1.7 % dw) is in line with the experimental one (11.32 ± 0.25 % dw). The resulting extract is composed mainly of galacturonic acid (25.55 ± 0.30 %), the primary constituent of pectic material, followed by arabinose (14.34 ± 0.01 %) and galactose (13.5 ± 0.22 %). The Esterification Degree (ED) is found 42.84 ± 0.48 %, indicating the extract is Low-Methylated (LM). The FT-IR spectrum demonstrates that the extract has several peaks typical of polysaccharides. Total Phenolic Content (TPC) is equal to 41.33 ± 3.53 μgGAE/g (dw) and the anti-radical ability against the DPPH radical scavenging activity achieves 95.56 % at a concentration equal to 2 mg/mL, demonstrating that the extract is a polysaccharide functionalized with polyphenols. These results can encourage the use of the extract as a new ingredient in nutraceutical cosmetic applications.