Maximum valorization of red prickly pear peels through green extraction techniques of bioactive compounds and cellulose microfibers

This study evaluated the effect of particle size (375–116 μm) on the chemical composition of red prickly pear (Opuntia ficus-indica) peels, as well as on the ultrasound-assisted extraction of bioactive compounds using an ethanol:water (40,60 v/v) solvent at 30 °C. Residual biomass was used to obtain cellulose fiber (CF) suspensions via alkali hydrogen peroxide pretreatment and mechanical homogenization. Smallest particle (< 188 μm) significantly enhanced antioxidant activity (6.5 mg of gallic acid equivalents/g dw, IC₅₀, 0.7 mg/mL). X-ray diffraction confirmed reduced crystallinity of CF, with the highest crystallinity index (61 %) in particles 116 μm. Infrared spectroscopy identified the presence of phenolic, carboxylic acid, and betalain compounds in the extract and confirmed the removal of non-cellulosic components. Morphology analysis showed network of CF with diameters around 180 nm for the smallest particles. Thermal analysis indicated that the thermal decomposition of CF occurs at 350 °C, higher than raw peel (300 °C), confirming improved thermal stability.