Microwave-assisted extraction of phenolic compounds with antioxidant and anti-proliferative activities from supercritical CO₂ pre-extracted mango peel as valorization strategy

This work includes the second/sequential stage of a green-based valorization strategy of mango peel. An exhausted biomass from a pilot-scale CO₂ supercritical extraction process was reused for obtaining phenolic-rich extracts with high antioxidant and anti-proliferative activity, employing microwave-assisted extraction. The effects of microwave power (400–800 W), liquid-to-solid ratio (10–50 mL/g) and extraction time (60–120 s) on process yield, phenolic content, and antioxidant capacity were investigated using a Box-Behnken design. A solution consisting of 60% aqueous ethanol was used as extraction solvent. The results showed that microwave power and liquid-to-solid ratio were the most influential factors on the responses variables. The highest total phenolic content (52.08 mg gallic acid eq./g d. w.) and antioxidant activities (2.75 mmol trolox eq./g extract, and of 6.47 μg/mL expressed in DPPH, EC₅₀) were obtained at 800 W, 50 g/mL, and 90 s. Mango peel extract recovered at optimal conditions provided high anti-proliferative activity against HT-29 colon cancer cells line, after 24 h treatment (IC₅₀ = 22.98 μg/mL). Gallic acid derivatives, such as galloyl-esters, xanthones like mangiferin, flavonoids, including quercetin and quercetin glycosides were tentatively identified by ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry. Most probably, the compounds responsible for the outstanding anti-proliferative activity.