Recovery of polyphenols from corn cob (Zea mays L.): Optimization of different green extraction methods and efficiency comparison

The present work focuses on the recovery of polyphenols from Lombard corn cob to develop a new upcycled ingredient. Three different green extraction methods were evaluated using an experimental design approach: a conventional extraction (CSE-HA) and a microwave-assisted extraction (MAE-HA) using hydroalcoholic solvents, and a more innovative MAE method using natural eutectic solvents (MAE-NaDES). From mathematical modelling, three optimized extracts were obtained: CBE-1 from CSE-HA (50.3 % of ethanol, 60 degrees C, 89.9 min, and 32.7 mL/g solvent solid ratio - SSR), CBE-2 fom MAE-HA (62.4 % ethanol, 88 degrees C, 5 min, and 42.8 mL/g SSR), and CBE3 from MAE-NaDES (20 % water content, 90 degrees C, 5 min, and 20 mL/g SSR). The highest polyphenolic yield, reported as total metabolites content (TMC), was obtained for CBE-2 (TMC=285345.0 +/- 3737.67 milli Absorbance unit per second -mAu*s), followed by CBE-1 (TMC=242965.2 +/- 3411,5 mAu*s) and CBE-3 (TMC=108000.2 +/- 4530.03 mAu*s). Despite NaDES still appeared as promising solvents, the hydroalcoholic mixtures gave the best recoveries; at the same time, innovative MAE showed to be a sustainable approach, providing high yield within few minutes.