Green extraction of phenolic compounds from Red Radicchio of Treviso Precoce I.G.P. (Cichorium intybus L. var. Silvestre) by-products using Natural Deep Eutectic Solvents

Recovering polyphenols, a class of bioactive compounds known for their significant health-promoting effects, is crucial, especially from sources that are considered waste by the food industry. Additionally, there is growing interest in employing a green extraction approach. Within this context, this study aimed to select and optimize the most promising natural deep eutectic solvent (NaDES) for sustainable polyphenols extraction from red chicory of Treviso Precoce I.G.P. processing residues. Among four NaDESs tested for their ability to extract phenolic compounds, the citric acid: choline chloride (1:2) NaDES stood out as the most effective. To achieve maximum polyphenol yield, a three-factor, three-level Box-Behnken experimental design along with Response Surface Modeling (RSM) was used. The key factors for optimization were the acid: choline chloride molar ratio, the water percentage in NaDES, and the ultrasound extraction time. Total phenolic content, total flavonoid content, and total monomeric anthocyanin content together with the antioxidant activity and HPLC-DAD analyses were used to assess process efficiency. The experimental results revealed that the most favorable conditions for extraction were achieved using a citric acid: choline chloride molar ratio of 3:2, with 25% water content in NaDES, and an ultrasound extraction time of 49 minutes. This resulted in obtaining 117.43 ± 0.33 (μg/ml) of chlorogenic acid and 28.94 ± 0.22 (μg/ml) of chicoric acid. Considering NaDESs' green nature, biodegradability, and low cost, the obtained polyphenolic extracts are expected to be advantageous in industrial food and pharmaceutical applications, without demanding and expensive downstream purification steps.