Optimization of Ultrasound-assisted Extraction of Bioactive Compounds from Satsuma Mandarin Pulp Agro-industrial Residue Using Water and Water/ethanol Solvent Mixtures

Satsuma mandarins (Citrus unshiu Marc.) are widely consumed due to their taste and easy-to-peel thin skin. While primarily eaten fresh, market saturation has increased juice production, generating significant pulp residues, which remain rich in bioactive compounds and antioxidants like phenolic acids, flavonoids and carotenoids, making it a valuable resource for the food and pharmaceutical industries. Efficient extraction of these compounds, however, remains challenging. Ultrasound-assisted extraction (UAE) is an emerging highly efficient extraction technology that enhances bioactive compound recovery while reducing energy input and solvent use. This study optimized the UAE of bioactive compounds from mandarin pulp using either water or water/ethanol mixtures as green solvents. A Box-Behnken design within Response Surface Methodology was applied to assess the effect of three factors: a) solvent composition (water, 30% (v/v) ethanol and 60% (v/v) ethanol), b) treatment time (1, 8 and 15 min), and ultrasound amplitude (25, 50 and 75%). The analyzed responses were total polyphenolic content (TPC), total flavonoid content (TFC) and total carotenoid content (TCC). Results indicate that higher ethanol concentration, longer extraction time, and increased amplitude enhanced TPC and TFC extraction. In contrast, a lower ethanol concentration was optimal for TCC. Optimal conditions of 31% ethanol, 12 min extraction time, and 65% amplitude maximized bioactive yields. Validation experiments confirmed the model’s high predictive accuracy.