Comparative Evaluation of Microwave- and Ultrasound-Assisted Extraction of Antioxidants from Parsley (Petroselinum crispum (Mill.) Fuss) and Coriander (Coriandrum sativum L.) Processing By-Products

Aromatic-herb processing generates large volumes of residues that remain rich in bioactive compounds yet are seldom valorised. This study compared the recovery of phenolic compounds and antioxidant capacity from parsley and coriander processing by-products under a fully crossed design combining two extraction methods (microwave-assisted; ultrasound-assisted), two temperatures (60 and 80 °C), two times (15 and 30 min) and three solvents (water, 50% ethanol, and 80% ethanol (v/v)). For each condition, four separate extractions were performed and combined into a single pooled extract, which was analysed in triplicate; the reported values therefore reflect analytical repeatability, and the between-condition comparisons should be interpreted accordingly. Each of the 24 conditions per species was characterised by total phenolic content (TPC), DPPH, and ABTS. Solvent composition was the dominant factor for both matrices, but in opposite directions of polarity: coriander TPC peaked in water (up to 49.71 ± 0.73 mg GAE/g DW), whereas parsley TPC peaked in 80% ethanol (7.18 ± 0.29 mg GAE/g DW), consistent with differences in the polarity of the extractable constituents. The conditions maximising TPC did not coincide with those maximising radical-scavenging activity, and DPPH and ABTS provided complementary rather than redundant information. In practical terms, coriander residues yielded the highest phenolic content with water, whereas their strongest antioxidant capacity (ABTS) was obtained with 50% ethanol under ultrasound; parsley residues required 80% ethanol with ultrasound. The best-performing condition therefore depended on whether phenolic recovery or antioxidant capacity was the target. These findings demonstrate that botanically related species require distinct, matrix-specific extraction strategies and support the tailored valorisation of aromatic-herb residues within a circular-bioeconomy framework.