Efficient recovery of phenolic compounds from citrus processing by-products requires optimized solvent systems and reliable frameworks for comparing emerging extraction technologies. In this study, a solvent system was first optimized to maximize phenolic recovery from lemon (Citrus limon (L.) Burm. f.) processing by-products, enabling a standardized comparison of ultrasound-assisted extraction (UAE) and hydrodynamic cavitation (HC). A preliminary solid–liquid extraction screening using different water:ethanol ratios (v/v) identified a 50:50 hydroalcoholic mixture as the optimal solvent system for recovering phenolic compounds. HPLC analysis confirmed the presence of major flavanones (eriocitrin and hesperidin) and hydroxycinnamic acids (caffeic, p-coumaric, sinapic, and ferulic acids). Antioxidant capacity was assessed using complementary assays (Folin–Ciocalteu, DPPH, and ORAC) to provide a comprehensive evaluation of antioxidant activity. Under optimized solvent conditions, UAE significantly improved the recovery of total flavanones (+25.9%), hydroxycinnamic acids (+10.3%), total polyphenols (+20.5%), DPPH activity (+6.0%), and ORAC values (+9.6%) compared with conventional extraction. HC further enhanced extraction performance, increasing flavanone recovery by 12.0%, hydroxycinnamic acids by 7.2%, total polyphenols by 5.2%, and antioxidant activity (DPPH and ORAC) by 11.4% and 2.0%, respectively, relative to UAE. Following ethanol removal and concentration, HC-derived extracts showed the highest phenolic content and antioxidant capacity. These results demonstrate that solvent optimization, combined with a standardized comparison of extraction technologies, enhances phenolic recovery from lemon processing by-products. The findings indicate that HC is a promising, scalable approach for the sustainable recovery of bioactive compounds from citrus side-streams. The novelty of this work lies in the integration of solvent optimization with a systematic and standardized comparison of UAE and HC, providing a reproducible framework for evaluating emerging extraction technologies and highlighting the enhanced performance and scalability potential of HC for phenolic recovery from citrus processing by-products.
Ballistreri et al. (Sat,) studied this question.