Comparative Evaluation of Maceration and Ultrasound-Assisted Extraction Methods on Phytochemical Profile, Total Phenolic and Flavonoid Contents, and Antioxidant Activity of Ethanolic Extracts from Selected Locally Available Philippine Citrus Fruit Peels

Citrus fruits are widely cultivated for their flavor, nutrition, and economic value. However, in the Philippines, limited research exists on local species like Citrus microcarpa, C. maxima, C. aurantium, and especially C. hystrix var. micrantha, particularly regarding peel utilization and extraction methods. This study evaluated the efficiency of maceration and ultrasound-assisted extraction (UAE), using absolute ethanol, in extracting bioactive compounds from these citrus peels. Extracts were screened for phytochemicals and evaluated for total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity via the DPPH radical scavenging assay. Percent yields were comparable between methods, with UAE achieving similar yields in significantly shorter time, indicating its extraction efficiency. Phytochemical analysis confirmed the presence of alkaloids, flavonoids, phenols, reducing sugars, saponins, tannins, and terpenoids across most samples. Among the species studied, C. microcarpa exhibited the highest TPC (62.66 ± 2.04 mg GAE/g via UAE) and TFC (83.85 ± 2.23 mg QE/g via maceration), correlating with the strongest antioxidant activity (lowest EC₅₀ values: 98.43 ± 0.79 μg/mL via maceration; 131.08 ± 1.77 μg/mL via UAE). Maceration was more effective for flavonoid extraction, while UAE enhanced phenolic yield, and antioxidant activity varied by species and method. Additionally, a significant positive correlation was found between TPC and TFC (r = +0.7833), with both showing strong negative correlations with antioxidant EC₅₀ (r = –0.9282 and r = –0.7324, respectively). These findings highlight citrus peels, especially from C. microcarpa, as promising antioxidant sources. The study recommends optimizing extraction conditions and conducting further bioactivity testing to assess therapeutic potential.