Effect of Ultrasonic Pretreatment on the Extraction Process of Essential Oils from Grapefruit (Citrus paradisi) By-Products.

This study evaluated the effect of ultrasonic pulse-assisted extraction on the yield and antioxidant activity of essential oils from grapefruit (Citrus paradisi) by-products using hydrodistillation and Soxhlet solvent extraction (hexane, acetone, ethanol). Ultrasound was applied at 40% amplitude for 20 min before extraction. Results showed that ultrasound significantly increased extraction yield with hexane (from 2.6 ± 0.58% to 7.6 ± 1.5%) and acetone (from 8.6 ± 0.96% to 12 ± 1.4%), while ultrasound-assisted hydrodistillation nearly doubled the yield (from 0.7 ± 0.03% to 1.5 ± 0.49%). In contrast, ultrasound decreased yield with ethanol by 3%. Antioxidant activity measured by TEAC assay was highest in acetone extracts without ultrasound (13,366.5 ± 7.66 mmol TE/g) and ethanol extracts (12,606.8 ± 0.51 mmol TE/g). However, ultrasound combined with ethanol increased DPPH scavenging activity from 1073.5 ± 1.07 µg/mL to 4933.3 ± 0.71 µg/mL and maintained high flavonoid content (9.41 ± 0.15 mg/mL) and phenolics (5.33 ± 0.09 mg/mL). Ultrasound-assisted hydrodistillation also enhanced antioxidant capacity, with DPPH values rising from 51.82 ± 5.56 µg/mL to 2413.03 ± 3.17 µg/mL. These findings demonstrate that ultrasound effectively enhances essential oil extraction and antioxidant activity depending on the solvent used, underscoring the potential of this clean technology for valorizing citrus by-products.