Table 4.

Summary of the main recent findings showing the effects of the ultrasound (US) technology on anthocyanin extraction from agri-food by-products.

Waste/By-Product	Extraction Process Parameters	Major Findings	Reference
Blueberry peel	Ultrasound nominal power: 100 and 500 W Processing time: 40 min Temperature: 40 °C Solvent: Five natural deep eutectic solvents Ultrasonic equipment: Probe at 20 kHz	-The US-based extraction technique achieved 21.18 mg/g total anthocyanin content after 30 min of sonication at 500 W power while conventional extraction based on a stirring and heating system extracted 22.70 mg/g after 2 h at 55 °C and 200 rpm.	[121]
Blueberry pomace	Ultrasound nominal power: 400 W Processing time: 15–35 min Temperature: 50–70 °C Solvent: Acidified hydroethanolic mixture (70% ethanol) Ultrasonic equipment: Probe	-Delphinidin-3-O-glucoside, delphindin-3-O-arabinoside, petunidin-3-O-glucoside, cyanidin-3-O-arabinoside, cyanidin-3-O-glucoside, malvidin-3-O-glucoside, and malvidin-3-O-arabinoside were recovered; -Compared to conventional solvent extraction, US-assisted extraction resulted in higher anthocyanin recovery.	[169]
Jabuticaba by-product	Ultrasound intensity: 1.1–13.0 W/cm² Processing time: 3 min Solvent: Hydroethanolic mixtures (0–100% ethanol) Ultrasonic equipment: Probe at 19 kHz with a diameter of 13 mm	-The higher ultrasound intensities presented the lowest values for bioactive compounds and antioxidant capacity; -Extracts presented a brownish color indicating degradation of their compounds and loss of color due to the increase in the cavitation effect; -Solvent composition had a strong influence on anthocyanin recovery.	[53]
Jabuticaba by-product	Power density: 50 and 60 W/L Processing time: 10–40 min Solvent: Acidified water (pH 1.5, 3.0, and 7.0) Ultrasonic equipment: Ultrasound bath at 25 and 40 kHz	-Ellagic acid and cyanidin-3-O-glucoside were the major phenolic compounds extracted from jabuticaba by-product; -Processing time and solution pH were the most significant variables.	[167]
Black chokeberry waste	Ultrasound nominal power: 0–100 W Processing time: 0–240 min Temperature: 20–70 °C Solvent: Hydroethanolic mixtures (0–50% ethanol) Ultrasonic equipment: Ultrasound bath at 30.8 kHz	-At high temperatures, anthocyanin yield was decreased with processing time suggesting their thermal degradation.	[54]
Blackberry waste	Ultrasound nominal power: 1500 W Processing time: 15 min Temperature: 4 °C Solvent: Water Ultrasonic equipment: Probe at 20 kHz with a diameter of 25 mm	-Ultrasonicated blackberry waste had low antioxidant compounds compared to blackberry waste. However, these compounds showed a high in vitro bioaccessibility.	[170]
Blackberry by-product	Ultrasound nominal power: 580 W Processing time: 90 min Temperature: 80 °C Solvent: Hydroethanolic mixtures (50% and 70% ethanol) and acidified water (pH 2) Ultrasonic equipment: Ultrasound bath at 37 kHz	-Hydroethanolic mixtures were more efficient to extract anthocyanins; -Cyanidin-3-O-glucoside, cyanidin-3-O-rutinoside, cyanidin-3-O-malonyl-glucoside, and cyanidin-3-O-dioxalylglucoside were identified in the extracts.	[52]
Pomegranate by-product	Ultrasound nominal power: 70–210 W Duty cycle: 20–80% Processing time: 1–10 min Solvent: Hydroethanolic mixture (50% ethanol) Ultrasonic equipment: Probe at 20 kHz	-The pulsed US-assisted extraction of bioactive compounds from pomegranate peel was an emerging green, energy, and time-efficient extraction process for the extraction of food bioactives; -Multicriterial numerical optimization suggested 116 W sonication power with 80% duty cycle for 6 min for extraction of 22.51 mg cyanidin-3-glucosides/100 g pomegranate peel.	[171]
Eggplant by-product	Ultrasound nominal power: Not specified Processing time: 15–45 min Temperature: 25 and 50 °C Solvent: Acidified hydroethanolic mixtures (70% and 96% ethanol) Ultrasonic equipment: Ultrasound bath	-Five anthocyanins were identified: delphinidin-3-O-rutinoside-5-glucoside, delphinidin-3-O-glucoside, delphinidin-3-O-rutinoside, cyanidin-3-O-rutinoside, and petunidin-3-O-rutinoside; -US-assisted extraction was preferable to conventional solid-liquid extraction due to the lower temperature used and higher delphinidin 3-O-rutinoside content.	[41]
Eggplant by-product	Ultrasound nominal power: Not specified Processing time: 15–45 min Temperature: 50–70 °C Solvent: 50–90% (v/v) methanol or 2-propanol in water Ultrasonic equipment: Ultrasound bath at 12.5, 25, and 37.5 kHz	-Solvent concentration exhibited a negative effect on the anthocyanin content; -Ultrasonic frequency, processing time, and extraction temperature had a positive effect on the anthocyanin recovery.	[172]
Grape pomace	Ultrasound nominal power: 150–300 W Processing time: 2.5–10 min Temperature: 25–55 °C Solvent: Water Ultrasonic equipment: Probe at 20 kHz with a diameter of 13 mm	-The aqueous extracts of grape by-product presented higher levels of antioxidant capacity (1.4-fold), anthocyanins (1.3-fold), and total phenolic (1.2-fold) by comparing with the conventional extraction technique.	[173]
Raspberry by-product	Ultrasound nominal power: 100–500 W Pectinase dosage: 0.05–0.25% Processing time: 10–50 min Temperature: 40–60 °C Solvent: Acidified hydroethanolic mixture (60% ethanol) Ultrasonic equipment: Probe	-Cyanidin-3-glucoside with a purity of 93.46% and cyanidin-3-rutinoside with a purity of 94.16% were obtained from raspberry by-products; -The optimum extraction parameters were obtained at 44 °C, 290 W, 30 min, and pectinase dosage of 0.16%.	[166]
Mulberry by-product	Ultrasound nominal power: 200–400 W Pectinase dosage: 0.15–0.25% Processing time: 60–120 min Temperature: 40–60 °C Solvent: Acidified water Ultrasonic equipment: Ultrasound bath	-The optimum extraction conditions were 52 ℃, 315 W, 94 min, and enzyme dosage of 0.22%; -Cyanidin-3-O-glucoside and cyanidin-3-O-rutinoside are the two main anthocyanins in mulberry by-product.	[55]
Peach waste	Ultrasound nominal power: 80–400 W Processing time: 20–120 s Temperature: 25–55 °C Solvent: Hydroethanolic mixture (70% ethanol) Ultrasonic equipment: Probe at 24 kHz with a diameter of 10 mm	-Lower ultrasound powers and longer processing times contributed to a greater anthocyanin recovery.	[127]