Ultrasound-Assisted Extraction of Phenolic Compounds and Flavonoids from Banana Inflorescence and Characterization of Its Fibrous Residue

The banana inflorescence (BI) is a rich source of antioxidants and dietary fiber, making it a valuable by-product of banana harvesting. This study aimed to maximize the ultrasound-assisted extraction (UAE) of antioxidant compounds from BI and analyze the residue’s composition and functional properties. The Box–Behnken Design was applied to test different ultrasound powers, temperatures, and sample-to-solvent ratios on the total phenolic content (TPC) and total flavonoid content (TFC). The UAE conducted at 350 W, 55 °C, 1:30 (g/mL) ratio for 30 min resulted in the highest TPC (1637.12 mg/100 g) and TFC (22.97 mg/100 g). Isovanillin, caffeine, naringin, sinapaldehyde, nicotinic acid, quinic acid, malic acid, and fumaric acids were reported for the first time for BI. The extract obtained by UAE showed a higher content of these compounds and higher antioxidant activity than that obtained through conventional extraction (orbital shaking). The residue obtained after UAE presented dietary fiber as the main component (71.91 g/100 g) and a higher oil absorption index (5.78 g/g) than untreated BI. Therefore, BI is a source of bioactive compounds, and both the extract and residue can be used in the pharmaceutical, food, and cosmetic industries, enabling the productive sector to move closer to the circular economy.