Ultrasound-Assisted DES Extraction of Black Rice Anthocyanins: Optimization, Characterization, and Bioactivity

Black rice is a rich source of anthocyanins, which exhibit strong antioxidant properties and potential hypoglycemic effects. However, the application of black rice and related bioactive compounds in the food and functional food industries is limited by low extraction yields. Therefore, to promote the potential applications of black rice as a value-added health product, the extraction, characterization, and evaluation of the beneficial effects of anthocyanins from black rice were examined in the present study. A green and efficient ultrasound-assisted deep eutectic solvent extraction (UDE) method for extracting anthocyanins from black rice was established. Under the optimum conditions (choline chloride-lactic acid as DES with a mole ratio of 1:2.06, solid-to-liquid ratio of 1:19.8 g/mL, water content of 39.8%, and ultrasonic temperature of 50.8°C), a maximum yield (37.44 ± 0.04 mg/g) of anthocyanin extracted from black rice by UDE was obtained, which was significantly higher than ultrasound-assisted ethanol extraction (UEE). LC‒MS analysis confirmed cyanidin-3-glucoside as the predominant component. In addition, compared with UEE, UDE exhibited much higher antioxidant effects as well as inhibitory effects against α-glucosidase and α-amylase. Collectively, the findings suggest that the UDE method can be applied as an efficient technique for the preparation of anthocyanins from black rice. PRACTICAL APPLICATIONS: The optimized DES-UAE extraction protocol directly addresses the bottleneck of low extraction yields associated with black rice anthocyanins, offering a highly efficient and safer alternative to conventional ethanol-based methods by circumventing flammability and regulatory constraints. By avoiding the chemical degradation typically caused by traditional organic solvents, this green approach yields C3G-enriched extracts with their inherent chemical integrity and bioactivity well-maintained. Specifically, leveraging their demonstrated inhibitory effects against α-glucosidase and α-amylase, these extracts can be directly formulated into targeted dietary supplements for blood glucose management. Additionally, their robust antioxidant profile makes them suitable as clean-label natural colorants for functional foods. Ultimately, this method provides a practical processing route for converting underutilized black rice into value-added health products, supporting green manufacturing practices at the laboratory and pilot scales.