Deep Eutectic Solvents for Efficient and Selective Extraction of α-Glucosidase Inhibitors from Waste Seeds of Refined Betel Nuts

During the production process of refined betel nuts in China, a large amount of processing by-product, betel nut waste seeds, is generated. Betel nut waste seeds are rich in bioactive elements, but they have not been effectively utilized yet. In this study, an ultrasonic-assisted deep eutectic solvent method (DES) was used to selectively extract α-glucosidase inhibitors from waste seeds. Compared with traditional extraction solvents such as water and ethanol, the extraction efficiency of specific DESs is higher, and the content of alkaloids in the extracts is lower. However, it should be noted that some pure DESs exhibit inhibitory activity towards α-glucosidase. DESs, based on choline chloride/urea, were selected due to the high extraction efficiency of α-glucosidase inhibitors and their low alkaloid content as well as low inhibitory activity. The optimal extraction conditions were determined using single-factor experiments as follows: 30% (v/v) water content, a choline chloride/urea ratio of 5:3, a solid-liquid ratio of 1:10, extraction temperature of 40 °C, and a duration of 30 min. Through recovery experiments, it was found that the DES can be reused four times under these conditions, maintaining an inhibition rate comparable to alcohol extraction methods. The IC₅₀ value of the extract was measured at 0.0066 mg/mL, superior to acarbose. In summary, this research has successfully developed an efficient and selective method for extracting α-glucosidase inhibitors from betel nut waste seeds, thereby presenting a promising avenue for future applications.