Valorization of Asparagus leafy by-product by ionic-liquid extraction and characterization of bioactive compounds in the extracts

Asparagus (Asparagus officinalis) is a high-value low-calorie vegetable with array of bioactive compounds. Asparagus processing nevertheless generates substantial quantity of by-products; their valorization is of utmost importance for the sustainability of the industry. Here, feasibility of using four imidazolium-based ionic liquids and their combinations as well as water and methanol to extract bioactive compounds from asparagus leafy by-product was investigated. Effectiveness of ultrasound-microwave-assisted heating to augment extraction was also assessed. 1-ethyl-3-methylimidazolium-bromide (EMIMBr) resulted in the highest extraction yield of rutin (25.7 mg/g), which is the most abundant compound in the by-product; such a yield was comparable to that achievable via methanol extraction. Ultrasound-microwave-assisted extraction did not show significant improvement in rutin yield when EMIMBr was used. Interestingly, although methanolic extract exhibited slightly higher content of rutin, it also contained the higher number of impurities; EMIMBr extract contained less impurities with higher relative content of rutin (70.9%) than that in methanolic extract (67.7%). This could be a milestone in extraction work for an efficient purification.