Optimizing Extraction of Ursolic Acid From Loquat Leaf Using 1H-qNMR

Abstract

Ursolic acid (UA) has a wide range of biological activities and is primarily extracted from natural products. However, conventional quantification methods require derivatization or chromatographic separation, which are tedious and time-consuming,. Herein, a rapid and accurate quantitative proton nuclear magnetic resonance (¹H-qNMR) method was established for direct quantification of UA in loquat leaf extracts. By optimizing NMR acquisition parameters, the ¹H-qNMR achieved a single-sample runtime of 5 min with high accuracy and precision. This method was also applied to optimize UA extraction from Loquat leaves, systematically evaluating the effects of temperature, extraction solvent, solid-to-liquid ratio, and extraction time on UA crude extract purity and yield. Results indicated that the optimal conditions were low-temperature extraction of loquat leaves (sample concentration: 0.03 g/mL) with ethanol at 0 °C for 48 h, which afforded an average UA crude purity of 33.68% and an extraction yield of 0.84%, outperforming Soxhlet extraction. This study confirms that ¹H-qNMR enables rapid quality control of UA in Loquat and provides a simple, reliable analytical strategy for optimizing extraction processes of bioactive compounds in other complex botanicals.