Optimizing the extraction of ursolic acid from loquat leaf using ¹H-qNMR

Ursolic acid (UA) has a wide range of biological activities and is extracted primarily from natural products. However, conventional quantification methods require derivatization or chromatographic separation, which are tedious and time-consuming. In this study, a rapid and accurate quantitative proton nuclear magnetic resonance (¹H-qNMR) method was established for the direct quantification of UA in loquat leaf extracts. By optimizing the NMR acquisition parameters, 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 the purity and yield of UA crude extract. Results indicated that the optimal conditions involved the low-temperature extraction of loquat leaves (sample concentration: 0.03 g mL^-1) 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.