Quality of African moringa (Moringa stenopetala) leaf samples by liquid chromatography of phenolics, loss on drying and ash content

The aim of this study was to evaluate the quality of African moringa (Moringa stenopetala) leaf preparations using easily applicable analytical methods. For this purpose, a novel simple and fast LC-UV method was developed and validated to determine the most common phenolic compounds. The method showed good linearity with determination coefficients (r(2)) >= 0.999. Detection limits were below 0.4 mu g/ml and quantification limits below 1.2 mu g/ml. Relative standard deviation (RSD) values for intra- and inter-day precision were less than 2% and recoveries were close to 100%. Robustness of the method was evaluated using an experimental design. The developed method was applied to analyze some commercial moringa leaf samples obtained from Ethiopia. Unknown compounds were tentatively identified as neochlorogenic acid and kaempferol 3-O-rhamnosylglucoside (KRG) by means of mass spectrometry (MS). Rutin was found to be the most common compound. Its content in samples varied from 2 to 18 mg/g. The amounts of (neo)chlorogenic acid and KRG were less than 2 mg/g, while quercetin and caffeic acid were not detected. The method allowed to observe differences in phenolic composition between regions. Results for loss on drying and ash content revealed that 40% and 50%, respectively, of the samples were not compliant. Novelty Impact Statement Quality control of formulations of Moringa stenopetala leaves is as good as non-existent due to lack of suitable test procedures. The analytical methods proposed here are easily applicable in low-income countries and include a novel LC-UV method for the phenolic compounds, loss on drying, and ash contents. The combined tests were found to be successful in differentiating the quality of different commercial samples.