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

Abstract

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 (r2) ≥ 0.999. Detection limits were below 0.4 μg/ml and quantification limits below 1.2 μg/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.

Fast RP-HPLC Method for Analysis of Glucosinolates and Phenolics in Moringa stenopetala Leaf Powder Preparations

“…The average content of rutin, the principal component, ranged from 6.6 mg/g to 18.8 mg/g. This finding was comparable with results reported elsewhere [4,28] i.e., 2.3% (or 23 mg/g) of rutin in M. stenopetala leaves and significantly higher than those published in [6,16] which were 3.0 mg/g (highest in young leaves) and 1.155 mg/g (in methanol extract), respectively. Moreover, the content of neochlorogenic acid varied from 0.2 to 3.6 mg/g while the content of chlorogenic acid ranged from 0.2 mg/g to 2.7 mg/g.…”

“…Peak 3 showed a deprotonated ion [M − H]at m/z 353 and MS/MS fragments at m/z 191 and m/z 179, the latter with low intensity. A similar pattern was observed for neochlorogenic acid as discussed more in detail in reference [28].…”

“…Peak 5, which was also common to all the samples, showed a molecular ion [M -H] − at m/z 353 and fragment ions at m/z 191, m/z 179 and m/z 135, similar to chlorogenic acid described in reference [28] where the interpretation is discussed more in detail. Further confirmation was obtained by comparing the LC and MS data with a reference compound of chlorogenic acid.…”

“…Peak 6, which was the most abundant peak in all samples, yielded a [M -H] − at m/z 609 and an MS/MS fragment ion at m/z 300. Further fragmentation resulted in ions at m/z 271, m/z 255, m/z 179 and m/z 151, corresponding to those of rutin as reported more in detail in reference [28]. Since the retention time was also comparable with the standard, peak 6 was identified as rutin.…”