NMR-based metabolomic analyses to identify the effect of harvesting frequencies on the leaf metabolite profile of a Moringa oleifera cultivar grown in an open hydroponic system

Moringa oleifera Lam. is one of the world’s most useful medicinal plants. Different parts of the M. oleifera tree contain a rich profile of important minerals, proteins, vitamins, and various important bioactive compounds. However, there are differences in the phytochemical composition of the medicinal plant’s raw materials due to seasonal variation, cultivation practices, and post-harvest processing. The main objective of this study was therefore to determine the effect of harvesting frequencies on selected bioactive compounds of a M. oleifera cultivar (PKM1) grown in a hydroponic system under a shade net structure. Three harvesting frequency treatments were applied in the study, with the plants harvested at every 30 days (high frequency), 60 days (intermediate frequency), and 90 days (low frequency) respectively. 1H-NMR was used for data acquisition, and multivariate data analysis by means of principal component analysis (PCA), partial least square discriminatory analysis (PLS-DA), and orthogonal partial least square discriminatory analysis (OPLS-DA) were applied to determine the changes in the leaf metabolite profile, and also to identify the spectral features contributing to the separation of samples. Targeted metabolite analysis was used to match the NMR peaks of the compounds with the NMR chemical shifts of the contribution plot. The contribution plot showed that the increase in concentration of some compounds in aliphatic, sugar and aromatic regions contributed to the separation of the samples. The results revealed that intermediate and low harvesting frequencies resulted in a change in the leaf metabolite profile. Compounds such as chlorogenic acid, ferulic acid, vanillic acid, wogonin, esculetin, niazirin, and gamma-aminobutyric acid (GABA) showed an increase under intermediate and low harvesting frequencies. These results provide insight into the effect of harvesting frequencies on the metabolite profile and associated medicinal activity of M. oleifera.SUPPLEMENTARY MATERIAL: FIGURE S1: Contribution plot showing metabolite peaks in the NMR aliphatic, sugar and aromatic regions of M. oleifera leaf metabolomics associated with March sample separation under high harvesting frequency as shown in Figure 2, FIGURE S2: OPLS-DA loading score plot showing 1H-NMR spectral data of M. oleifera (cultivar PKM1) metabolite profile under low/ intermediate and high harvesting frequency, FIGURE S3: PLSDA score plot showing 1H-NMR spectral data of M. oleifera (cultivar PKM1) metabolite profile under low/intermediate and high harvesting frequencies, showing separation between day 0 and end point harvesting, FIGURE S4: PLS-DA model validity permutation test for M. oleifera (cultivar PKM1) metabolite profile under low, intermediate and high harvesting frequencies, TABLE S1: 1H-NMR spectral regions of annotated compounds that contributed to the separation of leave samples.The National Research Foundation (NRF)-Competitive Programme for Rated Researchers, University of Pretoria (UP), University of South Africa (UNISA), and Human Sciences Research Council (HSRC).https://www.mdpi.com/journal/moleculesam2022Plant Production and Soil Scienc