ABSTRACT
The identification and subsequent quantification of phenolic compounds in plants is the first step toward harnessing their associated nutritional and health benefits. Due to their diverse phenolic compound compositions, grain legumes are known for their high nutritional and health values. The aim of this study was to assess the inter-variations in chemical composition, phytochemical content, and antioxidant capacity of seed extracts from eight Kersting's groundnut [Macrotyloma geocarpum (Harms) Marechal & Baudet] landraces. The chemical profiles were evaluated using UPLC-qTOF-MS. Total phenolics and flavonoids content were determined by the Folin-Ciocalteu and aluminum chloride methods, respectively. The antioxidant capacities in the forms of DPPH and ABTS were evaluated using spectrophotometric methods. Principal component analysis was used to define similarities/differences between the landraces. Based on untargeted metabolomics analysis, 57 metabolites were identified, with phenolics, triterpenes, fatty acids, and sphingolipids being the most predominant. The results showed that the black seeded KG1 (Puffeun) had the highest total phenolic (9.44 mg GAE/g) and flavonoid (3.01 mg QE/g) contents, as well as antioxidant capacity (9.17 µg/mL and 18.44 µg/mL based on DDPH and ABTS assays, respectively). The concentrations of ferulic acid hexoside, procyanidin B2, eryodictyiol-7-rutinoside and quercetin pentoside ranged from 51.78-441.31, 1.86-18.25, 3.26-13.95 to 5.44-63.85 µg/mg, respectively. This study presents a useful report on the phytochemical characterization of Kersting's groundnuts and shows that the grains can be used as a source of nutraceuticals for human consumption.
ABSTRACT
Bambara groundnut is one of the under-utilized African legume crops, valued for its nutritional and health benefits, and for which ongoing studies will help to distinguish its many landraces and select the promising one for breeding programs. To describe the polar metabolome of the seed from 21 Bambara groundnut landraces, untargeted metabolomics approach using UPLC-qTOF-MS (Ultra performance liquid chromatography-Quadrupole time of flight mass spectrometry) was performed. Metabolites belonging to varied compound classes were detected and identified. The total phenolic, flavonoid and anthocyanin contents varied from 0.75 to 17.71â¯mg GAE.g-1, 0.01 to 2.51â¯mg QUE.g-1 and 0.03 to 1.31â¯mg CYE.g-1, respectively. Unsupervised statistics highlighted differences in the metabolome of different landraces. Principal component analysis revealed that caffeic and catechin conjugates are the most decisive marker compounds discriminating the landraces. This study provides the most complete map of metabolites in Bambara groundnut seeds and demonstrates that UPLC-qTOF-MS coupled with chemometric is an excellent tool for differentiation between landraces. These findings highlight the potential of Bambara groundnuts as an economic source of natural antioxidants for human consumption and food industries, and therefore open horizons to the industrial use of Bambara groundnut flours in the development of functional food and feed products.
Subject(s)
Antioxidants/metabolism , Chromatography, High Pressure Liquid , Metabolomics/methods , Phytochemicals/metabolism , Seeds/metabolism , Spectrometry, Mass, Electrospray Ionization , Vigna/metabolism , Anthocyanins/metabolism , Flavonoids/metabolism , Phenols/metabolism , Seeds/classification , Vigna/classificationABSTRACT
Although nitrate is known to inhibit nodulation and N2 fixation in symbiotic legumes, little is known about its effect on the uptake and accumulation of trace elements such as Fe, Zn, Mn and Cu. The aim of this study was to evaluate the effect of 5 mM NO3- supply, either with or without rhizobial inoculation, on nodulation, nodule functioning and micronutrient levels in the shoots of soybean (Glycine max L.Merr.), Bambara groundnut (Vigna subterranea L. Vedc) and Kersting's groundnut (Macrotyloma geocarpum Harm). The results showed reduction in plant growth, nodule formation and nodule dry matter by the supply of 5 mM NO3- to inoculated seedlings of all three species. Nitrate inhibition respectively caused 1.2, 1.4, and 1.5-fold decrease in nodule number per plant in Bambara groundnut, soybean and Kersting's bean, which resulted in 2.3, 3.3 and 4.5-fold reduction in nodule dry weight of the test species (in that order). The application of 5 mM NO3- to soybean plants also resulted in 2.5, 4.0 and 5.4-fold decrease in shoot accumulation of Fe, Zn and Mn, respectively, when compared to the purely symbiotic control plants. Furthermore, we observed 1.3, 1.8 and 1.3-fold decreases in the concentration of Zn, Mn and Cu in shoots of inoculated Bambara groundnut with NO3- supply, levels lower than those found in soybean. With Kersting's groundnut, shoot concentration of Fe, Zn and Cu were higher with the application of 5 mM NO3- to inoculated plants when compared to the purely symbiotic treatment, which was opposite to soybean. But pure NO3-feeding of this species respectively resulted in 2.0, 1.4 and 1.3-fold decreases in Fe, Zn and Cu relative to inoculated NO3--fed plants. Clearly, NO3- supply to landraces/genotypes of the three legume species did not only inhibit nodule formation and functioning, it also reduced shoot micronutrient levels in soybean and Bambara groundnut, but not Kersting's bean.
