Liquid chromatography-mass spectrometry-based metabolomics of oil palm (Elaeis guineensis jacq.) leaf

The profiling and characterization of plant metabolome provide depiction of its metabolic events and permit the harnessing of valuable chemicals. However, the effort is often hindered by their structural complexity. The oil palm leaves are the most abundant by-product of the oil palm sector but the usage of the waste is marginal. Researches that facilitate its efficient utilization are necessary to sustain the industry. As phenotypes of organisms are not direct representations of their genotypes and are largely influenced by their environment, ecological metabolomics is required to capture metabolite shifts in response to external factors. An immediate chemical description of the oil palm leaves metabolome was achieved using liquid chromatography (LC) combined with mass spectrometry (MS). Commercial standards were unavailable for most of the chemicals, thus, mass spectrometry with data mining techniques such as neutral loss analysis aided the identification of compounds. The metabolome of oil palm spear leaf was compared to that of mature oil palm frond using both positive and negative ion mode. The spear leaf contains seven apigenin glycosides-hydroxymethylglutaric acid complexes and an O-glycosylated apigenin that were not present in the frond tissue. Conversely, four luteolin glycosides and two isomers of apigenin diglycosides were absent in the spear leaf sample. A total of 53 compounds including metal salt complexes, amino acids,amines, organic acids, catechins, phenolic acid glycosides, flavonoid glycosides and a stilbenoid glycoside in the oil palm leaves were identified in this work. The oil palm leaves extracts exhibited good antioxidant activities with the frond tissue demonstrated the highest DPPH radical scavenging activity value per g of leaf tissue dry weight,followed by the hydrolyzed fraction of frond extract, hydrolyzed spear leaf extract and spear leaf extract. The metabolome of oil palm clones were influenced by their planting conditions regardless of their genotypes. Organic acids, amino acid and dihydroxyphenethylamine isomers discriminated the clones grown under different planting conditions. LC-MS proved to be an effective, sensitive and rapid technique in acquiring information that to-date has been scarce for this important species. The profiling of oil palm leaves provided essential information on the chemical properties of the tissue that will in turn promote utilization of the waste. Principal component analysis (PCA) aided the assessment of oil palm status and paved ways to more ecological investigations in oil palm researches.

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