Valorisation of Lemongrass (Cymbopogon citratus) Leaf By-product as a Source of Essential Oil

This research aimed to investigate the potential of lemongrass (Cymbopogon citratus) leaf agricultural by-products as a source of essential oil, and evaluate the antioxidant and antibacterial activities. In this context, the material used was subjected to microwave pre-treatment to enhance the yield. Lemongrass leaf was often discarded as an agricultural by-product. The utilization was examined through different drying methods, including fresh, wilted, and dried treatments. Lemongrass leaf was also treated with microwave (+MV) and non-microwave (-MV) pre-treatments. The essential oils were analysed for physicochemical properties. The chemical composition was determined through gas chromatography-mass spectrometry (GC-MS), and the tissue microstructure was observed by SEM. Antioxidant activity was measured with the DPPH (1,1-diphenyl-2-picrylhydrazyl) assay, while MIC and MBC values were assessed using the microdilution method. The results showed that the distillation of dried leaf with microwave pre-treatment provided the highest oil yield of 0.20%. SEM analysis showed that drying and microwave pre-treatment altered the leaf microstructure, enhanced glandular trichomes, and improved extraction efficiency. The physicochemical properties included a bright yellow colour, a fresh citrus aroma, a specific gravity of 0.971 g/mL, a refractive index of 1.486, and a solubility ratio of 1:3 in alcohol. The main components were citral (geranial (44.07–46.81%), neral (35.64 – 36.60%)), geranyl acetate (2.03–5.66%), isogeranial (1.61–2.57%), isoneral (0.96–1.76%), β-pinene (0.16–3.63%). Lemongrass leaf oil exhibited strong antioxidant activity with an IC50 of 61.65 to 84.5 µg/mL, antibacterial activity against E. coli and S. aureus with MIC of 0.3–1.3% and 0.3–1.8%, as well as an identical MBC value of 0.5–2% for both bacteria. This research showed that essential oil extraction increased the value of lemongrass leaf by-products.