Chemical composition and antibacterial activity of Azadirachta indica seed oil from Chad

Abstract

This study focuses on extracting oil from the seeds of the Azadirachta indica species A. Juss, known in Chad as mim or neem, utilizing a cold-press extraction method. It aims to characterize the oil's chemical composition through Gas Chromatography-Mass Spectrometry (GC-MS) analysis and evaluate its antibacterial efficacy using the well diffusion and microdilution techniques. The antibacterial potential was assessed against four food-borne pathogens: Staphylococcus aureus, Methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli, Salmonella sp., and a soil bacterium, Bacillus subtilis. The results from the GC-MS analysis indicated a predominant presence of fatty alcohols, notably Stigmasta-3,5-diene (49.00%), a steroid alcohol, and Tetradecen-11-yn-1-ol (35.37%), a long-chain fatty alcohol. Additionally, lesser quantities of compounds such as (E, E)-7,11,15-Trimethyl-3-methylene-hexadeca-1,6,10,14-tetraene (a diterpene) at 9.68%, Squalene (a triterpene) at 1.77%, and 2,4,4-Trimethyl-3-hydroxymethyl-5a-(3-methyl-but-2-enyl)-cyclohexene (a sesquiterpene) at 4.19% were identified. The analysis showed that neem oil is rich in fatty alcohols and phytosterols, with lower terpenes and phenolic compounds. It showed no significant antibacterial activity against the tested bacteria. This suggests that from cold-press extraction, neem oil may not effectively combat food-borne pathogens and soil bacteria due to its fatty alcohol and phytosterol content, along with the bacteria's resistance. Increasing the concentration of crude oil in the antibacterial test could lead to positive results. The findings indicate a need for further research to isolate stronger antibacterial molecules in neem oil by separating its components, focusing on extraction methods and solvent polarity.