Biogenic synthesis of ZnO and NiO nanoparticles mediated by fermented Cocos nucifera. (L) deoiled cake extract for antimicrobial applications towards Gram Positive and Gram Negative pathogens

Abstract Background Cocos nucifera (L) is a widespread tall plant and found to havelot of important pharmacological applications and it is very less toxic in nature. The water of the endocarp has high antioxidant activity, and its fiber was reported to have antibacterial, ant parasitic and anti-inflammatory properties. The oil derived from its edible parts have been used in cooking, in the preparation of the soaps and cosmetics etc. The water within can be processed to produce alcohol. Once the endocarp was crushed and the extract were removed it can used as a feed material and as a natural organic fertilizer. Herein, we report the novel method of utilizing the residue of the deoiled seed cake of Cocos nucifera (L) for preparing the metal oxides as a reducing agent and to test its antimicrobial level against human pathogens. Methods The method adopted in this investigation is the fermentation process of preparing the Cocos nucifera (L) extract by utilizing the water as the medium for the extraction process under room temperature. Results Structural nature and morphology of the synthesized samples were carried out using XRD and SEM analysis and the results revealed that ZnO belongs to hexagonal shape with primitive lattice cell arrangement and NiO had cubic structure with FCC lattice arrangements. The results of the average crystalline size of prepared nanoparticles using XRD and SEM were alike. Molecular bonding and stability were analyzed using FTIR instrumentation based on UV absorption and Tauc plot the bandgap of ZnO and NiO was calculated as 3.15 eV and 3.64 eV. Elemental composition was identified using EDAX analysis. Antibacterial assay was carried out against human pathogens including S.aureus, B.subtilis, E.coli and K.pneumoniae in comparison to the standard drug Gentamycin and the synthesized specimens ZnO and NiO showed the moderate activity with the zone of inhibition of about of 8 mm, 10 mm, 12 mm and 8 mm against the human pathogens. Conclusion Our results showed that the antimicrobial properties of the Cocus nucifera (L) mediated ZnO and NiO have moderate activity against the standard drug Gentamycin, three different doses were tested against the disease causing pathogens including S.aureus, B.subtilis, E.coli and K.pneumoniae. The zone of inhibition was found to be minimum. This may be attributed to the reason that even after the removal of the edible compounds from the seed of Cocos nucifera (L), the residue or the waste product found to have a moderate antimicrobial function against pathogens.