Evaluation of Antimicrobial, Antioxidant and Biocompatibility of Coconut Oil Based Bar Soap Infused with Selected Herbal Extracts

Abstract

Human-associated bacteria live on the skin and are harmless or have a symbiotic relationship with the host. Since the skin surface has limited nutrients for the survival of these bacteria, there is competition which results in a delicate balance of the microbes. This leads to various skin infections as different microbes use different mechanism to eliminate their competitors. The skin is also affected by exogenous free radicals from pollutants or ultraviolet (uv) radiations causing the skin cells to have oxidative stress. The products available for the prevention and treatment of these infections are those produced with synthetic materials that are harmful to both human and the environment. Therefore, the shift to the use of herbal products. In this study, the functional groups and the class of compounds in methanol and aqueous crude extracts of the leaves of Terminalia catappa L. and Ziziphus robertsoniana B. were analyzed using Fourier transform infrared spectrophotometer (FT-IR) and Gas Chromatography-mass (GC-MS) spectroscopy. The disk diffusion assay was used to evaluate the antimicrobial activities while the minimum inhibition concentration (MIC) was determined using micro-broth dilution assay. The antioxidant activities were determined through 2,2-diphenyl-1-picrylhydrazyl (DPPH) and Potassium Ferricyanide Reducing Antioxidant Power (PFRAP). The cytotoxic effects of the plants’ extracts were determined using brine shrimp and 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) assays. The phytochemical screening revealed the presence of tannins, saponins, phenols, alkaloids, flavonoids, steroids, terpenoids, and cardiac glycosides. Characteristic functional groups such as OH, C-O, C=O, and C=C were identified by FTIR and are associated with compounds such as tannins, saponins, and terpenoids. GC-MS analysis revealed the presence of diterpenoids such as phytol which have been reported to have antimicrobial and antioxidant properties. The crude extracts and positive controls exhibited antimicrobial activities against Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and the fungus Candida albicans with diameters of zone of inhibitions ranging between 0 to 25.7 mm. The extracts demonstrated antioxidant activities which was concentration dependent. The methanol extract of T. catappa exhibited lethality concentration at 50% (LC50) value of 0.077 mg/mL while that of Z. robertsoniana methanol extract gave a value of 0.069 mg/mL. The physical-chemical tests done on the formulated soaps showed compliance as per the international standard. Incorporation of the crude extract in formulated soap imparted a concentration-dependent antioxidant, with the IC50 values of soaps infused with T. catappa aqueous, T. catappa methanol, Z. robertsoniana extracts and extract free were 674, 725.7, 1767 and 992.5 µg/mL respectively. The lower the IC50, the better the antioxidant activity as less amount of the test soap is needed to reduce the free radicals of the DPPH solution. The antimicrobial activity of the formulated soaps had varying zones of inhibitions ranging from 10 to 20 mm while those of the control soap ranged from 6.67 to 11.67 mm for all the tested microbes. The antimicrobial and antioxidant properties were linked to the identified phytochemical compounds. Therefore, the study findings demonstrated T. catappa and Z. robertsoniana leaves extracts as effective raw materials for formulation of the soaps with antimicrobial and antioxidant properties.