Antimicrobial Activity of African Walnut (<em>Tetracarpidium conophorum</em>) Oil against Bacterial and Fungal Species Causing Food Spoilage and Food Poisoning Diseases

Abstract

This study evaluated the antibacterial and antifungal activity of African walnut (Tetracarpidium conophorum) oil against species causing food poisoning and food spoilage. African walnut oil was extracted using the solvent extraction method. The fatty acid profile of the oil was determined using gas chromatography mass spectrometry (GC-MS). The agar disc diffusion method was used to determine the antibacterial activity of the oil before using it for further tests. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were also determined using the disc diffusion assay. The result indicates that palmitic (1.53%), linoleic (13.5%), linolenic 80.59%, stearic (4.41%), and eicosenoic acid (0.42%) were present in the oil with higher polyunsaturated fatty acid values. African walnut oil showed remarkable activity against all the Gram positive organisms (Bacillus cereus ATCC 33018, Staphylococcus aureus ATCC 25923, Clostridium perfringes NCTC 8799, and Listeria monocytogenes ATCC 13932) with the inhibition zones ranging from 21.6 ± 0.27 mm to 26.3 ± 0.23 while the Gram negative organisms (Pseudomonas fluorescens ATCC 13883, Pseudomonas fragi ATCC 4973, Escherichia coli ATCC 12806, Salmonella enterica subsp. enterica serovar Typhimurium strain ATCC 14028) were less sensitive and resistant to the oil chromatography-mass with inhibition zones ranging from 6.3 ± 0.31 to 9.9 ± 0.21 mm. Out of the tested oil concentrations from 100 – 0.39 mg/mL, MIC obtained for the Gram positive organisms was 1.56 mg/mL while it was 3.13 mg/mL for Gram negative bacteria (except L. monocytogenes). The antifungal test reveals the MIC range of 100 - 0.78 mg/mL in all the fungal isolates tested. African walnut oil has proved to be potentially active against the Gram positive bacterial and fungal species tested indicating that it can be used as a natural alternative to control food spoilage and food poisoning diseases.