Comparative Preservative Potential of Essential Oils of Ocimum gratissimum from Bambili of the North West and Mbonge of the South West Regions of Cameroon on Scomber scombrus

Essential oils serve as a natural alternative to chemical or synthetic antimicrobials and antioxidants to fight against food borne pathogens or spoilage organisms, inhibiting lipid peroxidation and extending the shelf life of fish and other seafood. This study examines the antibacterial properties of essential oils from leaves of Ocimum gratissimum L. from two localities of the North West and South West of Cameroon on some pathogenic spoilage gram negative and positive bacteria isolated from mackerel, and their antimicrobial and antioxidant effectiveness on the fish quality during preservation for one month at -18oC. The plant materials were harvested from Bambili, the North West Region of Cameroon and from Mbonge, the South West Region of Cameroon and the essential oils extracted by hydro-distillation using Clevenger-type apparatus. Escherichia coli, Salmonella typhi and Staphylococcus aereus were isolated from mackerel by culture techniques and their susceptibility to the essential oils determined by well diffusion method. Psychrophilic bacteria and Enterobacteraceae counts were used to evaluate the microbiological quality of the fish during storage. Total volatile basic nitrogen and thiobarbituric acid reactive substance assays were used as indices to assess the biochemical quality of the fish during storage. Antibacterial susceptibility test showed that essential oils of O. gratissimum from the North West and South West Regions were active on all the tested microorganisms with different degree.The inhibitory diameters for essential oil from the South West Region were 28.0 mm, 27.2 mm and 26.0 mm while that for essential oil from the Bambili were 24.1 mm, 20.4mm and 21.9 mm for Staphylococcus aereus, Escherichia coli and Salmonella typhi respectively. At the end of storage periods, the values of Psychrotrophs plate counts, total volatile base nitrogen and thiobarbituric acid reactive substances for fish samples treated with essential oil from the Mbonge were 2.71log10cfu/g, 12.88 mgN/100g and 0.88 mgMDA/Kg, while that treated with North West essential oil were 3.00 log10cfu/g, 16.24 mgN/100g and 1.26 mgMDA/Kg respectively. From the obtained results, essential oil of O. gratissimum from the Mbonge was the most effective in preserving Atlantic mackerel.