PRESERVATIVE POTENTIALS AND ANTIBACTERIAL ACTIVITY OF DACRYODES EDULIS G. DON (AFRICAN PEAR) SEED OIL AGAINST BACTERIA ISOLATED FROM MEAT AND FISH

Abstract

Dacryodes edulis (G. Don) commonly known as ‘African pear‘ have seeds that are enclosed in a seed coat. This study was carried out to determine the preservative effect and antibacterial activity of oil from seed of Dacryodes edulis against pathogenic microorganisms. Fruits of Dacryodes edulis were purchased from the market in Orlu, Imo State. Fresh meat and fish were purchased at different locations in King’s market, Akure, Ondo State. Typed cultures which includes Shigella dysenteriae ATCC 11835, Salmonella typhimurium ATCC 14028, Escherichia coli ATCC 700728 and Klebsiella pneumoniae ATCC® 4352 were sourced from the culture collection of the Federal Institute of Industrial Research (FIIRO), Oshodi, Lagos State. Clinical isolates includes Salmonella typhi, Escherichia coli, Shigella dysenteriae and Klebsiella pneumoniae were obtained from Don Bosco Hospital, Akure, Ondo State. Microorganisms from fresh meat and fish were isolated and identified using conventional methods. Proximate, mineral and phytochemical analyses were carried out using standard methods. Bioactive compounds in the oil was elucidated using Fourier Transform Infrared Spectroscopy (FTIR) and Gas Chromatography Mass Spectrometry (GC-MS). Antimicrobial activity of oil against microorganisms was determined using agar well diffusion technique. Preservative quality of oil on fish and meat was investigated at 4°C and 37°C. Organoleptic properties of preserved fish and meat was determined using ten panelists. The highest bacterial count of was obtained in pork (6.12 x 104 cfu/mL) and mackerel (3.56 x 104 cfu/mL). The bacteria isolated include Bacillus cereus, Enterobacter aerogeness, Escherichia coli, Klebsiella pneumoniae, Lactobacillus plantarum, Leuconostoc mesenteroides, Micrococcus luteus, Proteus vulgaris, Pseudomonas aeruginosa, Serratia marcescens, Staphylococcus aureus and Streptococcus pyogenes. Staphylococcus aureus (31.80% and 27.50%) emerged as the most dominating bacteria. Carbohydrates, fat, protein, crude fibre, moisture and ash contents of the oil were 36.8%, 34.7%, 10.7%, 7.1%, 6.1% and 4.6% respectively. Potassium was the most abundant mineral (106.5 mg/g) compared (p<0.05) to other minerals like phosphorous (102.5 mg/g) and magnesium (64.7 mg/g). Saponin, alkaloids, tannins, flavonoids, steroids, terpenoids and phenol compounds were phytochemicals present in the oil. FTIR and GC-MS confirmed the presence of functional groups like –OH, -CH3, -COOH and various bioactive compounds like oleic acid, 9-12- Octadecanoic acid, Octadecanoic acid, Hexadecanoic acid, Terpin–4–ol, 2-hexenal and others. Zones of inhibition of oil against microorganisms ranged from 10.30 to 26.00 mm at 20 mg/ml. The highest zones (18.30 mm to 26.00 mm) of inhibition were obtained against Bacillus cereus, Staphylococcus aureus, Salmonella typhi and Shigella dysenteriae ATCC 11835. The minimum inhibitory concentrations (MIC) of the oil ranged from 5 to 20 mg/mL and minimum bactericidal concentrations (MBC) was between 10 to 20 mg/mL. Best preservative property of oil was observed on fried fish and meat kept at 4°C with no microbial growth. The highest microbial load (3.95 x 106 cfu/mL) occurred in fresh chicken coated with oil from D. edulis seed after 7 days of preservation. Fish and meat fried with extracted oil were well accepted (9.00) than those fried with groundnut oil (3.50). The antibacterial and preservative qualities of oil on fish and meat confirmed that the oil is good for cooking, without deteriorating for longer period. Oil from D. edulis seed could be of immense benefits to pharmaceutical and food industries towards the development of new antimicrobial and preservative agents.