ABSTRACT

Palm oils extracted from different varieties of Elacis guineensis (dura and te,iera) were examined for their stabilities to microbial deterioration. Twenty six fungi and twenty two bacteria! species were isolated from the oil samples. The isolates were members of the following genera: Penicilliurn, Aspergillus, cladosporiuin, Fusariuni, Saccharoniyces, Muco,; Geotric/zuin, 6'andida for fungi, Pseudomonas, Lactobacillus, Acetobacter, Leuconostoc, Bacillus, Kiebsiella, Staphylococcus, Proteus for bacteria. Amongst the fungi, Aspergillus, Saccharoinyces and Candida species predominated in the dura (Ojukwu) oil while Aspergillus and Saccharoinyccs predominated in the tenera (Qsikwi) oil. For the bacteria, Bacillus predominated in the dura and lenera oil types. Examination of the oil types for growth of microorganisms (fungi and bacteria) revealed that lenera was more stable to bacterial and fungal deterioration while dura was less biostable. At 5% significance level, there was no significant difference between total viable counts (TVC) of microbial numbers and location and samples of oil types. Determination of the biochemical composition of the oil types revealed that crude protein contents of the tich oil samples which ranged from 0.037 to 0.066% were lower than those kept under diHcicnt conditions. A tenera oil sample (8 OS) had the highest free fatty acid (14.76%) while a Jiu'u oil sample (10 OJ) had the lowest (4.46%). The peroxide values (PV) of the fresh oil samples were low (0.00-10.40mEq/kg). The iodine values of the fresh oil samples were lower (23.57-48.95) than those kept under different conditions. Evaluation of the ability of the contaminants to cause deterioration carried out by screen tests showed that all the fungal isolates from lenera oil were capable of growing on and utilizing the oil as sole carbon and energy source while all the fungal isolates from dura oil with the exception of Mucor and Geotrichuni specics grew on and utilized the oil. Also, all the bacteria isolated from tenera with the exception of Acetobacter and Kiebsicila species grew on and utilized the oil while all the bacterial isolates from dura oil except Laclobacillus sp grew on and utilized the oil. Mould growth resulted in an increase with time in mycelial dry weight (g/l OOml) of the cultures in the oil types and subsequent decrease. Microbial growth in the oil types caused decrease in pH and increase in total viable counts (TVC) of thc oils. Gas chromatographic analysis of the extracts of the oil types confirmed that inoculated oil :amk's were subject to microbial utilization of the oil components indicating that spoilage was chemical assimilatory biodeterioration. The difference between dura and lencra is that olcic acid is always present in dura. Oleic acid was produced in lenera only when the mixed culture o[ bacteria (Lactobacillus and Bacillus) was utilizing the oil. This may account for the differences in biostabilities between dura and tenera.