LIPOLYTIC ACTIVITY OF MICROORGANISMS ISOLATED FROM DEGRADING GROUNDNUT AND SOYA OILS

Abstract

The lipolytic activity of microorganisms isolated from degrading groundnut oil and soya oil were investigated. The physicochemical properties of the oils were also determined. Groundnut oil and soya oil were extracted from the seeds with soxhlet extractor using n-hexane as the solvent. The oils were allowed to biodegrade by storing them at temperature of 300C ± 2 for period of eleven weeks. The microorganisms associated with the degrading oils were isolated and identified using standard microbiological and biochemical test after which they were screened for lipase activity and the best lipolytic microorganisms were selected for lipase assay using standard assay technique and Spectrophotometer. The fungi isolated from the oil samples were A. saprophyticus, A. niger, A. fumigatus, A. flavus, Trichoderma viridae, Varicosporium elodea, Penicillium chrysogenum and Articulospora inflatae while the bacteria isolated were, Micrococcus luteus, Streptococcus spp and Staphylococcus aureus. There was an increase in the bacteria load in the oil samples within the first five weeks of storage from 1.0 x 105 to 7 x 105 cfu/ml in groundnut oil while the range of increase in soya oil sample was from 0.1 x 105 to 3.8 x 105cfu/ml. There was an increase in the fungal load throughout the period of degradation with soya oil having the range of 2 x 105 to14 x 105spore/ml and groundnut oil ranged from 1 x 105 to 14 x 105spore/ml. The physicochemical properties of the degrading oils revealed significant increase (𝑝≤0.05) in the Acid value, Free Fatty Acid value, Saponification value, the Peroxide value and Unsaponifiable matter. However the Iodine value of the degrading oils decreased significantly (𝑝≥ 0.05) with increase in the storage weeks. There was no significant changes in the Refractive Index and Specific Gravity of the degrading oils. Staphylococcus aureus and Aspergillus flavus isolated from soya oil and Staphylococcus aureus and Aspergillus fumigatus isolated from groundnut oil were selected for lipase assay based on the zone of clearance. The result of the lipolytic activity revealed that all themicroorganisms selected were able to produce lipase with Aspergillus spp producing more lipase than Staphylococcus aureus. Four lipase producing microorganisms namely Staphylococcus aureus and Aspergillus flavus can be used in the biodegradation of soya oil while Staphylococcus aureus and Aspergillus fumigatus can be used in the biodegradation of groundnut oil and in the production of cost effective lipase for industrial purposes.