Abstract:
Lipases (triacylglycerol acylhydrolases, EC 3.1.1.3) are group of enzymes that catalyze the hydrolysis and the synthesis of esters from glycerol and long- chain fatty acids. Microbial lipases are among the enzymes that have gained great interests in terms of research in recent years due to their potential applications in industries. Management of waste and turning waste to wealth are attracting the researchers in order to meet input demand of bioprocess industries. Nineteen fungal isolates were isolated from palm oil mill effluent (POME), soil from POME dump sites and rotten palm fruits. The isolates were screened qualitatively on Tween 80 agar plates for their lipase producing potentials and ten out of nineteen of them were positive. These strains were selected and identified based on their morphological and physicochemical characteristics and were further screened quantitatively in POME–based medium (submerged fermentation). The most promising yeast strain, candida species PF7 with the activity of 2.223 U/ml at 72 hrs and the most potent mould strain, Aspergillus species designated PMS3 producing 2.445 U/ml of lipase at 96 hrs were selected. Cultural conditions were optimized in order to improve their lipolytic potentials. The supplementation of the two organic nitrogen sources (peptone and yeast extracts) each at 0.5% concentration and 0.5% olive oil to undiluted POME at pH 4.0 greatly enhanced lipase production with the peak activities of 6.223 U/ml at 72 hrs and 8.557 U/ml at 96 hrs and peak biomass of 6.48 g/l at 120 hrs and 6.74 g/l at 96 hrs by PF7 and PMS3 respectively at 30oC. Subjecting the produced crude PF7 and PMS3 lipases to ammonium sulphate precipitation, Candida species PF7 showed the enzyme activity of 4.563 U/ml in 80% ammonium sulphate while in 60% ammonium sulphate, the enzyme activity by Aspergillus sp PMS3 was 5.554 U/ml. Further purification of the desalted enzymes by gel filtration chromatography using sephadex G-100 showed 7.07 and 5.83 purification folds in PF7 and PMS3 lipases respectively. The two lipases showed maximum relative activity at pH 8.0 and 40oC. Ca2+, Mn2+ and Mg2+ stimulated the activity of the purified lipases while Fe2+ and Co2+ exhibited inhibitory effect on their activity. Cu2+stimulated the activity of lipase produced by the PMS3 while it has inhibitory effect on lipase activity of PF7. This study demonstrated that POME, an agricultural waste, has a potential of serving as a low cost substrate for economic production of lipase in submerged fermentation.
