Lipase mediated degradation of various polyesters

Abstract

The present research project was aimed to produce microbial lipases, conduct their partial purification, characterization and their prospective use for polyesters degradation. Penicillium fellutanum and Aspergillus melleus were used as lipase producing fungal strains and canola seed oil cake as best substrate for the production of lipases using solid state fermentation. First of all, important parameters were optimized classically for lipase production. Results exposed that the optimum conditions for lipase synthesis by P. fellutanum were incubation period 48 h, moisture contents 50 %, pH 4, temperature 30 ºC and olive oil 2 % while by A. melleus, 96 h incubation period, 60 % moisture level, pH 4, 30 ºC temperature and 3 % olive oil were optimal values. Addition of different nutritional sources significantly affected lipase production. Response surface methodology was also employed for lipase production and an overall 2.05 and 1.92-fold increase in lipase production by P. fellutanum and A. melleus respectively, was being achieved. Crude lipase extract from both fungal strains was subjected to partial purification and, 2.06 and 3.84 folds of purification were obtained after dialysis of P. fellutanum and A. melleus lipase extracts respectively. The partially purified lipase by both fungal strains was characterized by means of optimum pH, temperature, thermal stability etc. Results showed that P. fellutanum lipase was alkaline and A. melleus lipase was neutral in nature. Both fungal lipases showed moderate stability at elevated temperature. Km and Vmax were estimated to be 0.75 mM & 83.33 µmol/min for P. fellutanum lipase while 0.29 mM & 142.86 µmol/min for A. melleus lipase respectively. The activity of lipases produced in this study was evaluated for degradation of five different polyesters. Both the enzymes showed good degradation abilities. Optimization of important parameters for biodegradation like incubation time, enzyme concentration, pH and temperature was carried out. Different analytical techniques like FT-IR, DSC and SEM were applied for the characterization of biodegradation process. FTIR spectra of PVAc, PV-200 and PCL depicted significant decrease in ester functional group and many other transformations at different regions after degradation which was the evidence of their significant weight losses during biodegradation. DSC thermogram data revealed the noticeable reduction in Tg and Tm of PVAc, PV-200 and PCL which confirmed the results. SEM exposed the presence of extensive cracks on the surface after 4 weeks of incubation with both microbial enzymes. The whole study proved that lipases produced in this study could be utilized for the degradation of polyesters for solid waste management.