Kinetic and thermodynamic characterization of lipase from <i>Aspergillus melleus</i> and its biocatalytic performance for degradation of poly(ɛ‐caprolactone)
Misbah Amin, Haq Nawaz Bhatti, Muhammad Bilal
Abstract
Abstract BACKGROUND Lipases are an interesting class of enzymes that can be used as biocatalysts for poly(ɛ‐caprolactone) degradation. This work reports on the biochemical characterization of a lipase produced through solid‐state fermentation by Aspergillus melleus and its application to degrade poly(ɛ‐caprolactone). RESULTS Lipase demonstrated the best activity and remained stable even after 24 h at an optimal pH of 7.5 and 40 °C. The K m and V max values for p ‐nitrophenyl palmitate hydrolysis derived from Lineweaver–Burk plot were 0.286 mmol L −1 and 142.86 μmol mL −1 min −1 , respectively. Thermal inactivation studies revealed a half‐life of 1732.5 min (28.88 h) at 40 °C, and dramatically reduced at elevated temperatures. The activation energy for substrate hydrolysis was 28.81 kJ mol −1 , whereas the entropy, enthalpy (Δ H °) and free energy (Δ G °) of thermal inactivation of lipase were determined to be 168.73 J mol −1 K −1 , 160.60 and 107.79 kJ mol −1 , respectively, at 40 °C. Increase in temperature showed a decline in Δ G °, but ∆ H * remained constant. Incubation with organic solvents did not influence the enzyme stability; however, urea and guanidine hydrochloride reduced the lipase activity. Under optimal operating conditions, the enzyme presented excellent biocatalytic ability to poly(ɛ‐caprolactone) film degradation, leading to 53% weight loss. Characterization techniques, such as Fourier transform infrared, differential scanning calorimetry and scanning electron microscopy, corroborated the effective biodegradation of poly(ɛ‐caprolactone). CONCLUSION In conclusion, broad working pH, marked stability in the presence of organic solvents, and poly(ɛ‐caprolactone) degradation constitutes a lipase from A. melleus as a promising candidate for large‐scale bioremediation of solid waste.