Enzymatic hydrolysis of commercial citrus pectin and orange peels by Pectinex Ultra SP-L: best parameter fitting and comparison of results

This work is aimed at determining and comparing the best-fitted kinetic parameters in enzymatic conversion rate of commercial-grade and orange waste (OPW) pectin to galacturonic acid. The Michaelis-Menten approach was adopted. After implementing a suitable experimental plan, the elaboration of the results provided the kinetic parameters by means of the three classical linearization methods, i.e., Lineweaver-Burk, Langmuir and Eadie-Hofstee. However, the best fitting was given by a Matlab-based, non-linear regression method employing the Gauss-Newton algorithm. The product inhibition mechanism proved to be of the competitive type. The kinetic parameters are rmax=1.10 g/(L min), Km=10.42 g/L and KIGA=10.05 g/L for commercial pectin; rmax=0.28 g/(L min), Km=19.28 g/L and KIGA=6.96 g/L for OPW. Accordingly, the hydrolysis rate of the OPW is slower than commercial pectin, but still acceptably fast and convenient.