Enzymatic Hydrolysis of Xylan from Coffee Parchment in Membrane Bioreactors

Xylooligosaccharides (XOs) production from xylan, extracted from coffee parchment, using two stirred tank reactors (STRs) and two membrane bioreactors (MBRs) was studied for the first time. In the reactors, xylanase either free in a solution (E-STR, E-MBR) or covalently immobilized on magnetic nanopartides (MNP-STR, MNP-MBR) was used. A continuous production of reducing sugars in both MBRs was obtained. In the E-MBR, the same conversion of E-STR at a low substrate concentration (1 mg mL(-1)) (97%) was obtained. At higher substrate concentration, the conversion increases by a quarter in E-MBR on increasing the residence time and doubles in MNP-MBR by increasing the amount of immobilized enzyme. The unchanged apparent K-M (about 8 mg mL(-1)) showed that the affinity of the enzyme for the substrate was not altered by the immobilization process. In E-MBR, the enzyme/substrate affinity is even improved (K-M: 2.58 mg mL(-1)), thanks to the continuous removal of the inhibition products, present in the initial xylan solution, by the membrane process.