Experimental procedures
An enzymatic hydrolysis experiment using EMR for producing oligodextran
was conducted to validate the established model. The detailed
experimental procedures have been described in our previous study10 and a brief description is provided here. A piece
of PES20 membrane was placed in a 50 ml dead-end stirred cell (Amicon
8050, Millipore, U.S.A) with an effective membrane surface area of 14
cm2. A constant pressure mode was achieved by filling
the cell with nitrogen gas. A mixture of 0.05 g/L dextranase and 50 g/L
dextran substrate was added to the cell. DI water was continuously added
to the cell to maintain the feed volume constant of 50 ml for an
operation duration of 120 min at different agitation speeds and
operating pressure. The permeate flux was measured every 30 min. The
permeate samples were heated in boiling water for 1 min and then stored
at 4 °C for further analysis.
The total dextran concentration in the permeate was measured using the
phenol-sulfuric acid method. All samples were diluted 500 times with DI
water. Next, a mixture of 2 ml diluted sample, 5 ml of sulfuric acid,
and 1 ml of 6% (v/v) phenol was added to a glass tube. The mixture was
shaken for 1 min and then allowed to stand for 30 min. The sample was
tested at an absorbance of 490 nm in a UV-2100 Spectrophotometer to
determine the dextran concentration. Glucose solutions with
concentrations in the range of 0.01 g/L - 0.07 g/L were used for
calibration.