The reaction rate of starch hydrolysis catalyzed by a glucoamylase covalent
ly bound to chitin particles was measured in a Differential Fixed-Bed React
or (DFBR). Under selected test conditions the initial reaction rate may rep
resent biocatalyst activity. Some aspects which influence measurement of th
e initial reaction rate of an immobilized enzyme were studied: the amount o
f desorbed enzyme and its hydrolytic activity, the extent of pore blockage
of the biocatalyst caused by substrate solution impurities and the internal
and external diffusional mass transfer effects. The results showed that th
e enzyme glucoamylase was firmly bound to the support, as indicated by the
very low amount of desorbed protein found in the recirculating liquid. Alth
ough this protein was very active, its contribution to the overall reaction
rate was negligible. It was observed that the biocatalyst pores were susce
ptible to being blocked by the impurities of the starch solution. This latt
er effect was accumulative, increasing with the number of sequential experi
ments carried out. When the substrate solution was filtered before use, ver
y reliable determinations of immobilized enzyme reaction rates could be per
formed in the DFBR. External and internal diffusional resistences usually p
lay a significant role in fixed-bed reactors. However, for the experimental
system studied, internal mass transfer effects were not significant, and i
t was possible to select an operational condition (recirculation flow rate
value) that minimized the external diffusional limitations.