The effect of cyclodextrins (CDs) on o-diphenol oxidation catalyzed by bana
na polyphenol oxidase (PPO) was studied. The oxidation of dopamine, the nat
ural substrate of banana, in the presence of cyclodextrins was unaffected,
because this hydrophilic phenol does not form inclusion complexes with CDs.
However, when a hydrophobic phenol such as tert-butylcatechol (TBC) was us
ed, a marked inhibition was observed with beta-, hydroxypropyl-beta-, and m
altosyl-beta- CDs. This inhibition was due to the complexation of TBC in th
e CD core, demonstrating that banana pulp PPO worked only toward free subst
rate and not toward the complex TBC-CDs. In addition, the effect of some in
hibitors in the presence of CDs and dopamine as substrate was studied. Incr
easing concentrations of CDs, in the presence of two inhibitors (4-iodophen
ol and cinnamic acid) were able to activate the inhibited enzyme to reach t
he noninhibited level by complexing the inhibitors in the hydrophobic core
of the CDs. This dual effect of CDs as activator and inhibitor was tested i
n crude banana pulp extracts, with surprising activation effects never befo
re described being observed.