Ethanol can alter the secondary, tertiary or quaternary structure
of enzymes, distorting the binding sites of amino acid residues arranged
along their catalytic site. The fluorescence of the purified,
cryoprotected bromelain remained unaltered after freeze-drying
(Fig. 3A). Bromelain contains five tryptophan residues [42] and
extensive sequence homology with papain, which suggests that
three of the residues are buried in the hydrophobic core whereas
two may be located near the surface of the molecule [43,44]. The
maximum peak of purified, cryoprotected bromelain at pH 7.0
was recorded at 345 nm, similar to commercial bromelain (349
nm), showing the integrity of the hydrophobic centers of the bromelain
after ethanol precipitation.