Sodium dodecyl sulfate polyacrylamide gel electrophoresis
(SDS–PAGE) was conducted by using 14% (w/v) polyacrylamide
according to Laemmli [29]. Polypeptide bands of crude extract
(10 lg), commercial bromelain (10 lg), purified bromelain (5 lg)
and standards (5 lg) from BenchMark™ Protein Ladders from Life
Technologies (California, USA) were stained with silver using a
silver staining kit purchased from Bio-Rad laboratories Inc. (Sao
Paulo, Brazil).