DPPH is a relatively stable free radical that has been widely
used to evaluate antioxidant properties of proteins and their
hydrolydates.
Although relatively high DPPH scavenging activity was observed
in the first 30 min with salmon and trevally
fish proteins and their hydrolysates, NaCas
and hydrolysates had limited activity within 30 min, and were
therefore tested for up to 24 h (Fig. 3).The higher DPPH scavenging
activity was observed at a longer incubation time. The results suggest
caseins and their hydrolsyates have limited electron-donating
capacity. Most hydrolysates showed higher DPPH scavenging
activity than NaCas. Overall, the DPPH scavenging activity of papain
treatments was independent on the hydrolysis time and
was higher than the other two groups. Conversely, the DPPH
scavenging activity of pancreatin- and trypsin-treatments was
dependent on the hydrolysis time and was higher than that of
NaCas only after hydrolysis for a sufficiently long time (>1 h for
pancreatin and >4 h for trypsin treatments). The different scavenging
activity of papain hydrolysates may be a result of its higher
enzymatic activity, but less specificity in hydrolysing NaCas, producing
low MW peptides without defined amino acid sequences.