Antioxidant Activity of Protein Isolate Obtained by the pH Shift Technique from Hydrolyzed and Unhydrolyzed Shrimp Processing Discards

Protein isolates from hydrolyzed and unhydrolyzed shrimp waste were prepared using
the pH shift method. The conditions for protein isolation from unhydrolyzed shrimp
waste by the pH shift method were standardized with respect to waste to distilled water
ratio (1:2.5, 1:5, 1:7.5, and 1:10 w/v) and the alkaline pH (9.0, 10.0, and 11.0) to which
the waste was to be adjusted before protein precipitation for higher yield of protein isolate.
The yield of precipitate with waste to distilled water ratio of 1:2.5 (17.3 ± 0.9)
was lower (p < 0.05) compared to the other three dilutions. The pH to which the waste
is adjusted before precipitating the proteins at pH 4.5 had no effect (p > 0.05) on the
yield. The antioxidant activity of the protein isolate obtained by the pH shift method
from unhydrolyzed waste was compared with that obtained from the waste hydrolyzed
with Alcalase®. The DPPH scavenging activity of protein isolate after enzyme hydrolysis
was significantly higher than that of protein isolate from unhydrolyzed waste. With
respect to recovery of total antioxidant activity, protein isolation from unhydrolyzed
waste was superior to hydrolyzed waste due to higher yield