Abstract:

Papain hydrolyzate of silkworm pupae protein with DPPH radical scavenging activity was decolorized by the
combined use of activated clay, alkaline Ca-bentonite and bentonite. Based on decolorization efficiency and retention rate of
radical scavenging activity, the decolorization conditions were optimized by using single-factor design and central composite
design (CCD) coupled with response surface methodology (RSM). When the hydrolyzate with a concentration of 9.61 mg/mL
and an initial pH of 7.2 was added with activated clay:alkaline Ca-bentonite:bentonite (1:1:1) in a proportion of 1.9% and
incubated for 1.0 h in a thermostatically controlled water at 60 ℃ with shaking at a speed of 150 r/min, it retained 84.5%
of its original DPPH radical scavenging activity and the decolorization rate was 94.5%, both close to the predicted values
with a relative error less than 5%, suggesting the reliability of the developed response surface model. Comparing the amino
acid composition of the decolorized hydrolyzate with that of the untreated one, it was found that the contents of
hydrophobic and aromatic amino acids which are significantly effective in inhibiting DPPH free radical were reduced
after the decolorization treatment.

Key words: silkworm pupae protein, DPPH radical scavenging rate, decolorization, response surface methodology