Abstract: The enzymatic deproteinization of polysaccharides from cuttlefish muscle (Sepia lycidas) was optimized using an orthogonal array design. Trypsin was determined to be the optimal enzyme to hydrolyze the protein in the crude polysaccharide extract. Enzyme dosage, hydrolysis temperature, pH and hydrolysis time were selected as independent variables for optimization, and the response variables were deproteinization efficiency and polysaccharide loss. The enzymatic method was compared with trichloroacetic acid (TCA) and isoelectric point (IP) methods. Meanwhile, the free radical scavenging capacity of the deproteinated polysaccharides was also studied. The results showed that the optimum deproteinization conditions were obtained as follows: trypsin dosage, 3.0 g/100 mL; hydrolysis temperature, 53 ℃; pH, 8.2; and hydrolysis time, 1.5 h, yielding a deproteinization rate as high as 89.43% and a polysaccharide loss of only 1.78%. In terms of both dependent variables, the enzymatic method was better than TCA and IP methods. The percentage scavenging of hydroxyl radical by the deproteinated polysaccharides obtained by the enzymatic, TCA and IP methods were 45.72%, 38.72% and 25.18%, with IC50 values of 12.44, 16.37 and 34.64 mg/mL, respectively, and the percentage scavenging of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical by these purified polysaccharides were 68.00%, 30.08% and 23.10%, with IC50 values of 7.62, 16.71 and 28.96 mg/mL, respectively. The free radical scavenging activities of the deproteinated polysaccharides from S. lycidas muscle were ranked as follows: enzymatic method > TCA method > IP method.

Key words: Sepia lycidas, polysaccharides, enzymatic method, deproteinization, free radicals