Abstract: Objective: To optimize the enzymatic preparation of dietary fiber from Gracilaria waste from agar production. Methods: Crude fiber was obtained from the waste by gradient centrifugation for the removal of filter-aid agents and hydrolyzed by viscozyme; after completion of the hydrolysis, centrifugation was carried out to collect the precipitate as dietary fiber. Crude fiber hydrolysis was optimized using orthogonal array design based on one-factor-at-a-time experiments. Results:  crude fiber was obtained with a recovery of 25.4% after gradient centrifugation at 2500 r/min for 10 min and then at 3500 r/min for 5 min and meanwhile, filter-aid agents were recovered by 60.2%. The optimal conditions for crude fiber hydrolysis were 1:30 material/liquid ratio (g/mL), pH 4.5, 20 FBG/g enzyme dosage, 55 ℃, and 2.5 h. Under these conditions, the yield of dietary fiber was 20.34% (relative to Gracilaria waste based on dry matter). The swelling power and water-holding capacity of the obtained product were 10.25 mL/g and 541.6% respectively. Conclusion: Gradient centrifugation and then viscozyme hydrolysis is feasible for preparing dietary fiber from Gracilaria waste from agar production.

Key words: Gracilaria, residue, dietary fiber