Abstract: Objective: To compare the antioxidant activity of different protein fractions from Chirocephalus diaphanous and optimize the extraction of the fraction with the strongest antioxidant activity. Methods: The residue left after water-soluble protein extraction of Chirocephalus diaphanous was extracted with 0.1 mol/L aqueous NaOH solution, 0.1 mol/L aqueous acetic acid solution and 95% ethanol, respectively. The antioxidant activity of the water-soluble, acid-soluble protein, alkaline-soluble protein and alcohol-soluble proteins obtained was comparatively assessed based on their DPPH, hydroxyl and superoxide anion radical activities and total reducing power to identify the protein fraction with the most powerful antioxidant activity among them. Moreover, response surface methodology based on central composite design was used to optimize the extraction of the most antioxidant protein fraction from Chirocephalus diaphanous. Results: The contents of water-soluble, alkaline-soluble, alcohol-soluble and acid-soluble proteins were 25.03%, 26.98%, 1.83% and 0.53%, respectively. Water-soluble protein from Chirocephalus diaphanous had stronger antioxidant activity than other three proteins. The best results for the extraction of eater-soluble protein from Chirocephalus diaphanous were achieved after 2.8 h extraction at 49.8 ℃ and a material-to-liquid ratio of 1:7.5. The error between the predicted and experimental extraction yields was 0.88%. Conclusions: Water-soluble protein has the highest antioxidant activity and its optimal extraction process is feasible.

Key words: Chirocephalus diaphanous, protein, sequential extraction, antioxidant activity, process optimization