The objectives of the present study were to examine the antioxidant activity of fractions with different isoelectric points from salmon enzymatic hydrolysates and obtain peptide fractions of sufficient amounts with higher antioxidant peptide fraction, which could be applied to the food and animal model systems. The salmon enzymatic hydrolysates were fractionated on the basis of the amphoteric nature of sample peptides by preparative isoelectric focusing without toxic solvents and reagents, which is termed autofocusing. Acidic and basic fractions showed higher 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity than the other fractions. The basic fractions showed higher hydroxyl (OH) radical scavenging activity. The weak acidic and weak basic fractions showed higher oxygen radical absorbance capacity (ORAC) values than the acidic and basic fractions. The acidic fraction showed higher metal chelating activity than other fractions. The acidic fraction suppressed lipid oxidation in the cooked patties to a greater extent than other fractions. These results suggest that peptides fractions from salmon enzymatic hydrolysate are effective antioxidant, and that autofocusing could be useful to increase antioxidant activity for application to food and animal model systems.

Some bioactive peptides have been identified by activity-guided fractionation. However, it is difficult to prepare or synthesize enough amounts of active peptides for food ingredients and for animal or human trials. The objective of the present study was to prepare peptide fractions of sufficient amounts with high antioxidant activity which could be applied to the food and animal model. Oyster hydrolysate was fractionated the basis of the amphoteric nature of sample peptides by preparative isoelectric focusing (autofocusing). To monitor the fractionation of peptides by autofocusing, amino acid analysis of the autofocusing fractions was performed. Each autofocusing fraction was evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl (OH) radical scavenging activities, oxygen radical absorbance capacity (ORAC), and Fe 2+ chelatingassays. More than 40% of the peptides were distributed between Fr. 4 and 7 (pH<5.0). Approximately 16% of the peptides were recovered in basic fractions (pH>10.0; Fr. 9-10). 11 % of peptides were recovered in the neutral fraction (6.0<pH<7.0; Fr. 8). The peptides in the acidic and basic fractions are characterized by a higher content of acidic and basic amino acids, respectively. Acidic fraction showed higher ORAC values than crude oyster hydrolysate. Also, the acidic fraction showed high DPPH and OH radical scavenging activity. On the other hand, basic fraction showed higher chelating ability than crude oyster hydrolysate. In the present study, oyster peptide fractions of large-scale with high antioxidant activity were successfully fractionated by autofocusing for food additives and animal trials.