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North Pacific krill is widely distributed in the waters around Japan, however its utilization for human consumption has been limited due to its small size. We have investigated the proximate composition, the amino acid, free fatty acid, mineral and protein composition, respectively, as well as the residual proteolytic activity of krill protein, as recovered by acidic- and alkaline-aided isoelectric solubilization/precipitation, in order to facilitate effective utilization of this krill species. Krill protein yield was 31.7 and 73.4 % by acidic and alkaline treatment, respectively. Both treatments resulted in a comparable higher content of essential amino acids than that in whole krill, accompanied with effective removal of insoluble materials. Three major proteolytic active bands with molecular weights of approximately 28, 18 and 16 kDa, as estimated by gelatin-based zymography, were detected. Pronounced residual proteolytic activity was observed in the krill protein after alkaline processing, implying the possible involvement of proteinase(s) in protein degradation during alkaline solubilization. Based on these results, we suggest that inhibition of proteolysis during isoelectric solubilization/precipitation is required for the effective use of North Pacific krill. [ABSTRACT FROM AUTHOR]