Lipid composition of fresh and frozen-stored krill.

Lipid classes in seven krill (Euphausia superba D.) samples, fresh and after various periods of storage at 251 K were compared. Fresh krill lipid composition differed from that determined in frozen samples, depending on storage duration, season of harvest, and developmental stage (as determined on a few samples only). Phospholipids proved most susceptible to changes, as opposed to triglycerides, which were most resistant; diglycerides and cholesterol esters were also destroyed. The freezing process per se affected the lipid composition only slightly; however, after 30 days storage the amount of free fatty acids almost doubled. After 6 months storage at 251 K, 70% of phospholipids were decomposed and the amount of free fatty acids increased by a factor of 6 to 20. Monoglycerides, absent from fresh krill, appeared after several months of frozen storage. Juvenile krill were more susceptible to lipolytic changes. Females bearing mature eggs contained stable phospholipids; it was only triglycerides that were hydrolysed. It seems probable that discrepancies encountered in the literature data on krill lipid composition are the result of frozen krill being analysed.