Preliminary chemical and nutritional characterization of liver from longnose skates (Raja rhina)

Skates (Raja rhina) have recently become a small commercial fishery in Alaska and along the western United States coast. Most of the skate byproduct is discarded or made into meal; therefore, there is opportunity to enhance the utilization for skate byproducts. The objective of this research project was to chemically characterize longnose skate livers. Livers from five long nose skates, caught off the coast of Kodiak, Alaska, were obtained immediately after the fins (called “wings”) had been removed by a commercial processor. Each liver was subjected to the following analysis: proximate composition, minerals, amino acids, α-tocopherol, protein gel electrophoresis, fatty acid profiles, thiobarbituric acid reactive substances (TBARS) and biogenic amines (BA). Livers were composed of lipid (49.6%), moisture (41.0%), protein (10.9%) and ash (0.8%). High levels of α-tocopherol were found in the livers (142 μg/g oil). Fatty acid profile indicated that the lipids extracted from livers contained high concentrations of eicosapentaenoic acid (16.0%) and docosahexaenoic acid (17.7%). Average TBARS values were low at 1.5 μg malondialdehyde/g oil, indicating low levels of lipid oxidation. The lysine content as percent of total amino acids on a weight basis was 6.1% and methionine content was 2.8%. Analysis of BA found putrescine (31 mg/kg liver) and spermine (85 mg/kg liver) present. Preliminary results suggest long nose skate livers as an abundant source of n-3 fatty acids and amino acids.