Quality characteristics of green sea urchin (Strongylocentrotus droebachiensis) gonads as affected by the season and dietary factors

Liyanapathirana, Chandrika M. (2001) Quality characteristics of green sea urchin (Strongylocentrotus droebachiensis) gonads as affected by the season and dietary factors. Masters thesis, Memorial University of Newfoundland.

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Abstract

The eating quality of sea urchin gonads from Strongyiocentrotus droebachiensis harvested in the Newfoundland coasts as affected by the season and an artificial diet was assessed. Evaluations were performed on the basis of biochemical and fatty acid composition, total and free amino acid contents, and contents of nucleicacids and pigments, among others. -- Noticeable changes occurred in the biochemical composition of wild and cultured sea urchin gonads. Moisture and lipid contents showed an inverse relationship in all samples examined. Sea urchin gonads had the highest amount of lipid and the lowest amount of moisture in the spring. Lipid content of cultured sea urchin gonads decreased with increased feeding time while the moisture content increased. Protein content, on the other hand, was highest in the fall in the wild sea urchins. The corresponding value for cultured sea urchins was observed 9 weeks after feeding on an artificial diet. Relative proportions of lipid and protein were quite low in the wild as well as cultured sea urchin viscera. -- There were no qualitative differences in the lipid class composition between gonads and viscera of wild and cultured sea urchins. Major non-polar lipid classes were triacylgiycerol (TAG), free fatty acids (FFA) and sterol (ST) while major polar lipid classes were phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Triacylgiycerol content was highest in the spring and fall in gonads and viscera, respectively. On the other hand, TAG content in cultured sea urchins was increased with length of feeding period. Phosphatidylcholine was the dominant polar lipid class in wild sea urchin tissues. However, PE became dominant in cultured urchins on week 9 after feeding on an artificial diet. -- The fatty acids 14:0 and 16:0 were the major saturated fatty acids (SFA) consistently present in total, polar and non-polar lipids of sea urchin gonads and viscera irrespective of their origin while 20:4n-6 and 20:5n-3 were the major polyunsaturated fatty acids (PUFA). However, in cultured sea urchins 18:2n-6 became dominant with increasing feeding period with a concurrent decrease in the content of 20:1n-3. The fatty acid 20:In-15 was the dominant monounsaturated fatty acid (MUFA) in wild sea urchin tissues. The content of PUFA increased during cold climatic conditions with a simultaneous decrease in the content of SFA. These changes were reversed during warm seasons. In cultured sea urchins PUFA content increased with increasing feeding period with a concurrent decrease in SFA content. -- Glycine was the dominant amino acid in the total amino acids (TAA) of wild sea urchin gonads and viscera. On the contrary, TAA of cultured sea urchin gonads was dominated by tyrosine on week 9 after feeding on the artificial diet. However, there were no qualitative differences in the TAA between wild sea urchins and their cultured counterparts. Glycine was also the dominant amino acid in the free amino acid (FAA) profiles of both wild and cultured sea urchins. The relative content of glycine was highest in the spring in both gonads and viscera of wild sea urchins. This was reduced considerably with increased feeding period in cultured sea urchins. There was a marked increase in the total FAA content of cultured sea urchin gonads and viscera. Furthermore, the content of deoxyribonucleic acid (DNA) was higher than that of ribonucleic acid (RNA) in wild as well as cultured sea urchin tissues. -- Total carotenoid content was highest in the spring in the gonads of wild sea urchins. However, this was reduced to a minimum in the viscera in the spring. Further, total carotenoid content was decreased in cultured sea urchin gonads and viscera with increased feeding period. Major carotenoids were echininone and fucoxanthin in gonads and viscera, respectively, irrespective of their origin. The relative proportion of echininone was highest in the spring and was lowest in the summer in the wild sea urchin gonads. In addition, (J-carotene was present in all samples examined. In wild sea urchin gonads a maximum amount of (3-carotene was detected in the summer. In cultured urchins the relative proportion of echininone increased with length of feeding period with a simultaneous reduction in (3-carotene levels. -- The study reported here thus demonstrates the importance of seasonal variations and feed supply on the quality characteristics of sea urchins. A number of biochemical indices will be examined to ascertain the eating quality of sea urchin aonads.

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