Comparison of the Biochemical Composition and Nutritional Quality Between Diploid and Triploid Hong Kong Oysters, Crassostrea hongkongensis

Comparison of the Biochemical Composition and Nutritional Quality Between Diploid and Triploid Hong Kong Oysters, Crassostrea hongkongensis

This study is the first systematic comparison of the biochemical composition and nutritional quality between diploid and triploid Hong Kong oysters, Crassostrea hongkongensis. Results showed that in the reproductive season, the glycogen content in five tissues (gill, mantle, adductor muscle, labial palps and gonad) was significantly higher (P < 0.05) in triploids than in diploids, with odds ratios (ORs) of 96.26, 60.17, 72.59, 53.56, and 128.52%, respectively. In the non-reproductive phase, significant differences in glycogen content (P < 0.05) between diploid and triploid oysters existed only in gill and gonad. In both diploid and triploid Hong Kong oysters, quantitative real-time PCR analysis of the glycogen synthesis gene (ChGS) and glycogen phosphorylase gene (ChGP) showed that the gene expression patterns matched the pattern of variation in glycogen content. Moreover, in both the reproductive and the non-reproductive phases, triploid Hong Kong oysters had a well balance of essential amino acids and were thus a well source of high-quality protein. Surprisingly, in both phases, significantly higher (P < 0.05) percentages of four essential fatty acids (a-linolenic acid, linoleic acid, eicosapentaenoic acid, and docosahexaenoic acid) were observed in triploids than in diploids. Additionally, the ratio of n-3/n-6 polyunsaturated fatty acids (PUFAs) was much higher in triploids than that in diploids. Variations in Biochemical composition were consistent with the relative expression of the citrate synthase gene (ChCS) and the a-ketoglutarate dehydrogenase gene (ChKD), which are key enzyme genes of the tricarboxylic acid cycle. Overall, the triploid Hong Kong oyster has a better nutritional value and taste than the diploid in terms of glycogen content, protein quality and fatty acid content.

本研究首次对香港牡蛎（Crassostrea hongkongensis）二倍体和三倍体之间的生化成分和营养质量进行了系统比较。结果表明，在繁殖季节，三倍体牡蛎五个组织（鳃、外套膜、闭壳肌、唇瓣和性腺）中的糖原含量显著高于二倍体（P < 0.05），优势比（ORs）分别为96.26%、60.17%、72.59%、53.56%和128.52%。在非繁殖期，二倍体和三倍体牡蛎之间的糖原含量仅在鳃和性腺中存在显著差异（P < 0.05）。在香港牡蛎二倍体和三倍体中，对糖原合成基因（ChGS）和糖原磷酸化酶基因（ChGP）进行的实时定量PCR分析表明，基因表达模式与糖原含量的变化模式相符。此外，在繁殖期和非繁殖期，三倍体香港牡蛎的必需氨基酸平衡良好，是优质蛋白质的良好来源。令人惊讶的是，在这两个时期，三倍体中四种必需脂肪酸（α -亚麻酸、亚油酸、二十碳五烯酸和二十二碳六烯酸）的百分比均显著高于二倍体（P < 0.05）。此外，三倍体中n - 3/n - 6多不饱和脂肪酸（PUFAs）的比例远高于二倍体。生化成分的变化与柠檬酸合酶基因（ChCS）和α -酮戊二酸脱氢酶基因（ChKD）的相对表达一致，这两个基因是三羧酸循环的关键酶基因。总体而言，就糖原含量、蛋白质质量和脂肪酸含量而言，三倍体香港牡蛎比二倍体具有更好的营养价值和口感。