| Oysters are commercially important shellfish, providing abundant and high-quality animal protein in China. Currently the aquaculture oysters are all Crassostrea species and little is known about the dietary property and resource quantity of Hyotissa oysters, not to mention the breeding and aquaculture technologies. Locally named stone oysters, Hyotissa oysters are actually quite popular in Weizhou Island, Guangxi, and different from Crassostrea species, the adductor muscles are main edible parts in Hyotissa oysters. The stone oysters include three species, i.e. H. hyotis, H. inaequivalvis, and H. sinensis. The nutritional composition of the adductor muscles of H. hyotis from South Korea has been analyzed, but the nutritional composition and quality of the stone oysters in China has never been researched. To compensate for this, in this study, we collected wild stone oysters around Weizhou Island in Guangxi in Aug. 2024 and detected the nutritional compositions in the edible adductor muscles according to the national standards of China, i.e. GB 5009.3, GB 5009.4, GB 5009.5, GB 5009.6, GB 5009.124, GB 5009.158, and GB/T 9695.31. The qualities of amino acids and fatty acids were assessed by the evaluation indices such as the amino acid score, the chemical score, the essential amino acid index, the taste activity value, the atherogenicity index, and the thrombogenicity index using their composition and contents. Results showed that: 1) the contents of total ash, fat, and total sugar in the adductor muscles of the three Hyotissa oysters were comparable, ranging from 2.16~2.43 g/100g, 1.28~1.42 g/100g, and 2.24~2.69 g/100g, respective, while the protein contents were 13.68~16.99 g/100g; 2) 17 amino acids were identified in the adductor muscles of all the three Hyotissa oysters, including 7 essential amino acids, 4 semi-essential amino acids, and 6 non-essential amino acids; the contents of the amino acids in three stone oysters were similar, only that the contents of cysteine and valine in H. hyotis were significantly lower than that in H. sinensis, and the tyrosine in H. hyotis were significantly higher than that in H. inaequivalvis; in all the three species, the glutamic acid had the largest content (2.10~2.40 g/100g), followed by the aspartic acid (1.30~1.45 g/100g); the cysteine had the least content of only 0.03~0.05 g/100g; H. hyotis had the highest contents of three flavor amino acids, i.e. aspartic acid, glutamic acid, and alanine, the total amino acid content, essential amino acid content, non-essential amino acid content, semi-essential amino acid content, and flavor amino acid content are highest in H. hyotis but comparable in three stone oysters; the essential amino acid content to total amino acid content was almost 40%, and the essential amino acid content to non-essential amino acid was over 70% for each species; 3) the compositions of fatty acids identified in three oysters were quite different that H. hyotis had 15 fatty acids including 5 saturated fatty acids, 3 monounsaturated fatty acids, and 7 polyunsaturated fatty acids while H. inaequivalvis and H. sinensis had only 12; the total fatty acids in H. hyotis was the highest (0.414 g/100g), while that in H. inaequivalvis was the least (0.356 g/100g); C16:0 had the highest content among these fatty acids followed by C18:0; both C20:2 and C20:3n3 were over quantitative limit only in H. hyotis; 4) the lysine had the largest amino acid score and chemical score and the first limiting amino acid was methionine+ cysteine; lysine in H. hyotis, leucine and lysine in H. inaequivalvis, and 6 amino acids in H. sinensis reached the FAO/WHO standards; the aspartic acid had the highest taste activity value (13.0~14.5) than other amino acids followed by the glutamic acid; 5) the contents of EPA, DHA, total monounsaturated fatty acids, total polyunsaturated fatty acids were highest in H. hyotis, while the DHA/EPA was the highest in H. inaequivalvis (2.081) but lowest in H. sinensis (1.590); the content of EPA+DHA in the stone oysters was 18~33 mg/100g; the index of atherogenicity was the highest in H. hyotis and the lowest in H. inaequivalvis, and the index of thrombogenicity for the three stone oysters was 0.037~0.068, far lower that scallop and fish. Our study suggested that all the three stone oysters were products with high proteins and low fatties and the adductor muscles were superior marine animal protein. H. sinensis had more balanced amino acid contents, while H. hyotis had the most and balanced fatty acid species and health effects but all three species had high saturated fatty acid contents which had good effects on thrombogenicity prevention. This study firstly researched the composition and quality of the adductor muscles of the stone oysters. Our results would be a good reference for the development and utilization of the Hyotissa germplasms in Weizhou Island. |
