Oysters (Mollusca, Bivalve), are the most extensively cultured marine shellfish globally (Teng et al., 2022). Renowned for their superb nutritional value and distinctive flavor, they are highly prized by consumers and are often referred to as the “milk of the ocean” (Yuasa et al., 2018). In Europe, there is a well-known adage: “Avoid oysters in months without an ‘R’.” This saying stems from the seasonal nature of diploid oysters’ reproduction. From May to August each year, these oysters spawn, leading to a decrease in meat quality and flavor due to the release of gametes, which can diminish the consumer’s eating experience. To address this issue, the aquaculture industry has begun introducing triploid oysters. These oysters, being sterile, do not undergo gonad development, thus conserving energy that would otherwise be expended during this process. This energy conservation results in enhanced meat quality, offering a promising solution to maintaining year-round oyster consumption without compromising taste (Villanueva-Fonseca et al., 2017; Qin et al., 2018).

In recent years, a significant amount of research has focused on the crossbreeding of oysters, resulting in the production of triploid oysters that exhibit superior traits. These studies have explored both intraspecific and interspecific hybridizations, such as the crossbreeding of C.gigas with diploid oysters and the combination of tetraploid C. gigas with diploid C.ariakensis and C.angulate (Que and Allen, 2002; Jiang et al., 2022; Li et al., 2022a). The resultant triploid offspring display characteristics inherited from both parent strains. Additionally, triploid oysters offer several advantages including rapid growth, larger size, lower mortality rates during the breeding season, and greater meat yield. For instance, triploid oysters grew 88% to 190% faster than their diploid counterparts (Guo et al., 2008). Similarly, the soft tissue weight (TWR) and condition index (CI) were significantly higher in triploid oysters (Park and Choi, 2022). The edible components of oysters typically include the gonadal gland, hepatopancreas, gills, and adductor muscle. Based on our unpublished data, there are notable differences in the proportions of these tissues between different ploidies; for example, the gonadal gland, hepatopancreas, gills, and adductor muscle make up 28.08%, 4.34%, 11.05%, and 10.43% of triploid oysters respectively, compared to 31.94%, 12.98%, 10.29%, and 8.24% in diploids. These variations in tissue structure and nutritional composition are especially pronounced in the gonads. Triploid oysters also show distinct differences in cellular and tissue morphology compared to diploids. For instance, the internal structure of gill filaments, mitochondrial diameter, and muscle fibers are more developed in triploids (Kong et al., 2003; Dong et al., 2023). Studies of the gonads have revealed that triploid oysters possess smaller follicles and more abundant connective tissues, and their gonads do not undergo significant changes during the breeding season, remaining in a state of diapause (Wang et al., 2021). These structural and nutritional differences likely contribute to the varied flavors between triploid and diploid oysters, underscoring the importance of differentiating the taste profiles of various oyster tissues to better understand the underlying causes of flavor discrepancies in oysters of different ploidies.

In the quest to evaluate the quality of oysters varying in ploidy, the triploid Hong Kong oysters exhibit significantly higher levels of glycogen and n-3/n-6 polyunsaturated fatty acids (PUFAs) compared to their diploid counterparts (Qin et al., 2018). Beyond these nutrients, flavor compounds also play an important role in the sensory and quality characteristics of oysters. Fresh oysters have a unique taste and aroma, which greatly influence consumer choices. Therefore, studying the flavor characteristics of oysters is of great significance for the development of the oyster industry. Flavor is a comprehensive concept that encompasses multiple sensory experiences, including taste and aroma. Taste is caused by non-volatile compounds (Khan et al., 2015), such as free amino acids, which are important taste substances and can produce flavors such as umami, sweetness, and bitterness (Meng et al., 2022). Aroma, on the other hand, is closely related to volatile compounds. In meat products, most of these are non-contributory or low-contributory aroma compounds, with only a small portion of volatile compounds affecting the overall aroma of the meat, known as key aroma compounds (Sohail et al., 2022). These flavor substances are produced through various chemical reactions, such as lipid oxidation, Strecker degradation, and the Maillard reaction, and include free amino acids, 5’-nucleotides, aldehydes, alcohols, and ketones (Wu et al., 2022). It has been reported that the free amino acids present in oysters directly influence taste; for example, Glu is crucial for umami, while Gly and Ala affect sweetness (Liu et al., 2021). 5’-nucleotides like AMP, GMP, and IMP are the most important components that contribute to umami (Liu et al., 2022). In terms of aroma, aldehydes, ketones, and alcohols are the most prominent volatile flavor compounds in oysters (Liu et al., 2023). Currently, the majority of flavor research focuses on how different strains, cultivation regions, and harvesting seasons affect the volatile profiles of oysters (Huang et al., 2019; Chen et al., 2024). Although there have been investigations into the flavor components of oysters with different ploidies, these studies have generally concentrated on the whole meat (Fu et al., 2023; Sun et al., 2023). However, the nutrient distribution in oysters varies not only by ploidy but also across different body parts (Li et al., 2022b), suggesting that volatile flavor compounds may also be distributed unevenly within the oyster’s tissues.

In recent years, with the continuous development of metabolomics, metabolomic tools have been widely used in the identification and analysis of key substances in food (Utpott et al., 2022). By comprehensively analyzing the metabolites in food, these tools can accurately identify and quantify important biomolecules, helping to reveal critical information about the nutritional value, flavor components, and safety of the food. Headspace Solid-Phase Microextraction combined with Gas Chromatography-Mass Spectrometry (HS-SPME-GC-MS) is a precise method for enriching and analyzing volatile or semi-volatile compounds in food (Jeleń et al., 2012). This technique not only allows for the identification, qualitative, and quantitative analysis of complex mixtures, but it also offers advantages such as speed and high accuracy. LC-MS technology is widely applied in food flavor analysis (Zhong et al., 2022). It can accurately separate and identify flavor compounds within complex matrices, particularly those that are non-volatile, highly polar, and thermally unstable. Both of these techniques are powerful means for exploring food flavors. For example, techniques such as HS-SPME-GC-MS and LC-MS have been used to characterize the structure, flavor, and texture of grass carp fed with broad beans (Fu et al., 2024). HS-SPME-GC-MS and metabolomics analysis methods have been employed to explore the flavor compounds related to odor deterioration in tilapia during refrigeration (Cheng et al., 2023). Therefore, metabolomic analysis are powerful tools for the comprehensive study of both non-volatile and volatile compounds in meat products. However, to our knowledge, few studies have used metabolomics to investigate the differences in flavor components between different ploidy levels of oysters and among their different tissues.

This study compares and evaluates the flavor profiles of different tissues in diploid and triploid oysters, based on metabolomics technology using LC-ESI-MS/MS and volatile analysis using HS-SPME-GC-MS. The findings are expected to provide fresh insights into the flavor characteristics of oysters based on ploidy and tissue type, which will be valuable for the future development and sustainability of oyster products.

Meat aroma is an important indicator of quality and influences consumer acceptance. Oysters can produce volatile compounds during the growth process that give them their own characteristic aroma. Therefore, different types of volatile compounds and their amounts result in food products carrying different aromas. In this study, the amount of volatile compounds in all four tissues of triploid oysters was higher than that of diploids. Aldehydes and alcohols are important volatile odors in volatile organic compounds, and the threshold of aldehydes is relatively low, which has a significant effect on the flavor of oysters (Zhang et al., 2009). Aldehydes are usually produced by oxidative degradation of polyunsaturated fatty acids. Short-chain aldehydes often have a “fresh, grass, green” smell, and as carbon atoms increase, they may give a strong “greasy and fatty” impression (Liu et al., 2023). The enaldehydes and dienaldehydes produced by the degradation of hydroperoxides of linoleate and linolenic acid esters usually have pleasant aromas, such as the creamy, cucumber and fatty aromas that give oyster characteristics (Aruna and Baskaran, 2010). The quantity and relative content of enal and dienal in the 4 tissues of triploid Portuguese oysters were more than those of diploid oysters. (E)-2-Decenal identified in the adductor muscle, hepatopancreas and gill of triploid oysters could produce grassy odor, while (E)-2-Nonenal unique in the gonads of triploid oysters could produce citrus and cucumber-like taste. In contrast, the threshold for alcohol compounds was relatively high, which did not significantly contribute to oyster flavor (Zhang et al., 2019). However, the threshold for unsaturated alcohols is relatively low, and these compounds contribute significantly to oyster flavor. Alcohols usually produce aromatic and vegetative aromas (Ma et al., 2021). Among them, 1-Octen-3-ol identified in both diploid and triploid oysters can produce a unique earthy and mushroom taste, while (E,Z)-3, 6-nonadien-1-ol identified separately in triploid oyster gills can produce a cucumber-like aroma.

Our study provides valuable insights into the distinct metabolic profiles of diploid and triploid oysters, focusing on lipids, nucleosides, amino acids, and other small molecules. One of the key findings was the significantly higher concentration of lipids and their derivatives in triploid oysters. We identified 281 lipids, including 126 glycerophospholipids, and observed that specific compounds such as N-Arachidonoyl-L-Alanine were notably upregulated in triploids, particularly in the gonadal gland, gill, and hepatopancreas. This compound, known for its potential anti-cancer properties, likely enhances both the nutritional value and flavor of triploid oysters. Phospholipids, in particular, are critical for flavor development during cooking (Sohail et al., 2022), and the elevated presence of oxidized lipids like (±) 5-HETE and Prostaglandin F2α in triploid oysters supports their role in generating volatile flavor compounds. These findings align with previous studies, which highlight the importance of lipid oxidation in seafood flavor formation, particularly through interactions with Maillard reaction products (Sohail et al., 2022), potentially explaining the richer taste of triploid oysters.

Regarding nucleosides, we identified 88 types, with significant increases in inosine, guanosine, and inosine diphosphate in triploid oysters. These nucleosides play key roles in nucleic acid synthesis, energy metabolism, and physiological regulation (Bucci, 2020). The elevated levels of inosine and its derivatives in triploids enhance umami taste and provide additional health benefits, such as improved liver function and immune system support (Koito et al., 2010). Our results are consistent with previous research demonstrating the importance of nucleosides in food for both flavor and nutritional enhancement (Kasumyan, 2016). In triploid oysters, the higher concentration of these compounds contributes to their superior flavor profile and their potential for greater health benefits compared to diploid oysters.

The amino acid profile also revealed significant differences between diploid and triploid oysters. We detected 244 amino acids and their derivatives, with particularly high levels of glutamate and aspartate, which are known for enhancing umami flavor, in triploid oysters. These amino acids are essential for the savory, rich taste associated with seafood, and their abundance in triploids supports the notion that these oysters offer a more complex and desirable flavor (Kasumyan, 2016). Additionally, the presence of free amino acids such as glycine, alanine, and proline, which are linked to sweet flavors, was significantly higher in triploid oysters. This is consistent with other studies that show these amino acids play a crucial role in flavor development during cooking or food processing (Zhang et al., 2023b). Moreover, the higher levels of taurine in triploid oysters, an amino acid known for its antioxidant properties and cardiovascular health benefits, further highlight the enhanced nutritional value of triploids (Koito et al., 2010).

Several small molecules, including vitamins and coenzymes, were more abundant in triploid oysters. Notably, Nicotinamide (vitamin B3) was significantly higher in triploids, suggesting enhanced metabolic benefits (Mehmel et al., 2020). Nicotinamide is essential for energy metabolism and redox reactions, and its presence highlights the potential health advantages of consuming triploid oysters. In contrast, diploid oysters showed higher levels of 25-Hydroxycholesterol, a compound involved in bile acid biosynthesis, which indicates distinct metabolic pathways between diploid and triploid oysters (Zhang et al., 2023a). These differences open avenues for further research, particularly regarding how these metabolites influence flavor and health outcomes in human diets.

Our research demonstrates that triploid oysters have a more complex and beneficial metabolic profile than diploid oysters, with significant enhancements in lipids, nucleosides, amino acids, and small molecules that contribute to both superior flavor and nutritional value. These results advance our understanding of oyster metabolomics and provide a foundation for future research aimed at optimizing the cultivation of triploid oysters to improve both taste and health benefits. Further studies could explore the environmental and genetic factors influencing these metabolic differences, as well as the bioavailability and long-term health impacts of these enriched metabolites in human diets.

This study used a metabolomics approach to distinguish the flavor profiles of diploid and triploid oysters, revealing significant biochemical differences. Our findings demonstrate that triploid oysters exhibit a more complex array of metabolites and higher concentrations of compounds that enhance both flavor and nutritional value. Notably, triploid oysters contain elevated levels of essential amino acids, nucleotides, and taurine, contributing to their richer taste and potential health benefits. The adductor muscle, gills, and gonads of triploid Portuguese oysters showed more pronounced pleasant aromas compared to diploids, characterized by green, fruit, and cucumber-like fragrances, giving triploids a stronger aroma, while the ketones in the diploid oyster hepatopancreas had a stronger floral and fruity taste than in triploids. The differential metabolic profiles, including higher levels of umami-enhancing nucleotides and sweet-tasting amino acids in triploids, suggest these oysters may offer a superior culinary experience along with enhanced nutritional benefits. The presence of bioactive peptides with potential health-promoting properties further highlights the value of triploid oysters in a balanced diet. Additionally, this research provides key insights into the metabolic pathways influenced by oyster ploidy, with important implications for aquaculture and food science. Understanding these pathways will help optimize breeding programs to enhance flavor and health qualities, contributing to the sustainable development of the oyster aquaculture industry. This study lays a foundational framework for selecting flavor phenotypes in triploid oysters, aiming to enhance consumer satisfaction and health outcomes through targeted breeding and cultivation practices, with future research needed to explore the long-term health impacts of consuming triploid oysters and further investigate the metabolic mechanisms behind the observed differences in taste and nutritional content.