Yujun Liu

Sea cucumber Apostichopus japonicus is one of the few animals capable of synthesizing saponins, which are critical components of its nutritional quality and health-beneficial properties. However, the specific mechanism underlying saponin biosynthesis in sea cucumbers remains unclear despite previous investigations. This study aimed to characterize the molecular pathway and regulatory mechanism of saponin biosynthesis in A. japonicus. Thirteen candidate genes involved in de novo saponin skeleton synthesis were identified from the A. japonicus genome, and their full-length cDNAs were obtained via PCR-RACE. Sequence analysis predicted the intracellular localization of these genes. Combined in situ hybridization and quantitative real-time PCR analyses revealed their high expression in coelomocytes, indicating coelomocytes as the primary saponin synthesis sites. Knockdown of mevalonate kinase (AjMVK) and two oxidosqualene cyclases (AjPS and AjLS) caused a more obvious decrease in saponin levels, identifying them as key biosynthetic enzymes. Yeast two-hybrid assays revealed that AjPS and AjLS interact with ficolins, complement component 3-2, O-linked β-N-acetylglucosamine transferase, and α-L-fucosidase, whose regulatory effects were further validated by RNA interference and saponin content measurements. These results suggest that saponin biosynthesis in A. japonicus is regulated by the complement lectin pathway and modulated by glycosylation enzymes, providing a molecular foundation for enhancing bioactive saponin production for pharmaceutical and nutraceutical applications.

A non-targeted metabolomics technique was employed to investigate the dynamic metabolite changes of scallop (Patinopecten yessoensis) adductor muscle (SAM) and scallop mantle (SM) during the early (E), middle (M), and late (L) harvest period from June to July. Many more metabolites were identified from SM (831) than from SAM (231), and 24 and 12 significantly differential metabolites were screened, respectively. Organic acids and derivatives, lipids and lipid-like molecules, and organoheterocyclic compounds were the primary metabolite classes in both SAM and SM. In SAM, the levels of most altered metabolites, such as butyryl carnitine, (±)8-HEPE, 14(S)-HDHA, l-Kynurenine, and l-(−)-Methionine), decreased with the extended harvest time, whereas pipecolic acid and oleamide increased. Conversely, in SM, linoleamide, oleamide, dimethyl citrate, kynurenine, and pipecolic acid declined, while 5,6-Dihydrothymidine, dimethylsulfoniopropionate, and 13(S)-HOTrE increased with a longer harvest time. Pipecolic acid, exhibiting an obvious up-regulated response during the whole harvest period, was found to be the sole differential metabolite shared by SAM and SM. Annotation analysis showed that five metabolites were respectively identified in SAM and SM, and these metabolites were separately related to five metabolic pathways with slight differences among the two tissues. Amino acid metabolism/degradation and fatty acid metabolism were the primary pathways. These findings could provide new insights into the dynamic quality changes of scallops during the harvest period and may play a potential guiding role in the aquaculture and harvest of scallops.

This study aimed to systematically investigate and compare the biochemical composition of 13 locally abundant shellfish species (Dalian, China) and the taste characteristics of these shellfish and their boiling liquids. The results showed that Chlamys farreri exhibited the highest level of protein (64.58%) and polyunsaturated fatty acids (53.84% of total fatty acids), whereas Scapharca subcrenata showed a better composition and proportion of essential amino acids (EAA/TAA = 39.02%, EAA/NEAA = 63.98%) compared to other species. Glu, Gly, Ala, Arg, 5′-monophosphate (GMP), lactic acid, succinic acid, and malic acid were quantitatively determined as the main taste compounds in shellfish and their boiling liquids. The equivalent umami concentration (EUC) values, reflecting the synergistic effect of umami compounds, showed distinct characteristics, and the maximum umami intensities were found in Meretrix meretrix (586.8 g monosodium glutamate (MSG)/100 g) and the boiling liquid of Clinocardium californiense (358.3 g MSG/100 g), respectively. Based on these experimental results, C. californiense was found to have the highest prehensive quality score as revealed by principal component analysis (PCA). These results are important for promoting studies aimed at nutritional value development and taste compounds improvement of these shellfish species, especially for flavor enhancer development. Meanwhile, different shellfish species can be comprehensively developed and utilized based on their distinct nutritional properties, and this would translate into greater profitability for producers.

Hot-air drying is a key step for Antarctic krill (Euphausia superba) onboard processing; however, few studies have explored the effects of different drying temperatures on the quality and flavor alternations of Antarctic krill. In this study, we investigated the effects of hot-air drying temperatures on the physicochemical properties and flavor of Antarctic krill. Sensory evaluation, as well as physical and chemical property tests, revealed that Antarctic krill treated with hot-air drying exhibited substantial changes in moisture status, lipid oxidation indices, and b* value. The sensory evaluation of Antarctic krill under high temperatures (120 °C and 150 °C) showed higher scores (8.45 ± 0.05 and 8.58 ± 0.22, respectively) on smells, whereas the color changes caused by high temperatures also resulted in lower overall sensory evaluation scores. The POV and TBARS values reached the highest at 26.63 ± 0.28 mg/g and 1.45 ± 0.19 mg/100 g, respectively. The b* value decreased significantly to 22.32 ± 4.56 following 150 °C treatment. Furthermore, a total of 53 volatile compounds were identified by GC-IMS, and the results showed that aldehydes, alcohols, alkanes, ketones, pyrazines, and furans were the main flavor sources of Antarctic krill. At the same time, the GC-MS results showed that the thermal process had no significant effect on the nutrient content of Antarctic krill. The findings obtained in this study provide foundational information for future research on ship-borne processing and high-value utilization of Antarctic krill.

To investigate the regulatory effect of a bacteriocin-producing strain of Enterococcus faecalis DH9003 on the gut microbiota of mice, 15 healthy C57 male mice were randomly administered an equal volume of sterile normal saline (HD, control group, n = 7) and E. faecalis DH9003 (YD, treatment group, n = 8) via gavage. Metagenomic and metabolomic analyses were performed to determine the composition and metabolic function of the intestinal microbiota in mice. The results showed that the relative abundance of Firmicutes continuously increased over time in YD compared to HD. The number of E. faecalis DH9003 increased slowly and remained steady from days 7 to 28, indicating that E. faecalis DH9003 could colonize a considerable number of mouse guts via intragastric administration. Supplementation with E. faecalis DH9003 demonstrated a regulatory effect on the intestinal microbiota composition of mice, causing a shift in the relative abundance of Bacteroidetes and Firmicutes at the phylum level. In addition, a total of 2426 different metabolites were found in mouse feces, including 1286 and 1140 metabolites in positive and negative modes, respectively. Vitamin B6 and succinate were the most regulated and downregulated metabolites in negative ion mode, and the most upregulated and downregulated metabolites in positive ion mode were N-methyl-glutamic acid and N-octanoyl sphingosine. In conclusion, E. faecalis DH9003 can colonize mice gut, affecting the gut microbiota and metabolic competence. This strain therefore offers considerable potential for application as a probiotic.

Using Antarctic krill (Euphausia superba) as the research object, we optimized the process conditions for Antarctic krill sauce (AkS) by including three factors (salt addition, rock sugar addition, and the oil-to-material ratio) and sensory evaluation as response values. The data from the response surface were fed into the back propagation (BP) neural network training, generating a model mapping the process conditions and sensory scores, which were subsequently combined with the genetic algorithm (GA) for global optimization to determine the optimal process for AkS preparation. The results revealed that the response surface model was well suited to the BP neural network training and prediction sets, with correlation values of 0.98 and 0.95, respectively. The fitting prediction effect was obvious for the sensory scoring results of the product. The parameters obtained from the GA’s global optimization search accord with the analytical results of the response surface. The findings demonstrated that combining a BP neural network with a GA can enhance the AkS preparation technique. Under optimal processing conditions, AkS has a high sensory score and protein and carbohydrate contents, moderate fat content, minimal fat oxidation, and non-detectable pathogens, indicating that the AkS in this study was nutritious and safe to consume.