Undaria pinnatifida sporophyll (U. pinnatifida) is a major byproduct of U. pinnatifida (a brown algae) processing. Its phenolic constituents, phlorotannins, are of special interest due to their intrinsic ability to precipitate proteins. Herein, a high-temperature extraction procedure was used to isolate these biologically active compounds. The heating temperature, heating time, and extraction solvent (ethanol) concentration were examined with response surface analysis to determine the optimal conditions to achieve the maximum extraction rate. The analysis revealed the optimal conditions to be: 170 °C of heating temperature, 5.2 h of heating time, and 52% ethanol concentration for a yield of 10.7 ± 0.2 mg gallic acid equivalent/g dry weight (GAE/g DW) of sample. Compared to epigallocatechin gallate (EGCG), the extracted phlorotannins displayed higher antioxidant activity on H₂O₂-induced RAW 264.7 cells with improved efficiency. Furthermore, the compounds exhibited strong anti-inflammatory activity. These findings potentially can be utilized to guide development of novel functional foods and food supplements from sea-originated resources such as brown algae.

Saccharina japonica belongs to brown macro-alga with various potential health benefits; its antioxidant and anti-inflammatory activities indicate the potential to improve inflammatory bowel diseases. Here, the potential anti-colitis effect of Saccharina japonica extract (SJE) was evaluated on dextran sulfate sodium (DSS)-induced ulcerative colitis (UC) in C57B/L6 mice. The mice were treated with mesalazine (MES) and various doses of SJE by gavage for 14 days. Results showed that both MES and SJE treatment decreased the disease activity index scores, relieving the short colon. SJE increased the occludin and zonula occludens-1 levels, and the beneficial effects were better than MES. MES and SJE exerted similar effects in decreasing inflammatory cytokines and oxidative stress. Moreover, SJE reshaped the intestinal microbiota by increasing α-diversity and reducing plenty of harmful bacteria. Dietary SJE was significant to relieving the reduction in short-chain fatty acids. The results revealed the protective effect of SJE on colitis and potential mechanisms, which is important for the rational use of SJE in UC prevention.

Sea cucumber (Apostichopus japonicus) is an economically significant species in China having great commercial value. It is challenging to maintain the textural properties during thermal processing due to the distinctive physiochemical structure of the A. japonicus body wall (AJBW). In this study, the gene expression profiles associated with tenderization in AJBW were determined at 0 h (CON), 1 h (T_1h), and 3 h (T_3h) after treatment at 37 °C using Illumina HiSeq™ 4000 platform. Seven-hundred-and-twenty-one and 806 differentially expressed genes (DEGs) were identified in comparisons of T_1h vs. CON and T_3h vs. CON, respectively. Among these DEGs, we found that two endogenous proteases—72 kDa type IV collagenase and matrix metalloproteinase 16 precursor—were significantly upregulated that could directly affect the tenderness of AJBW. In addition, 92 genes controlled four types of physiological and biochemical processes such as oxidative stress response (3), immune system process (55), apoptosis (4), and reorganization of the cytoskeleton and extracellular matrix (30). Further, the RT-qPCR results confirmed the accuracy of RNA-sequencing analysis. Our results showed the dynamic changes in global gene expression during tenderization and provided a series of candidate genes that contributed to tenderization in AJBW. This can help further studies on the genetics/molecular mechanisms associated with tenderization.

α-amylase can effectively inhibit the activity of digestive enzymes and alter nutrient absorption. The impact of ovum hydrolysates of sea cucumbers on α-amylase activity was investigated in this study. The protein hydrolysates generated using different proteases (pepsin, trypsin, and neutral protease) and molecular weights (less than 3000 and more than 3000) were investigated. The results showed that all three different hydrolysates demonstrated calcium-chelating activity and induced a fluorescence-quenching effect on α-amylase. The sea cucumber ovum hydrolysate with a molecular weight of less than 3000 Da, isolated using trypsin, showed the most effective inhibitory effect on α-amylase, with an inhibition rate of 53.9%, and the inhibition type was identified as mixed forms of inhibition. In conclusion, the generation and utilization of protein hydrolysates from sea cucumber ovum as a functional food ingredient could be a potential approach to add value to low-cost seafood by-products.

Collagen fibers (CFs) are essential in maintaining the structural integrity of sea cucumber body wall tissues. Addition of Ca²⁺ to meat products improves tenderness and modulates the levels of chemical interactions in CFs. In this study, we investigated the effects of Ca²⁺ (ranging from 0 to 40 mM) on the structural organization and thermal stability of CFs. The dissolution of protein and polysaccharide of sea cucumber collagen fiber was less under low concentration of Ca²⁺ (2.5 mM–10 mM), and the dissolution amount corresponding to high concentration of Ca²⁺ (20 mM, 40 mM) increased. FTIR, XRD, DSC, TGA and SEM analyses revealed that low concentrations of Ca²⁺ (2.5 and 5 mM) increased the intermolecular binding of CFs, enhanced stability of triple helix structure, maintained the structural integrity of CFs, and inhibited the degradation of CFs. This study provides insights into enhancing the quality of sea cucumber through low-temperature tenderization.