{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,30]],"date-time":"2026-06-30T10:46:54Z","timestamp":1782816414145,"version":"3.54.5"},"reference-count":39,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2025,12,18]],"date-time":"2025-12-18T00:00:00Z","timestamp":1766016000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Foreign Cooperation Project of Fujian Academy of Agricultural Sciences","award":["DWHZ-2024-2"],"award-info":[{"award-number":["DWHZ-2024-2"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Marine Drugs"],"abstract":"<jats:p>Oyster peptides (OPs) have gained increasing attention for their excellent biological activities, especially immunomodulatory effects. In this study, oyster proteins were fermented using Lactobacillus casei to prepare bioactive peptides, and the effects of fermentation parameters (time, temperature, and inoculum amount) on the degree of hydrolysis (DH) were optimized. The optimal fermentation conditions were determined as 30 h, 35 \u00b0C, and 5% inoculum amount, resulting in a DH of 28.24%. Structural characterization showed that OPs were mainly composed of low-molecular-weight peptides (&lt;1000 Da) with high hydrophobic amino acid content, and they exhibited good stability during in vitro gastrointestinal digestion. In vitro immunological evaluation using RAW264.7 macrophages demonstrated that OPs significantly enhanced phagocytic activity and nitric oxide (NO) production, and upregulated the mRNA expression levels of pro-inflammatory cytokines including interleukin (IL)-6, IL-1\u03b2, and tumor necrosis factor (TNF)-\u03b1. Mechanistically, OPs exerted immunostimulatory effects by specifically activating the extracellular signal-regulated kinase (ERK) pathway within the mitogen-activated protein kinase (MAPK) signaling cascade, without significant alterations in the phosphorylation levels of p38 and c-Jun N-terminal kinase (JNK). These findings highlight the potential of Lactobacillus casei-fermented oyster peptides as natural immunomodulatory ingredients for functional food development.<\/jats:p>","DOI":"10.3390\/md23120484","type":"journal-article","created":{"date-parts":[[2025,12,18]],"date-time":"2025-12-18T11:08:28Z","timestamp":1766056108000},"page":"484","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Oyster Peptides Prepared by Lactobacillus casei Fermentation Enhance Immune Activity in RAW264.7 Cells via Activation of the MAPK Pathway"],"prefix":"10.3390","volume":"23","author":[{"ORCID":"https:\/\/orcid.org\/0009-0002-8941-4711","authenticated-orcid":false,"given":"Lingyue","family":"Zhong","sequence":"first","affiliation":[{"name":"Institute of Food Science and Technology, Fujian Academy of Agricultural Sciences, Fuzhou 350003, China"},{"name":"Yuanzhidao-FAAS Joint Innovation Center for Functional Probiotics & Medicinal-Edible Resources, Xiamen 361199, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yirui","family":"Wu","sequence":"additional","affiliation":[{"name":"College of Food Science, Fujian Agriculture and Forestry University, Fuzhou 350002, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xuefang","family":"Guan","sequence":"additional","affiliation":[{"name":"Institute of Food Science and Technology, Fujian Academy of Agricultural Sciences, Fuzhou 350003, China"},{"name":"Yuanzhidao-FAAS Joint Innovation Center for Functional Probiotics & Medicinal-Edible Resources, Xiamen 361199, China"},{"name":"Fujian Key Laboratory of Agricultural Product (Food) Processing, Fuzhou 350003, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mei","family":"Xu","sequence":"additional","affiliation":[{"name":"Yuanzhidao-FAAS Joint Innovation Center for Functional Probiotics & Medicinal-Edible Resources, Xiamen 361199, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2127-840X","authenticated-orcid":false,"given":"Juqing","family":"Huang","sequence":"additional","affiliation":[{"name":"Institute of Food Science and Technology, Fujian Academy of Agricultural Sciences, Fuzhou 350003, China"},{"name":"Yuanzhidao-FAAS Joint Innovation Center for Functional Probiotics & Medicinal-Edible Resources, Xiamen 361199, China"},{"name":"Fujian Key Laboratory of Agricultural Product (Food) Processing, Fuzhou 350003, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5378-9058","authenticated-orcid":false,"given":"Yafeng","family":"Zheng","sequence":"additional","affiliation":[{"name":"College of Food Science, Fujian Agriculture and Forestry University, Fuzhou 350002, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5324-8988","authenticated-orcid":false,"given":"Qi","family":"Wang","sequence":"additional","affiliation":[{"name":"Institute of Food Science and Technology, Fujian Academy of Agricultural Sciences, Fuzhou 350003, China"},{"name":"Yuanzhidao-FAAS Joint Innovation Center for Functional Probiotics & Medicinal-Edible Resources, Xiamen 361199, China"},{"name":"Fujian Key Laboratory of Agricultural Product (Food) Processing, Fuzhou 350003, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,12,18]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"145549","DOI":"10.1016\/j.foodchem.2025.145549","article-title":"Oyster (Crassostrea hongkongensis) protein isolates: Influence of extraction pH on physicochemical, conformational and functional properties","volume":"492","author":"Liu","year":"2025","journal-title":"Food Chem."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"101","DOI":"10.12717\/DR.2023.27.3.101","article-title":"The Annual Reproductive Cycle, Proximate Composition, Fatty Acid and Amino Acid Content of Pacific Oyster, Crassostrea gigas (Magallana gigas), in Gadeok-do, Korea","volume":"27","author":"Cho","year":"2023","journal-title":"Dev. 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