Research Progress of Selenium-Enriched Foods

**Background:** Selenium is an essential micronutrient that is metabolized into 25 selenoproteins with antioxidant, anticancer, and fertility-improving functions. Selenium deficiency affects approximately one billion people and is linked to diseases such as Keshan disease, Kashin-Beck disease, myocardial infarction, Alzheimer's disease, and chronic pancreatitis. Conversely, excessive selenium intake can cause toxicity, including hair loss, skin lesions, type 2 diabetes, and intestinal diseases. The bioactivity and bioavailability of selenium depend on its chemical species, with organic selenium (e.g., selenomethionine, selenocysteine) being less toxic and more bioavailable than inorganic forms (e.g., selenate, selenite). To address deficiency, selenium-enriched foods have been developed through plant, animal, and microbial transformations. This review focuses on the metabolism of selenium, the physiological functions of selenium-enriched foods, and analytical methods for total selenium and its species.

**Methods:** This is a narrative review that synthesizes findings from multiple studies on selenium-enriched foods. The authors describe the metabolism of different selenium species (Se(IV), Se(VI), SeCys, MeSeCys, SeMet, SeCys2) in organisms, noting that all are eventually converted to hydrogen selenide (H2Se) for selenoprotein synthesis. The review categorizes selenium-enriched foods into natural (from high-selenium soil) and artificial (via plant, animal, or microbial transformation). Plant transformation methods include soil fertilization, foliar fertilization, and hydroponic fertilization. Animal transformation involves feeding selenium supplements to livestock to produce selenium-enriched meat, dairy, and eggs. Microbial transformation uses inorganic selenium in culture media to produce selenium-enriched yeast and fungi. The physiological functions of these foods are discussed based on in vitro and in vivo studies, including antioxidant, anti-inflammatory, anticancer, detoxification, and male fertility improvement effects. Analytical methods for total selenium (e.g., HG-AFS, ICP-OES, ICP-MS) and selenium species (e.g., HPLC-ICP-MS, CE-ICP-MS, GC-ICP-MS) are reviewed, with emphasis on sample pretreatment (water, acid, enzymatic extraction) and separation/detection techniques.

**Key Results:** The review reports that selenium-enriched foods exhibit diverse physiological functions. For example, selenium-enriched polysaccharides from Pleurotus ostreatus reduced hydrogen peroxide-induced oxidative stress in murine skeletal muscle cells. Selenium-enriched yeast protein hydrolysate increased glutathione peroxidase and catalase activities in vivo. Selenium-enriched ricegrass juice extracts reduced nitric oxide levels in LPS-induced RAW264.7 cells. Selenium-enriched Cordyceps militaris inhibited the viability of NCI-H292 and A549 cancer cells and induced apoptosis. Selenium-enriched rice alleviated cadmium poisoning in mice by overexpressing antioxidant genes (Nrf-2, GPX1, TrxR2, TNF-2). Selenium-enriched probiotics protected carp from mercury-induced inflammation. Selenium-enriched green tea inhibited chromosomal aberrations in mouse testicular cells. Selenium-enriched yeast improved male fertility in roosters. Analytical methods showed that total selenium content in various foods ranged from 0.01 mg/kg (vegetables) to 2145 mg/kg (yeast). HPLC-ICP-MS achieved detection limits of 0.44–2.35 μg/L for selenium species. In selenium-enriched yeast, SeMet accounted for 67% of total selenium (3434 ± 19 μg/g).

**Clinical Implications:** Selenium-enriched foods offer a safe and effective strategy for selenium supplementation, particularly in populations with deficiency. The review emphasizes that organic selenium species are more bioavailable and less toxic than inorganic forms. The demonstrated antioxidant, anti-inflammatory, and anticancer activities suggest potential therapeutic roles in chronic disease prevention. The detoxification effects against heavy metals (cadmium, mercury, lead) indicate possible applications in environmental toxicology. The improvement of male fertility highlights reproductive health benefits. However, the authors note that most studies are preclinical, and further clinical trials are needed to confirm efficacy and safety in humans. Accurate analytical methods, especially ICP-MS-based techniques, are crucial for quality control and to ensure that selenium-enriched foods meet nutritional standards without exceeding toxic thresholds. The review calls for more research on the mechanisms of action and long-term effects of selenium-enriched foods.