Biological Function Evaluation And Selenium Enrichment Technology Of Lactic Acid Bacteria Selenium

Selenium is an essential trace element for maintaining human life activities and participates in multiple important physiological functions of the body.Se deficiency can lead to many adverse symptoms such as immune system disorders,increased risk of cardiovascular diseases,and Kashin-Beck disease.More than 70%of the regions in China are deficient in Se or belong to Se-poor areas.Therefore,Se supplements have appeared in the market,but they are mainly based on Se-enriched yeast and Na₂Se O₃.Researchers are committed to developing new Se supplements.LAB-Se belongs to a new organic Se form.The dual advantages of LAB activity and organic Se indicate that LAB-Se has huge potential as a new type of Se supplement.However,current research focuses on the Se enrichment ability of LAB,and the forms and functional advantages of LAB-Se are not yet clear.In the early stage of this study,the research group screened a LAB strain,Lactobacillus paracasei（CCFM1089）,which can enrich selenocysteine（Se Cys）and has up to 89%Se Cys in organic Se after Se-enrichment culture.This project evaluated the biological functions of Se-CCFM1089 through animal experiments and compared them with two mature Se supplements.Then,based on the advantages of the form and function of LAB-Se,more LAB with high enrichment of Se Cys were screened out.Finally,the best strain for Se supplementation in the body was optimized for Se enrichment to improve its ability.The main research contents are as follows:（1）DSS-induced colitis was used as a model to evaluate the biological functions of LAB-Se and study the effect of Se on mice immune-inflammatory responses.Mice were fed with Se-deficient diet to avoid the influence of Se contained in mice themselves.The experimental groups were orally administered with active Se-CCFM1089 and inactivated Se-CCFM1089,with CCFM1089,Se-enriched yeast（rich in Se Met）,and Na₂Se O₃ as control groups.The results showed that Se-CCFM1089,Se-enriched yeast and Na₂Se O₃were able to alleviate the inflammatory symptoms of mice,showing an increase in colon length and a decrease in pro-inflammatory cytokines（IL-6,TNF-αand IL-1β）levels.Compared with the control groups,the colon mucosa of mice in the LAB-Se group was intact,with a high secretion of goblet cells and only a few inflammatory cells infiltrating.Additionally,LAB-Se could significantly increase the activity of selenoenzyme（GSH-Px）,and active LAB-Se had a better alleviating effect on DSS-induced colitis than inactivated LAB-Se.（2）The efficacy of LAB-Se in treating liver-related diseases was studied using an acoholic liver disease（ALD）mice model.To further investigate the advantages of LAB-Se,two doses of low and medium were evaluated for their alleviating effect on ALD and compared with Se-enriched yeast and Na₂Se O₃.The results showed that LAB-Se could effectively alleviate ALD in mice.Even low-dose LAB-Se could significantly alleviate ALD.Specifically,LAB-Se intervention resulted in weight gain recovery,reduced liver tissue swelling,reduced pathological damage and inflammation degree of liver tissue,decreased activity of AST and ALT in serum,restored ileal barrier function,and increased antioxidant capacity of the body.The ability of LAB-Se to increase selenoenzyme activity is still found to be superior to other Se supplements,and the ability of active LAB-Se to increase selenoenzyme activity is stronger than that of inactivated LAB-Se.According to the experimental results,the mechanism of LAB-Se in alleviating ALD may be to inhibit the expression of keap-1,up-regulate the expression of Nrf2 signal and its downstream targets,thereby improving the antioxidant capacity of the body.LAB-Se can also inhibit the up-regulation of TLR4-mediated NF-κB,reduce the level of pro-inflammatory cytokines in the body,and achieve the effect of alleviating liver damage.（3）Two sets of experimental results showed that Se-enriched CCFM1089 has good Se supplementation effects,can significantly improve selenoenzyme activity in the body,alleviate symptoms of related diseases,and indirectly indicate that Se Cys has better probiotic effects.Moreover,the activity of LAB also promotes Se Cys to exert better efficacy in the body.Therefore,three strains of LAB have been newly screened that can enrich Se Cys effectively.They are Limosilactobacillus reuteri CCFM1303（total Se content of 530.7 mg/kg,Se Cys accounts for 98.4%of the organic Se）,Lactobacillus acidophilus CCFM1304（total Se content of 453.1 mg/kg,Se Cys accounts for 95.3%of the organic Se）,and Lactobacillus gasseri CCFM1305（total Se content of 557.9 mg/kg,Se Cys accounts for 93.5%of the organic Se）.（4）Through Se-deficient mice experiments to compare the Se supplementation effects of Se-CCFM1089 and the newly three screened LAB-Se,and Se-CCFM1303 with the best effect was selected.A Se-enrichment process was optimized for CCFM1303 through amino acids,nitrogen sources,salt stress,p H,and Se addition time to increase its biomass and Se-enrichment ability.The results showed that when the medium components were anhydrous glucose 20 g/L,yeast extract FM803 20 g/L,anhydrous sodium acetate 2 g/L,diammonium hydrogen citrate 2g/L,K₂HPO₄ 2 g/L,Mg SO₄·7H₂O 0.1 g/L,Mn SO₄·H₂O 0.05 g/L,Na₂Se O₃ 6.57 mg/L,Tween80 1 m L/L,serine 0.35 g/L,Na Cl 30 g/L,and the p H was 5.5 under optimized culture conditions,the Se content of CCFM1303 was up to 849.6 mg/kg,and the OD₆₀₀ was 2.1 when Se was added to the medium after the seed liquid was inoculated and grown for 6 hours.