Study On Metabolic Analysis Of Saccharomyces Boulardii Incubated With Chinese Yam And Radioprotection Effect Of Ethanol Extract From Yeast-fermented Chinese Yam

Ionizing radiation（IR）has been widely used in the medical and food industries.However,certain damage to the body will be caused by long-term exposure to IR,which even induces cancer in severe cases.One of the new approaches to radiation protection is radioprotective functional foods from natural compounds or microbial metabolites,which could reduce the oxidative damage caused by radiation and improve the physical health.As one of the homologous plants of medicine and food,Chinese yam（Dioscorea opposita Thunb.）is rich in nutrients and functional active factors.However,its comprehensive utilization and related fermented deep-processed products are still limited.As a probiotic yeast,Saccharomyces boulardii possesses favorable bioactivities such as antioxidant,immunomodulation and so on.Recently,its potential application has been gradually explored in the field of food fermentation.In this study,we used S.boulardii to ferment Chinese yam for deep processing,the fermented Chinese yam ethanol extract（FCYE）was preliminarily prepared and its main components were identified based on fermentation metabolites analysis,and its further radioprotection was also investigated in vitro and in vivo.The main research contents were as follows:（1）The determination of main components and metabolites analysis of fermented Chinese yamIn this study,the fermentation metabolites were studied as the research object,and the differential analysis of the main components between unfermented and fermented Chinese yam was performed and the metabolic pathways relative to synthesis of some main differential metabolites were investigated.The results showed that the content of total sugar reduced significantly and the contents of protein and total flavonoids both increased.Further analysis based on metabolomics found that the significantly up-regulated metabolites in fermented Chinese yam were mainly bioactive components such as organic acids,flavonoids and nucleotide derivatives,which initially revealed the distribution of bioactive substances was concentrated on alcohol-soluble small molecular substances in fermented Chinese yam.（2）Components identification and in vitro radioprotection study of FCYEBased on the metabolites analysis of fermented Chinese yam,FCYE was obtained along with the identification of main functional components and the in vitro bioactivity.Through UPLC-MS/MS,it was found that organic acids（such as 2-Hydroxyisocaproic acid,DL-3-Phenyllactic acid,etc.）were the most abundant component in FCYE,followed by flavonoids and phenolic acids（such as Naringenin,2-Hydroxy-3-phenylpropanoic acid,etc.）.The in vitro bioactivity assay showed that FCYE possessed excellent total reducing power,DPPH free radical scavenging activity and ABTS free radical scavenging activity in the concentration range of 1.0-5.0 mg/m L.Besides,when the concentration was 1-50μg/m L,FCYE obviously increased the proliferation activity of RAW264.7 cells,correspondingly signally enhancing the cell phagocytosis function and NO production ability.Finally,the in vitro radioprotection potential of FCYE was preliminarily explored based on the establishment of ⁶⁰Co-γradiation oxidation injury model on normal cells.It was indicated that FCYE exhibited a significant radioprotective effect both on AML-12 cells and HCo Epi C cells.Comprehensive analysis presented that excellent antioxidant activity,immunomodulatory function and in vitro radioprotective effect existed in FCYE,which could be a potential candidate for natural radioprotectors.（3）The radioprotection study of FCYE on IR-induced injury in miceThrough the establishment of ⁶⁰Co-γradiation oxidation injury mice model,we investigated the in vivo radioprotective effect of FCYE.Results showed that the oxidative damages of various organs and tissues（including spleen,liver and small intestine）in IR-induced injured mice could be significantly alleviated by FCYE.The antioxidant defense function of mice was able to be distinctly improved by strengthening SOD activity,increasing GSH content and reducing MDA level;and meanwhile the overall immune function of mice could be boosted by enhancing the number of lymphocytes,improving immune organ index and regulating inflammatory factors levels（IL-2 and TNF-α）,which finally helped FCYE exert an excellent in vivo radioprotective effect.In conclusion,FCYE presented good antioxidant activity,immunomodulatory function and radioprotective effect.Its mechanism was speculated to be closely related to the improvement of antioxidant defense system and the enhancement of immune function in the body.Our research could lay a theoretical foundation for the development and application of natural radioprotectors and radiation protection functional food,which also provided a new reference for comprehensive utilization of Chinese yam.