Optimization Of Fermentation Conditions Of Rufibacter Hautae NBS58-1 Exopolysaccharide And Its Structure And Function

Microbial exopolysaccharides（EPS）are biological polymers that have a protective effect on themselves produced by microorganisms in the process of growth and metabolism,which have low acquisition costs and simple preparation methods,and also as natural,non-toxic and biodegradable resources.Microbial EPS has a variety of biological activities,such as antioxidant,emulsification,antibacterial and immunomodulation,etc.,and has high economic value and broad application prospects in medicine,food,chemical industry and other fields.EPS from different microorganisms have different physicochemical properties and antioxidant activities.In this paper,the fermentation conditions,structure and activity of EPS from Rufibacter hautae NBS58-1 were studied,which provides theoretical and technical reference for its application in food,medicine and other industries.The main research contents and results of this paper are as follows:1.The strain NBS58-1 was cultured in R2A liquid medium,and crude exopolysaccharides were extracted from the fermentation broth by ethanol precipitation method,and further separated and purified by gel column chromatography to obtain the strain NBS58-1exopolysaccharide RH-EPS.The physicochemical characteristics,emulsification and antioxidant activities were characterized through SEM,AFM,HPLC,GPC,FTIR,NMR,TG-DSC and Congo red analyses.Results showed that RH-EPS is a heteropolysaccharide（2141 Da）with a rough,dense and porous sheet structure on the surface,composed of mannose,glucose,ribose,fucose,glucuronic acid,arabinose,galactose,xylose,rhamnose and galacturonic acid with a molar ratio of 34.40:26.35:12.24:8.19:5.57:5.13:3.35:1.45:0.63:0.09,in which there wereα-andβ-configuration of pyranose units.Its degradation temperature was 277.99°C.2.Compared to Tween 80,RH-EPS was an efficient emulsifier for olive oil,diesel,gasoline and xylene.The results of antioxidant experiments showed that RH-EPS exhibited good scavenging ability and reducing activity for hydroxyl,DPPH,ABTS radicals and iron ions.RH-EPS could protect porcine intestinal epithelial cells（IPEC-1）by reducing H₂O₂-induced oxidative damage,and with the increase of RH-EPS concentration,the activities of antioxidant enzymes CAT,GSH-PX,SOD and the content of lipid peroxide MDA in the IPEC-1 cells can return to the normal level.This suggested that RH-EPS was expected to be developed as an antioxidant,emulsifier,etc.for applications in the food,pharmaceutical and other industries.3.Aimed to increase the production of EPS from Rufibacter hautae NBS58-1 by liquid-state fermentation,the conditions of EPS produced by fermentation of strain NBS58-1were optimized by single factor and response surface test.The results showed that the optimal production conditions of EPS from strain NBS58-1 were initial p H 7.5,temperature23℃,sucrose 14.13 g/L,yeast extract 1 g/L,soluble starch 0.5 g/L,K₂HPO₄·3H₂O 0.3 g/L,Mg SO₄·7H₂O 0.05 g/L and sodium pyruvate 0.3 g/L.Under these conditions,the EPS yield was 138.85 mg/L,which was 3.08 times that of before optimization.