| Yeast is surrounded by a tough, rigid cell wall that represents 20-25% of the dry weight of the cell. Mannan is one of the major components (together with glucan, chitin and protein) of the yeast cell wall, occupying about 35-45% of it deposited in the outside of the cell wall. The present of mannan not only provide the cells with rigidity that protects them from osmotic pressure but also helps to maintain their shapes during the cell cycle stage. It has been reported that most of the immunological effects observed within the intact yeast cells are reproduced with cell wall components and have been shown to be potent inducers of cellular and humoral immunity. Among them, mannan and mannoprotein are found to be the ones with significant activities. Besides, they could also balance the enterobacteria, combine with the extrinsic pathogen, resist tumour, acted as an anti-oxidant agent.The mannan contents in different S. cerevisiae strains were compared in this study, results showed that the mannan content to each strain was different. The biomass of AKU 2.1424 was 905.02±9.91 mg/100ml, it was higher than other strains, and the mannan conent of AS 2.0016 was the highest. Freeze-dried samples of four S. cescerevisiae strains were subjected to spaceflight. After the satellite's landing on Earth, the samples were recovered and changes in yeast cell wall were analyzed. Spaceflight strains of all S. cerevisiae strains showed significant changes in cell wall thickness (p<0.05). One mutant of S. cerevisiae 2.0016 with increased biomass, cell wall thickness, and cell wall glucan was isolated (p <0.05). The spaceflight mutant of AS 2.0016 showed 46.69%, 62.62%, 18.82% and 146.87% increment in biomass, cell wall thickness, mannan andβ-glucan content, respectively, when compared to the ground strain.The mannan content of yeast must be influenced by culture medium and condition, so we optimized the fermentation condition. On the basis of the single factor experiment, the carbon and nitrogen sources and enzyme activator were determined, and then the mathematical model was established by the quadratic rotary combination design, through response surface analysis. The regression equation obtained for the mannan production is as follows:The optimized concentrations of culture medium were determined as 4.98 g/100 ml sucrose, 4.39 g/100 ml soybean peptone, 3.10 g/100 ml yeast extract and 2.21 g/100 ml glycerol. The optimized culture medium allowed mannan production to be increased from 85.72±3.38 mg/100 ml to 162.53±3.47 mg/100 ml. The influence of culture condition on mannan production was evaluated and confirmed by orthogonale experimental design, the optimized culture condition was: pH-5, inoculum size-5 ml, temperature-32oC and media volume-40 ml. The maximum mannan production enhanced 65.08% at the optimum culture condition.The processing conditions of hot water extraction and alkali extraction of mannan were optimized. The optimum condition for hot water extraction was composed of induced autolysis at pH 5.0, 3% NaCl, 55oC, 120 r/min and hot water treatment.at 120oC for 3 h. Besides that, the The optimum condition for alkali extraction was determined as: KOH 2%, 100 oC and treated for 2 h. TCA was selected to remove the freeprotein, after that, ethanol was used to precipitate the mannan. Finally, WSMP and ASMP were obtained at a yield of 6.42% and 5.93%, purity of 81.32% and 88.24% respectively.The physicochemical properties of WSMP an ASMP were studied. The average Mw of WSMP and ASMP were 1.81127×105 Da and 6.5098×104 Da, the weight-average molecular of WSMP and ASMP were 1.667×105 Da and 6.620×104 Da respectively. Both the polydispersity to each mannan were less than 1.5, that meaned the molecular mass with narrow distribution. HPLC analysis showed that mannan mainly consist of mannose. WSMP included 17 amino acid and the ratio of Ser, Thr and Asp were higher.β-elimination reaction, UV, amino acid analysis and GC analysis showed that the mannoprotein linked to oligosaccharides by O-linked and N-link oligosaccharides. The structure of mannan was analysed by FTIR and NMR specturm and determined as follows:By AFM, it was observed the netted texture of WSMP consisted by little round particles and existed as a aggregation, ASMP aggregated to rod-shaped. By SEM, the mannan appearance also showed glue-link and aggregation state.Effects of WSMP, WSM and ASMP on splenic lymphocyte transformation assay, delayed type hypersensitivity reaction and peritoneal macrophage phagocytizing chicken red blood cell assay were investigated in mice by immune-enhancing assay of animals. Results indicated that the WSMP, WSM and ASMP affected on on splenic lymphocyte transformation assay significantly (p<0.05). Delayed type hypersensitivity reaction was significantly enhanced when the mice were administered with WSMP, WSM and ASMP. Therefore, both WSMP, WSM and ASMP have immunization regulating function which could be judged, and overall evaluation was that the immune function of WSM and WSMP was stronger than that of ASMP. The WSMP and WSM had different degrees of inhibitory effects on HL-60, Eca-109 and HepG2 tumor cells in vitro.
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