| Immunologically active glucans are (l→3)-β-D-linked glucose polymers that occur as a primary component in the cell walls of bacteria, fungi, cereals, mushrooms, seaweed or are secreted extracellularly by various fungi. Fungi are almost entirely multicellular, with yeast, Saccharomyces cerviseae, being a prominent unicellular fungus. S. cerviseae are surrounded by a tough, rigid cell wall. Cell walls are dynamic structures during normal cell expansion. β-Glucans are the conserved structure of cell wall, which are (l→3)-linked β-D-glucopyranan backbone with (1 →6)-β-branches.The beneficial effects of glucans have been attributed to modulation of immune function, increased bacterial clearance, increased bactericidal activity, and other nonspecific effects. One strain of S. cerevisiae FL1 screened from the nature, rather than commercial spent yeast, was selected as the starting fungus for β-D-glucan production as their cell walls were thick under transmission electron microscopy. Influences of environmental conditions and media components on S. cerevisiae FL1 biomass were evaluated in shake flasks. Results indicated that cells multiplied and sugar dropped quickly with μmax of approximate 0.51h-1; influences of temperature, nutrient usage and agitation on biomass were significant; a satisfactory biomass productivity was obtained under the, condition: 30℃, 8% (w/v) glucose, 4% (w/v) peptone, and agitation speed of 220 r/min, medium volumetric ratio of 30% (v/v). In addition, sucrose as well as ammonium sulfate could be utilized by S. cerevisiae FL1 to meet their requirement for nutrients while inoculation ratio, in the observed range, had negligible effect on biomass. Due to inherent drawbacks of the traditional single factor experimental design, response surface methodology was further employed to optimize the growth media for S. cerevisiae FL1. The relationship between biomass and nutrients was founded, which correlated experiment well with R2 of 0.997. It wasy = 9.8634 + 1.0066x1, -0.2782x2 +2.3718x3 + 0.3187x1x2 +1.1812x1x2 -0.1688x2x3 -0.2414x12 -0.0735x22 -1.0191x32, where x1, x2, x3, denoted the concentration of sucrose, ammonium sulfate and yeast extract, respectively. Analysis of variables indicated that sucrose, ammonium sulfateand yeast extract significantly influenced biomass density. Further mathematical analysis was conducted. From the contour plot of the fitted mode, yeast extract and sucrose had significant positive effects on S. cerevisiae FL1 biomass while ammonium sulfate had negative effect on the biomass.(l→3)-β-D-Glucan has received much attention from 1940s. Traditional method for preparing (l→3)-β-D-glucan from S. cerevisiae is based on the repeated extractions with acids and alkali. However, there are some drawbacks in this method, such as large amount of chemicals required, time consuming, many impurities and much wastewater produced. Herein, a novel method to extract (1→3)-β-D-glucan from S. cerevisiae cell wall was proposed, which was based on the combination of induced autolysis and subsequent oxidation of the autolysed cell by sodium hypochlorite to remove undesirable substances. Influences of temperature, pH value and organic solvent on S. cerevisiae FL1 autolysis were investigated. Results indicated that each factor had its significant effect on induced autolysis and the optimal condition was 52℃, pH5.5 and 1.5% (v/v) ethyl acetate. The kinetics behavior of yeast autolytic process under the optimized condition was further studied. After 36h of autolysis, 42.0% (w/w) cellular substances were released while cell wall nearly remained intact. Finally, an ideal glucan yield as high as 22.9% (w/w) was obtained when S. cerevisiae FL1 was treated with the novel method. Infrared spectrum and H NMR spectra conferred the prepared polysaccharide was (l→3)-β-D-glucan. However, the aqueous solubility of (l→3)-β-D-glucan was still poor.In biochemical process with whole cell used, S. cerviseae may encounter several environmental stresses that adversely affect c...
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