Producing ergosterol from corn straw hydrolysates using Saccharomyces cerevisiae
Ergosterol is an economically important metabolite produced by Saccharomyces cerevisiae. In this study, the production of ergosterol by the strain using corn straw as an inexpensive carbon source was investigated. The total yield of ergosterol was determined by both the biomass and ergosterol content in yeast cells which depend not only on the hydrolyze condition, but also on the culture conditions. The corn straw hydrolyzing stability test result showed that the average content of reduction sugar (dextrose equivalent, DE) was 52.3% and the conversion efficiency of hemi-cellulose was 80.0%. Cultivation in 10 L bioreactor was carried out under the optimized corn straw hydrolysate medium. According to the fermentation stabilized experiment, the mean values of biomass and ergosterol average content were up to 8.5 gL-1 and 2.35%, respectively. Results on the stability of ergosterol content in yeast cell extraction solution, crystallize ergosterol productivity and the mean extraction yield values are shown to be 2.35, 2.05, 87.24%, respectively. Scanning electron microscope (SEM) was employed to observe the morphology of the as-product, the infrared furrier spectrometer (IR) was used to record the infrared spectrum of the ergosterol, and the X-ray diffractometer (XRD) was carried out to characterize its component and crystallite structure. Characterization analysis indicated that the ergosterol obtained by yeast from corn straw hydrolysates has achieved high purity, and could be used as one of the widely used feedstock for Vitamin D2.
Key words: Corn straw, ergosterol, hydrolyze, fermentation, characterization.