| With the exhausting of fossil-fuel resources and environmental deterioration, it is essential to develop some alternative fuels. Bio-energy is one form of the solar energy, which is regarded as clean and environmental friendly. Above all, bio-ethanol is the most promising one. Sweet sorghum [Sorghum bicolor (L.) Moench] is a C4plant characterized by a high photosynthetic efficiency. Its resistance to drought, salinity and water-logging characterize it as one of the best feedstock for ethanol production. However, one of the bottleneck problems for the ethanol production from sweet sorghum is the high capital cost. Therefore, developing high added value by-products is one of the effective way to reduce ethanol production cost.The concentrated stalk juice of "TE706" sweet sorghum variety was used to produce bio-ethanol and yeast SOD (Superoxide dismutase). The experiments were carried out at35℃and150rpm. Eleven different parameters (including C, N, P, metal ions and vitamins) were investigated to clarify their effects on ethanol yield and yeast SOD production. Meanwhile, the optimization of three main factors was also performed by response surface method (RSM). The results showed that the effects of initial sugar concentration, inoculation concentration,(NH4)2SO4, K2HPO4, CUSO4, thiamine and inositol on ethanol yield and yeast biomass were significant. The effects of CaCl2, Zn(AC)2, Niacin on ethanol yield and CaCl2, MgSO4on yeast biomass were not significant. In addition, all the factors significantly influenced yeast SOD production. With the increase of initial sugar concentration,(NH4)2SO4, K2HPO4, MgSO4, CUSO4, Zn(AC)2, thiamine and inositol adding concentration, it could obtain a peak value of ethanol yield. However, an adverse effect on ethanol fermentation was caused as a rising of CaCl2, Niacin and inoculation concentration. Suitable concentration of initial sugar, inoculation quantity,(NH4)2SO4, K2HPO4, CUSO4, Zn(AC)2, thiamine and inositol were propitious to biomass synthesis. Whereas, CaCl2, MgSO4and niacin gave an opposite effect on yeast biomass. There was a minimum value of yeast SOD production with the increase of (NH4)2SO4, CUSO4, Zn(AC)2, thiamine and inositol concentration. Nevertheless, the increase of CaCl2, MgSO4and initial sugar concentration could bring a maximum of yeast SOD production. By contrast to the constantly stimulatory effect on yeast SOD production of K2HPO4, increase of inoculation concentration would decrease the yeast SOD production. Suitable initial sugar, inoculation,(NH4)2SO4,K2HPO4, CUSO4, Zn(AC)2and thiamine concentration could increase the maximum CO2weight loss. Above all, increasing of initial sugar concentration resulted in a longer fermentation time. On the other hand,(NH4)2SO4and thiamine could reduce fermentation time with a higher maximum CO2weight loss. It means that (NH4)2SO4and thiamine enhanced fermentation efficiency and fermentation speed. It was found that the effects of (NH4)2SO4, K2HPO4and inositol on both ethanol yield and yeast SOD production were most significant based on the one factor experiment. Optimization of mentioned three parameters was attempted by response surface methodology based on Box-Behnken design for the optimal production of ethanol and yeast SOD. According to the results, the influence sequence of the tree parameters on ethanol yield was K.2HPO4>(NH4)2SO4> inositol, while for the yeast SOD production, the influence sequence was (NH4)2SO4> K2HPO4> inositol. According to the integrated balance, a suitable and comprising fermentation condition for both ethanol yield and yeast SOD production could be set as (NH4)2SO4of0.00g/L, K2HPO4of1.53g/L and inositol of63.37mg/L. At the optimum conditions, ethanol yield of81.34%and yeast SOD production of3.03X104U/Lwere obtained.In summary, the effects of eleven factors on ethanol yield and yeast SOD and a comprising optimum fermentation condition were obtained. Considerable amount of yeast SOD production was obtained based on a relative high ethanol yield. |
