Study On The Technological Conditions For Producing Cassava Fuel Alcohol By Very-Hige-Gravity Fermentation

In recent years, research on alcohol production has focused on very high gravity fermentation (VHGF). It can increase plant capacity and efficiency, decrease the labor costs and the consumption of energy, and relieve the load of potale's disposal. VHGF has a bright applying future. According to the development of the cassava industry in Guangxi municipality, producing cassava alcohol was studied by high-gravity fermentation in this paper, and the four main aspects of work and its results were finished.In order to decrease the viscosity and ameliorate the effect of liquefaction in the high-gravity fermentation, the technological conditions of liquefaction were studied. Based on analyzing the character of liquefaction enzyme and the curve of viscosity in liquefaction, the technological conditions of liquefaction have been studied via single factor and orthogonal experiments. Finally the optimum liquefaction conditions found as follows: the suitable particle size of cassava was 0.42 mm, the ratio of cassava and water(60℃) was 1:2.3, the dosage of liquefaction enzyme was 10u/g , preheated at 60℃for 30 min, then liquefied at 105℃for 2 hours. After the liquefaction, the cassava starch was liquefied completely. The viscosity dropped largely, less than 10% viscosity of liquefaction without liquefaction enzyme.Based on the above optimum condition, the technological conditions of saccharification were obtained by analyzing the activity and stability of saccharification enzyme. And the technological conditions of saccharification have been studied via single factor experiment, such as saccharification pH, temperature, time and the dosage of saccharification enzyme. Finally the optimum working conditions was found for saccharification via orthogonal experiments: saccharification pH4.5, saccharification enzyme added 150 u/g cassava when the liquefaction liquor was cooled to 60℃, the saccharification time was 30 min while the saccharification liquor cooling from 60℃to 33℃.It was studied that the experimental technology and conditions of the alcohol fermentation using cassava by very-high-gravity fermentation based on the above optimum condition. Fermentation conditions have been studied, such as fermentation temperature, pH, and nitrogen adding, and so on. The conditions of fermentation and the need of nutrition salts in fermentation substrate have been studied via orthogonal experiments. According to the experimental results: the optimum temperature of alcohol fermentation was 33℃, the initial pH of fermentation was 4.5, the amount of inoculation of yeast was 10% (v/v), the time of fermentation was 48 h, 80 r/min shaker. The need of nutrition salts in fermentation substrate was: MgSO₄·7H₂O (0.45 g/L), urea (0.25 g/100g cassava flour), KH₂PO₄(1.5 g/L), CaCl₂ (0.2 g/L). After the fermentation, 15.7% (v/v) alcohol was got with 92.8% starch utilization rate in 500mL triangle bottle. After three-parallel fermentation, 15.63% (v/v) alcohol was got with above 92% starch utilization rate in 500mL triangle bottle.Fermentation conditions of 5 L,100 L bioreactor has been studied based on the above optimum condition. 33℃fermented for 48 h, after the fermentation, 15.3 %(v/v) alcohol was got with below 0.3 g/100mL residue total sugar and 92.02% starch utilization in 5 L bioreactor; 15.1 % (v/v) alcohol was got with below 0.5 g/100mL residue total sugar and 91.06% starch utilization in 100 L bioreactor. This technological is useful to apply in industry.