Technical Study On Co-Degradation Of Corn Stalk And Its Feed Transformation By Enzymes And Microorganisms

The annual yield of crop stalk reaches 700 million tons in our country, and corn stalk is 200 million tons. A large amount of crop stalk has not been utilized effectively. The result has been that not only natural resources are wasted, but also environment pollution is induced. Bioconversion of corn stalk into monosaccharide to produce protein feed or other fermentation products is an effective approach to achieve full utilization of renewable resources. This will be helpful in solving the crisis of foodstuff inadequacy and energy. And also reduce environmental pollution, adjustment the structure of agriculture, so that achieve comprehensive utilization of resource and promote sustainable development of agriculture.The purpose of this study was to produce protein feed. Corn stalk was treated by physical method and then was converted to produce protein feed by biotechnology. The ways of the study were:Cell walls'complex structures of corn stalk were destroyed by thermophilic digestion and were easier to be hydrolyzed by enzymes. Then, various kinds of polyglucoses were degraded to monosaccharide by complex enzymes. Finally, converted to mycoprotein in the way of both strains fermentation and the protein content of stalk increased. The results were got as follows:1. Fermenting sugar mixture to produce protein feed by both strains was optimized. The medium(g/L) was:glucose 60, xylose 40, (NH4)2SO4 21.0, urea 6.0, yeast powder 4.0, MgSO4 1.1, K2HPO4 1.0, KH2PO4 1.0. Utilization rate of xylose, utilization rate of glucose, yield of dried yeast and yield of yeast protein was 91.65%,92.39%,18.22g/L and 9.30g/L respectively when the conditions were:liquid-installed of 250mL conical flask 100mL, inoculum size of candida utilis 4%, inoculum size of pachysolen tannophilus 6%, rotate speed 160r/min, temperature 30℃and time 18h. The result shows that it is varibe to produce mycoprotein by using xylose and glucose as cabon source.2. Thermophilic digestion preprocessing conditions of corn stalk were optimized. Original stalk, of which mesh and percentage of moisture were 40 and 7.94% respectively, was steamed at 180℃for 1.5h in the high-temperature cooking pot. The comparison of enzymatic hydrolysis showed that degradation rates of steamed stalk and orignal stalk were 72.20% and 48.50% respectively. The difference of enzymatic effect was significant between each other. And degradation rate of steamed stalk is very close to theory degradation rate. The result shows enzymatic effect of corn stalk is improved greatly by thermophilic digestion preprocessing method.3. The complex enzymes zymolysis conditions of steamed stalk was optimized.3.072g steamed stalk was put in 30mL citrate buffer solution (pH4.8) and adjusted pH4.8 before pasteurization at 121℃for 20 min. Then put into 87.5U cellulase,100U xylanase,60Uβ-glucanase and 39U pectase after cooling down. Finally, the yield of reducing sugar was 0.8940g (pentose was 0.4583g) under the conditions of rotate speed 100r/min, temperature 50℃and time 16h. And it was no influence of enzymatic effect as mixing with yeast fermentation nutrients which was needed. The result shows that complex enzymes'enzymatic effect is remarkable in the beginning period, but they would be restrained when the reducing sugar achieves a certain concentration.4. The conditions of simultaneous saccharification and fermentation of stalk to produce protein feed using both strains was optimized. Steamed stalk 3.072g was mixed with ammonium sulfate 0.25g, urea 0.10g, yeast powder 0.06g, magnesium sulphate 0.010g and pH 4.8 citrate buffer solution 30mL. And adjusted pH4.8 before pasteurization at 121℃for 20min. Then degraded for 16h by complex enzymes in their optimal conditions. Then inoculated Candida utilis 2.0mL and Pachysolen tannophilus 2.0mL in them and fermented for 55h under the conditions of temperature 29℃and rotate speed 100r/min. Finally, gained fermentation stalk 3.021g, crude protein feed 0.8591g and the content of crude protein 28.44% which is 4.33 times of oven dry one's. The result shows that the content of stalk's crude protein increases significantly by bioconversion and is more than 20% which is the lowest crude protein content requirement of protein feed. The technology for producing protein feed is non pollution, less enzymes and significant degradation effect, in which stalk is treated by thermophilic digestion and degraded by enzymes and microorganisms. The technology has extensive reference value for transforming corn stalk to protein feed.