| In this study, a solid state fermentation (SSF) using single and complex microbial strains were conducted to improve the nutritional quality of byproduct Sweet potato residue and the optimal fermentation parameters were investigated. Sweet potato residue and rapeseed meal were mixed with a ratio of 9:1 and fermented under different conditions, and the crude protein,CMCase activity and reducing sugar content after fermentation were investigated. Firstly, four single microbial strains with best fermentation effect were screened from 4 species,12 strains of microbe,and the strain with best nutritional improvement after fermentation was selected as the main fermentation strain and make different formulate with other three kind of strain screened for SSF. Then, Single factor experiment design was adopted to investigate the effects of inoculation size,fermentation time, the ratio of water and temperature on the fermentation of sweet potato residue by the single microbial strain,and the fermentation parameters were optimized. Also the best combination of the strains and their optimal ratio were investigated. Then a further orthogonal experiment design L16(45) was adopted to optimize the fermentation parameters by complex microbial strains.Finally the nutritional content, reducing sugar and enzyme activity of the sweet potato residue were compared after SSF under the optimized condition by single strain or complex microbial strain. Results are as following:1. According to the results of single microbial strain screening experiments, four single microbial strains (Aspergillus Niger 2 in Tspergillus, Trichoderma reese in Trichoderma, Bacillus subtilis 1 in Bacillus and Saccharomyces cerevisiae 1 in Yeast) with best fermentation effect were screened from 4 species,12 strains of microbe, and the Aspergillus Niger 2 was screened as the main fermentation strain.2. The optimizied fermentation parameters for Aspergillus Niger 2 dertrmined by single factor experiment were as following:inoculation size of 5×105 spore per gram fermentation material, fermentation time of 3.5 d, substrate and water ratio of 1:1.5, and fermentation temperature of 36℃.3. The optimizied fermentation parameters for Aspergillus Niger 2 dertrmined by orthogonal experiment design L9(34) were:inoculation size is 1×106 spore per gram fermentation material,fermentation time of 4 d, substrate and water ratio of 1:1.3, and fermentation temperature of 38℃. Fermented Sweet potato residue under the optimized condition described above and calculated base on dry matter (DM), crude protein was increased from 6.67% to 9.14%(P<0.05), improved by 43%; crude fat was increased from 2.71% to 4.75%(P<0.05), improved by 75%; the reducing sugar reached 7.34%. Moreover, the enzyme activity of CMCase activity, FPA,β-Glucosidase and amylase reached to 3.12,2.45,2.13 and 3.02 U per gram dry matter after SSF respectively.4.The combination of Aspergillus Niger 2, Trichoderma reese, Bacillus subtilis 1 and Saccharomyces cerevisiae 1 get the highest Crude protein improvement, followed by the combination of Aspergillus Niger 2, Trichoderma reese and Bacillus subtilis 1, but their have no significant difference between those two combination(P>0.05); the combinations of four microbial strains also showed the higher CMCase activity than other seven strain combination (P<0.05).5. The optimizied fermentation parameters for comlex microbial strain determined by orthogonal experiment design L16(45) were:Inoculated 1×106 germ/g fermentation substrate of Aspergillus Niger 2:Trichoderma reese:Bacillus subtilis 1:Saccharomyces cerevisiae 1 at the ratio of 1:1:2:1, controlled the ratio of substrate vs water ratio to 1:1.3 and fermented at 38℃ for 4.5 days. Fermented Sweet potato residue under the optimized condition described above and calculated base on dry matter (DM), crude protein was increased from 6.37% to 9.75%(P<0.05),improved 53%; crude fat was increased from 2.71% to 4.92%(P<0.05), improved 82%; the reducing sugar reached 8.22%; Moreover, the CMCase activity, FPA, B-Glucosidase and amylase reached to 4.26,3.29,3.75 and 5.15U per gram dry matter after SSF respectively.In conclusion, solid state fermentation (SSF) using single and complex microbial strains can improve the nutritional value of byproduct sweet potato residue and improve crude protein and crude fat content, also after fermentation there generated some enzymes such as CMCase, FPA,13-Glucosidase and amylase,which were benefical for the digestion and absorption of feed in animal. Complex microbial strains showed a better nutritional improvement of sweet potato residue after SSF than those of single microbial strain fermentation (Aspergillus niger). |
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