| In this study, a solid state fermentation (SSF) using single and complex microbial strains were conducted to improve the nutritional quality of cassava residue and the optimal fermentation parameters were investigated. And the objective of this study want to provide some theoretical basis for the exploitation and utilization of low quality non-conventional feed resources.Experiment 1:Nutritional improvement of cassava residue by solid-state fermentation with single microbial strainThe purpose of this experiment was to investigate the effect of SSF with single microbial strain on nutritional quality improvement of cassava residue, and the optimal fermentation parameters were investigated. Firstly, Aspergillus Niger-Ⅱ with best fermentaion effect was screened from 12 strains. Then, Single factor experiment design was adopted to investigate the effects of fungi inoculation size, rapeseed meal ration, fermentation time, temperature, moisture and initial pH on the fermentation of cassava residue; Orthogonal experiment design was further adopted to optimize the fermentation parameters (such as fermentation time, fermentation temperature, moisture and initial pH) on nutritional quality improvement of cassava residue.The results showed as following:(1) Inoculated 3×106spergillus niger-Ⅱ spore per gram fermentation materials, added 15% rapeseed meal (rapeseed meal:cassava residue ratio), controlled the ratio of substrate vs water ratio to 1:1.5 and fermented with initial pH 4 at 36℃ for 4 days can get a optimal result. (2) Fermented cassava residue under the optimized condition described above and calculated base on dry matter (DM), the crude fiber was significantly decreased from 22.26% to 17.71 (P<0.05) and the reducing sugar was increased from 1.42% to 5.11% (P<0.05), crude protein was increased from 8.67% to 13.48% (P<0.05), crude fat was increased from 7.89% to 11.72%(P<0.05), the ash was increased from 6.02% to 7.31% (P<0.05), Moreover, the enzyme activity of CMCase, FPA, B-Glucosidase reached to 9.05U,2.37U,2.35U per gram dry matter after SSF, respectively.Experiment 2:Nutritional improvement of cassava residue by solid-state fermentation with complex microbial strainsThe purpose of this experiment was to investigate the effect of SSF with complex microbial strains on nutritional quality improvement of cassava residue, and the optimal fermentation parameters were investigated. Firstly, According to the results of single microbial strain screening in experiment 1, four single microbial strains (Aspergillus Niger-Ⅱ, Trichoderma viride, Bacillus subtilis-Ⅱ and Saccharomyces cerevisiae) with best fermentation effect were screened from 12 strains and four species of microbe; Then the optimal experiment for microbial strains formulation were conduct and the results showed that the combination of Aspergillus niger-Ⅱ1, Bacillus subtilis-Ⅱ and Saccharomyces cerevisiae showed a higher CMCase enzyme activity, CP% and reducing sugar improvement after SSF than other combinations; and the optimaized inoculation proportion for Aspergillus niger-Ⅱ: Bacillus subtilis-Ⅱ: Saccharomyces cerevisiae were 3:2:1, and the best inoculation size was 2.5×106 erm/g fermentation substrate. Then, Single factor experiment design was adopted to investigate the effects of rapeseed meal ration, fermentation time, temperature, moisture and initial pH fermentation of cassava residue by above screened complex microbial strains; orthogonal experiment design was further used to optimize the fermentation parameters (such as fermentation time, fermentation temperature, moisture and initial pH) on nutritional quality improvement of cassava residue.Finally, the optimied parameters of complex microbial strains fermentation was obtained as follows:Inoculated 2.5×10of Aspergillus niger-Ⅱ spore, Bacillus subtilis-Ⅱ and Saccharomyces cerevisiae at the ratio of 3:2:1 per gram fermentation materials, added 20% rapeseed meal (rapeseed meal:cassava residue ratio), controlled the ratio of substrate vs water to 1:2 and fermented with initial pH 4 at 35℃ for 4 days. Fermented cassava residue under the optimized condition described above and calculated base on dry matter, the crude fiber was significantly decreased from 21.50% to 16.54 (P<005) and the reducing sugar was increased from 1.14% to 2.20% (P<005), crude protein was increased from 10.77% to 17.92%(P<005), crude fat was increased from 8.17% to 12.60% (P<005), the ash was increased from 6.13% to 8.62%(P<0.05). Moreover, the enzyme activity of CMCase, FPA, B-Glucosidase reached to 12.31U,3.92U,3.95U per gram dry matter after SSF, respectively.Cassava residue fermented with single Aspergillus niger-Ⅱ strain, the CP has a improvement of 4.81% and reducing sugar was increased by 3.69%, while the CF decreased by 4.56% after SSF; When fermented with complex microbial strains, the CP increased by 7.15%, reducing sugar increased by 1.06% and the CF decreased by 4.96% after SSF. Also, complex microbial strains fermentation has a higher cellulase activity, such as CMCase, FPA, β-Glucosidase than Aspergillus niger-Ⅱ strain. In conclusion, Complex microbial strains showed a better nutritional improvement of cassava residue after SSF than those of single microbial strain fermentation (Aspergillus niger-Ⅱ). |
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