Optimization Of Fermentation Technology And Nutritional Value Of Spent Mushroom Substrates Of Pleurotus Eryngii By Solid-State Bacterium-Enzyme Cofermentation

The aim of this study was to screen out the natural strains that can efficiently degrade the neutral detergent fiber(NDF)of spent mushroom substrates of Pleurotus eryngii(SPES),as well as the complex enzymes that can efficiently hydrolyze SEPS and release reducing sugar.The solid-state bacterium-enzyme cofermentation(SSECF)process of SPES was optimized by response surface methodology(RSM),and nutritional value of SPES was evaluated.Exp.1 Screening of cellulose degrading strainsIn this experiment,18 normal strains were isolated from rumen fluid of cattle preserved in the laboratory.According to the results of preliminary screening and further screening test,three strains with strong cellulose degradation ability were found,that Strain GLY6-6 is Bacillus amyloliquefaciens,L6 is Bacillus subtilis,and NLG2 is Bacillus licheniformis.Their CMCase and FPase are 106.40 U/g,95.58 U/g,101.63 U/g,and 28.60 U/g,25.78 U/g and 28.24 U/g,respectively.Taking SPES as the sole carbon source,the single factor solid-stat fermentation experiment was carried out with three strains obtained from further screening.The results showed that L6 group has the best degradation rate of NDF compared with the other two strains.So Bacillus subtilis L6 was chosen for the following fermentation experiment with Lactobacillus plantarum and Saccharomyces cerevisiae.Exp.2 Study on solid state enzymatic hydrolysis of SPES with complex enzymeThe purpose of this experiment was to screen the combination of enzyme which can efficiently hydrolyze SPES from cellulase,xylanase,galactosidase,pectinase and mannanase,and the results showed that under the conditions of normal p H,60% moisture,20 h and 50 ℃,the release of reducing sugar was 210.89 mg/g,which was 10.37 times higher than that of the control group.Exp.3 Optimization of SSECF technology of SPES by bacteria and enzymeIn this experiment,Bacillus subtilis L6 and enzyme complex screened from Experiment 1 and Experiment 2 were used in solid-state fermentation with Lactobacillus plantarum and Saccharomyces cerevisiae.Plackett-Burman test and Box-Behnken test were designed to optimize the fermentation conditions by RSM,with the degradation rate of NDF as the response value,the best co-fermentation technology of SPES was determined as follow:Under the conditions of 10% inoculation of Bacillus subtilis L6,2% of Lactobacillus plantarum,2%of Saccharomyces cerevisiae,10% of cellulase,10% of xylanase,2% of β-galactosidase,1% urea,70 h,36.8 ℃ and 59% of moisture,the degradation rate of NDF was 23.69%.Exp.4 Evaluation of nutritional value of SPES by SSECFIn this experiment,simulated digestion system II(SDS-II)was used to digest SPES obtained from the optimal fermentation process in Experiment 3,and the simulated digestibility of dry matter(SDDM)and gross energy(SDGE)by two-step enzymatic method(simulated stomach and small intestine)was obtained.The results showed that the SDDM and SDGE of fermented SPES were both significantly higher than those of unfermented SPES(P < 0.05).In vivo results of metabolizable energy(ME)test showed that the AME and TME of FSPES increased by 2.44 MJ/kg and 2.65 MJ/kg,respectively.The apparent metabolizable rate and true metabolizable rate of DM of FSPES increased but the difference was not significant(P>0.05).