Compositional Features And Oxidative Depolymarization Of Spent Auricularia Auricular Substrate

China is a large edible mushroom producing country,with an annual output of 20 million tons of spend substrate（SS）,but the utilization of SS has not been effectively resolved for a long time.The shortcomings such as high moisture content,high heavy metal content,and extremely easy to breed molds have seriously hindered the development and utilization of SS.If it can be used as a chemical raw material to obtain high value-added oxygenated chemicals（OCs）,it has great application prospects.Detailed studying the composition and structure of organic matters in SS at the molecular level is crucial to the efficient utilization of SS.On this basis,the key to effective utilization of SS is developing conversion reactions which can break some covalent bonds in SS under mild conditions and selectively produce small-molecular organic compounds.In this study,composition and structure of organic matters in spend auricularia auricular substrate（SAAS）were performed using a two-step degradation,including sequential supercritical CO₂fluid extraction and sequential aqueous hydrogen peroxide/acetic anhydride（AHPO/AAH）mild oxidation,combined with various analytical techniques.The related model compounds,standards,and supercritical fluid extraction residues from SAAS(ER_SAAS)were used to study the oxidation mechanism and course,the polyamide column chromatography separation of soluble portions（SPs）was studied in order to develop promising approaches for obtaining OCs from SS.The formulation materials of SAAS—oak wood sawdust（OWSD）and wheat bran（WB）were also subjected to a two-step degradation method combining extraction and oxidation.We hope that the composition and structure of SAAS can be better understood through comparison.FTIR,XRPES,and SEM were used to directly characterize organic functional groups,surface element forms,and microstructural features in SAAS,OWSD,and WB.The results show that they contain functional groups such as hydroxyl,methyl（methylene）,O-glycosidic bonds,and carbonyl groups.The surface O and N are mainly C-O-,C-OH,C=O,amino nitrogen,amino nitrogen,pyrrole,and other forms exist.Almost all of the organic matters in SAAS,OWSD,and WB was converted into soluble organic species via the two-step degradation.High permeability supercritical CO₂fluid with petroleum ether（30-60 ^oC）,carbon disulfide,methanol,acetone and isometric acetone/carbon disulfide mixed solvent permeated into the interior of biomass,small molecular compounds that are free inside the biomass or bound by weak non-covalent bonds were released.The total extraction yield was 12.3%,15.6%,and 19.8%,respectively,the highest yield was the methanol-assisted extraction.The mild oxidation of AHPO/AAH can destroy the-C-O-bridge bonds in biomass,and it act on aromatic carbon to destroy the aromatic ring.The total degradation yield of SAAS,OWSD and WB extraction residues was 89.1%,79.7%,and81.5%,degradation occurred mainly in the first stage.Gas chromatography mass spectrometry technology detected 657 compounds in extracts and SPs,which can be classified into alkanes,alkenes,arenes,alcohols,phenols,aldehydes,ketones,esters,carboxylic acids（CAs）,monosaccharides and glycosides（M&Gs）,and nitrogen-containing organic compounds,sulfur-containing organic compound,and furan compounds.n-alkanes,alcohols,and esters are the most predominant in the extracts.N and S exist in various forms.The main components in SPs are CAs,and there are also a small amount of alcohols,ketones,M&Gs.By analyzing the composition of extracts and SPs,and combining the analyses with FTIRS and XRPES,it can be inferred that SAAS composition is rich in C₁₅-C₃₈alkanes,C₁₆-C₂₅aliphatic alkanols and alkanoates,and a small amount of free components such as arenes with 3-4 benzene rings,phenols,aldehydes and ketones.The hemicellulose in the skeleton structure of SAAS consists of D-ribose,rhamnose,arabinose,glucose,fructose,talose,and mannose,while the lignin is composed of guaiacyl,syringyl and from（-（CH₂）_n-,n=2-4）linked benzene ring structure,cellulose is composed ofβ-D glucopyranose.The oxidation of related model compounds shows that AHPO/AAH oxidant can break d-xylose monomerr ring opening and C-C bond cleavage,destroy the aromatic ring structure of guaiacol,and even destroy the fused ring of phenanthrene and fluoranthrene,the final results are small-molecular CAs.The degradation yield of cellulose,hemicellulose and lignin standards was8.3%,98.6%and 82.1%,respectively.Degradation of cellulose and hemicellulose can result in the ether bond being broken,monosaccharides ring opening,re-cycling or cleavage to produce alcohols,furanones,pyranones,aliphatic carboxylic acids.It is worth noting that the oligosaccharides produced by cellulose degradation have direct ring opening,C-C bond cleavage,and rearrangement reactions to produce ACAs with C₇-C₁₂.AHPO/AAH can selectively degrade the aromatic ring of lignin,not only obtain the monobasic aliphatic carboxylic acids from the aromatic ring side chain,but also the inter-aromatic ring-（CH₂）_n-linked binary aliphatic carboxylic acids and ternary aliphatic carboxylic acid,can even oxidize the benzene ring structure to generate a series of aromatic acids.The analysis of the compounds of the oxidation products which were taken out in different time showed that the skeleton structure of ER_SAASwas degraded in the order of side chain,hemicellulose,lignin and cellulose,the degradation process is accompanied by decomposition,polymerization and cyclization of the degradation products.AHPO/AAH oxidatively degraded biomass to obtain higher yield of OCs.However,the compounds contained in OCs were complex and had lower relative contents,so subsequent separation and purification are the key technology for obtaining high value-added OCs from biomass.The polyamide column chromatography separation technology was used to separate SPs of the full-component SAAS（FCSPs）.FCSPs was sequentially eluted with petroleum ether,petroleum ether/carbon disulfide mixed solvents with increased carbon disulfide to petroleum ether ratio,carbon disulfide,carbon disulfide/ethyl acetate mixed solvents with increased ethyl acetate to carbon disulfide ratio,and ethyl acetate,and 2-acetoxy-3-hydroxysuccinic acid,ribitol,tartaric acid,dihydro-2,5-furandione,2-methyl-2-acrylicacid-1,2-ethanedicarboxylate,succinic acid,and acetoxyacetic acid were finely separated in the FSPs.The feasibility of preparing OCs by mild transformation was further verified.This thesis contains 137 figures,46 tables,and 248 references.