Influence Of Aqueous Ammonia Pretreatment On Dissolution And Enzymatic Hydrolysis Of Non-cellulosic Polysaccharides Around Cell Wall In Sugar Beet Pulp

As an important sugar crop,sugar beet(Beta vulgaris)is widely cultivated in the world.A large amount of waste generated by the planting and processing of sugar beet,which is regarded as the significant raw resource in biorefinery.Different organs or tissues exhibit remarkablely heterogeneity in chemical component,physical property and cell morphology.Mechanisms of the heterogeneity on enzymatic hydrolysis are generally complicated and ambiguous.The ambiguous mechanism severely impedes development of aqueous ammonia(AA)pretreatment in fuel ethanol production from sugar beet pulp.The differences of physical-chemical features of root,stem and leaf in sugar beet were discussed in this research.Additionally,the adsorption of cell wall to cellulase and the morphology variation during enzymatic hydrolysis were also observed.Variations of cell wall polymers and their impacts on enzymatic digestibility were analyzed multidimensionally,in terms of physical properties,wet chemistry compositions,glycome profiling and in situ immunolabeling during AA pretreatment at 80 ℃for 7 h.The main results are as follows:(1)The root and stem of sugar beet showed similar physical and chemical properties.Parenchyma cell in root,stem and leaf adsorbed more cellulase and were degraded more easily.The compiled data revealed that highly complicated physical-chemical properties of cell wall interface seemed to be a crucial factor that correlated to cellulase adsorption and further affected saccharification.(2)AA pretreatment removed the non-cellulosic polysaccharides,destroyed the rigid structure of cell wall,exposed cellulose hydroxyl groups and decreased the tissue texture.The crystallinity of SBP increased from 20.52%(0 h)to 37.55%(7 h).In addition,the physical and chemical properties of cellulose were changed and the accessibility was significantly improved.And the dense,orderly structure of cell wall was disturbed,reducing sugar yields ranging from 437.7 to 441.48mg/g were obtained from the P-SBP(3,5 and 7 h),which was increased by 87%than the control.(3)Non-cellulosic polysaccharides of the cell wall during the AA pretreatment performed various dissolution laws.Arabinogalactans and pectic compositions were easily deconstructed and dissolved,whereas,xylans and xyloglucans tended to be released.The dissolution of non-cellulosic glycans affected the physicochemical properties and enzymatic hydrolysis of sugar beet pulp.(4)Cell corner seemed to be the most resistant to enzyme digestion,which was even strengthened by the concomitant gathering of recalcitrant glycans.(5)The integration of glycans and their associations within cell walls played a larger role in recalcitrance.Xylan and pectin polysaccharides were the main recalcitrant glycans.Selecting a proper pretreatment to precisely destroy the vital glycan epitopes might be an economically feasible strategy.