Aqueous Ammonia Pretreatment Facilitated Cellulose Enzymatic Digestibility Of Caragana Through Deconstruct Cell Wall

As an ecological plant,Caragana is widely planted in arid and semi-arid regions.High-value utilization of Caragana is great significance to the sustainable development of deserticulture.However,the immaturity of transformation and processing system significantly hampered the sustainable development of Caragana ecological industry.In this study,Caragana was pretreated by aqueous ammonia to improve its cellulase enzymatic digestibility.First,the digestibility of stem and leaf of four species of Caragana were compared.Additionally,the stem of Caragana was pretreated with aqueous ammonia at different temperatures.And the effects of aqueous ammonia pretreatment on the wet chemistry composition,physical properties,microstructure and enzymatic hydrolysis were investigated.The effects of aqueous ammonia pretreatment on cell wall crosslinking structure and glycan epitopes of Caragana were further analyzed by the fourier transform infrared,glycome profiling and in situ immunolabeling.The main results are as follows:(1)The graded utilization is an effective means for high valued utilization of Caragana.The leaf and thin stem(diameter lower than 0.5 cm)of Caragana exhibited excellent forage quality,whereas,the medium and thick stem(diameter greater than 0.5 cm)with high lignifications should be pretreated to improve its enzymatic digestibility.(2)Aqueous ammonia pretreatment can degrade hemicelluloses and neutral detergent soluble,retain cellulose,explicitly eliminate non-cellulosic cell wall glycan epitopes e.g.pectin/arabinogalactan epitopes,and break ester bond,ether bond and hydrogen bond in the crosslinking structure of lignin carbohydrate complex to destroy the integrity of the cell wall.(3)With the destruction of chemical structure and the dissolution of polysaccharide from cell wall by aqueous ammonia,the compact structure of Caragana was destroyed,and the porosity increased,and the cellulose crystalline region exposed,and the cellulose accessibility increased.(4)After aqueous ammonia pretreatment,the adsorption of cellulase on Caragana cell wall enhanced and the reducing sugar yield of Caragana significantly increased.The optimal reducing sugar yield of the pretreated Caragana(80℃)could reach 316.93 mg/g,which is 1.61 times higher than that of the control.In conclusion,the aqueous ammonia pretreatment at atmospheric temperature can effectively change the physicochemical structure and destroy the cell wall crosslinking structure of Caragana,which is a promising strategy to destroy recalcitrance for cellulase digestibility of Caragana.