Synergistic Interaction Of Mechanical Activation And Metal Salt On Strengthening The Saccharification Of Cassava Flour

Guangxi is the largest producer of cassava planting and processing in China,and cassava alcohol industry has great advantages in Guangxi.Nowadays,as the increased energy crisis,resource crisis and environmental deterioration,it is significant to make full use of cassava and processing products for the country and the world's renewable green energy development strategy and sustainable development.In order to solve the problems such as high energy consumption,high cost,complex process and energy wasting,the effects of mechanical activation(MA)and synergism of MA and metal salt pretreatments on the structural properties,accessibility and enzymatic hydrolysis activity of cassava starch and cassava flour were investigated in this paper,aiming to achieve direct saccharification of cassava feedstock without liquefaction,which could simplify the production process of cassava ethanol and reduce the production cost.(1)The synergistic effect of MA and metal salt(AlCl3)was investigated by the contrast of three pretreatment methods(MA,AIC13 and MA+AICl3)on the structural properties of cassava starch and cassava flour.The results show that the MA+AlCl3 synergetic pretreatment greatly reduced the viscosity of cassava starch and cassava flour,enhanced their thermal stability and weakened their gel properties.X-ray diffraction(XRD)results show that MA could destroy thecrystalline structure of cassava starch and cassava flour,leading to the decrease of their crystallinity,and the effect of MA+AICl3 pretreatment was more remarkable.Obviously,MA destroyed the particles of cassava starch and cassava flour,which can be observed by scanning electron microscopy(SEM).The surfaces of the particles were rough,twisted,and fracted,and the particles became smaller.The degree of damage of MA+AICl3 synergetic pretreatment was higher,and the grain refinement was more obvious.Fourier transform infrared spectroscopy(FTIR)results show that no new groups generated in cassava starch and cassava flour after different pretreatments.(2)Using cassava starch as raw material,AICl3 as additive,and dextrose equivalent(DE)of enzymatic hydrolysis as index,the effect of MA+metal salt pretreatment on the structural properties and saccharification of starch was investigated.The results show that MA+AICl3 pretreatment could enhance the saccharification and DE value of starch as comparing with MA pretreatment.The optimum conditions of starch pretreatment were MA time(tM)60 min and AICl3 dosage 3%.The optimum conditions of enzymatic hydrolysis were substrate concentration(S)=12 mg.mL-1,glucoamylase dosage(E)=50 U,and saccharification reaction time(tR)=60 min.Under these conditions,the DE values of MA and MA+AlCl3 pretreated starches were 79.33%and 87.09%,respectively.The iodine test results show that the degree of saccharification of MA pretreated starch was higher than that of the synergism of MA+AlCl3 pretreated one.Under industrial conditions(solid-liquid ratio=1:3,E=200 U/g,tR30 and 60 min),the MA pretreated starch was the colloidal coagulation without liquidity,which could not be saccharified.While the synergism of MA+AlCl3 pretreated starch had good liquidity,and the saccharification results were as follows:tR=30 min,DE=44.19%;tR=60 min,DE=50.51%.The results meet the requirements of industrial production of saccharification time=30?60 min and DE=40-60%.(3)Compared with cassava starch,cassava flour contains other components,such as fiber,fat,ash,protein,and so on.The combination of starch and fiber and other small molecule substances are intertwined,forming a compact structure of cassava flour,which make higher requirements for its saccharification.On the basis of the above research,the effect of MA+metal salt pretreatment on the structural properties and saccharification of cassava flour was studied using cassava flour as raw material,AlCl3 as additive,and DE value of enzymatic hydrolysis as index.The results show that MA+AlCl3 pretreatment could enhance the saccharification and DE value of cassava flour as comparing with MA pretreatment.The optimum conditions for the pretreatment of cassava flour were as follows:tM=60 min,AlCl3 dosage=5%,and the moisture content of cassava flour=25%.The optimum conditions of enzymatic hydrolysis were S=12 mg.mL-1,E=50 U,tR=60 min.Under these conditions,the DE values of MA and the synergism of MA+AlCl3 pretreated cassava flour were 82.15 and 95.69%,respectively.Compared with the results of starch,the DE value of cassava flour was higher,which may due to the increased dosage of AlCl3 and make better effect.In addition,the cellulose in cassava flour also may be saccharified after pretreatment,leading to the increase of DE value.The iodine test results show that the degree of saccharification of MA pretreated cassava flour was higher than that of the synergism of MA+AlCl3 pretreated one.Under industrial conditions(solid-liquid ratio=1:3,E=200 U/g,tR=30 and 60 min),the same results as the cassava starch,the MA pretreated cassava flour could not be saccharified.While the saccharification results of the synergism of MA+AlCl3 pretreated cassava flour were as follows:tR=30 min,DE=53.22%;tR=60 min,DE=59.23%.The results meet the requirements of industrial production of saccharification time=30?60 min and DE=40?60%.