| Increasing the initial concentration of corn starch slurry can reduce water and energy consumption in starch sugar production and cut the cost. However, the viscosity of starch paste increased during gelatinization and liquefaction when starch concentration increased to a certain degree. The system was difficult to stir and mix, which had bad effects on efficiency and products of liquefaction. In this study, the effects on the liquefaction of high concentration corn starch slurry adding compound enzyme were investigated. The detailed results were shown as follows.Firstly, the reaction system of high concentration corn starch slurry using compound enzyme was established. In this study, medium- temperature α-amylase and high-temperature α-amylase were chosen to liquefy starch slurry at high concentration. The medium-temperature α-amylase had certain effects on the slurry at first to decreasing the viscosity. The optimal conditions of medium-temperature α-amylase were studied and the detailed technologies were as follows: the corn starch was mixed with water at 60°C and the p H was 6.0. The medium-temperature α-amylase(0.075 U/g) and high- temperature α-amylase(14 U/g) were added into the system for 15 min before increasing to 90°C with the heating rate 1°C/min. The temperature of system was decreased to saccharification temperature to saccharify. Meanwhile, the effects of medium- temperature α-amylase on starch granules were investigated by SEM and XRD, which showed holes on the starch surfaces. This was contributed to the damaging of crystalline structures, resulting in the decrease of crystallinity and viscosity during the liquefaction.Secondly, the effects of compound enzyme on liquefaction process and products were studied compare to high-temperature α-amylase. The results showed that viscosity was reduced using compound enzyme during liquefaction and the DE value was increased and reaction time was decreased. The compound enzyme had little influence on liquefaction at low concentration but huge influence at high concentration. In addition, the effects of compound enzyme on liquefaction process were studied using GPC, HPLC, HPAEC-PAD and XRD methods. The results showed that average molecular weight and dispersion D value decreased during the liquefaction. Meanwhile, the molecular weight distribution of liquefaction products became more uniform and the amount of DP≤7 increased while that of DP>7 decreased. The average chain- length of liquefaction products was shortened, which indicated the crystallinity was decreased and the liquefaction process was complete.Finally, the effects of compound enzyme on saccharification process and products were studied compare to high-temperatureα-amylase using the glucose yield and b y-product generation rate as the index. DE value and enzyme amount were optimized in saccharification system as follows: DE value was 15, amount of glucose was 70 U/g, temperature was 60°C, p H was 4.5 and reaction time was 48 h. The effects of high concentration liquefaction on saccharification were studied. The results showed that the yield of glucose and by-product in the process when the liquefied liquid with higher concentration(45%, 40%, 35%) was diluted to 30% were similar to that of 30% liquefied liquid. The effects of compound enzyme on saccharification produces were studied. The results showed that glucose yield increased during saccharification and compound enzyme was beneficial to saccharification at high concentration. The effects of pullulanase on saccharification products were investigated. The results showed that pullulanase could increase glucose yield. The glucose yield of 45% high concentration slurry was 95.32%, nearly reaching that of 30% starch slurry saccharification. |
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