| In the current production process of starch sugars, the low initial concentrations of starch result in large heat energy consumption. In order to reduce the cost of starch sugars, one of the most effective ways is to improve the initial concentrations of starch slurry. However, the viscosity of starch emulsion increases with the increasing of the initial concentrations in the gelatinization of corn starch. Therefore, it is imperative to solve the problem about high viscosity of corn starch at high concentrations. Granule starch hydrolyzing enzyme(GSHE) can be used to hydrolyze raw starch granules directly, and could be used in the production of starch sugars. In this study, GSHE was used as catalyst, and the system of hydrolyzing corn starch at high concentrations with GSHE was established and the influences of initial concentrations of corn starch slurry in hydrolysis process were studied. Then, two-step hydrolysis improved the glucose yields at high concentrations of corn starch, the collaborative reaction(two-step hydrolysis and calcium) improved efficiency of hydrolyzing corn starch at high concentrations with GSHE further. Finally, the system was applied to product starch sugars and compared with traditional processes. It provided a new way to product starch sugar in the experiments.The main contents are attached as follows:(1) The system of hydrolyzing corn starch at high concentrations with GSHE was established. Using glucose yields and glucose values(DE values) as the indexes, enzyme concentrations, time, temperature and p H were optimized, then, the effects of hydrolyzing different initial concentration of corn starch with GSHE were studied. The results were as follows: we choose different concentrations of corn starch slurries in 65℃ and 55℃, adjusted the p H to 4.0, then added 50 U/g GSHE for 2 h. Glucose yields and DE values were declined with the increasing of concentration of starch by 8.38% and 10.26% for 45% and 41.27% and 45.10% for 50%, respectively.Its mechanisms were analyzed using Brabender, Nuclear Magnetic Resonance(NMR), etc. The results were as: with the increase of the concentrations of starch slurries, the gelatinization viscosity increased, water molecule mobility reduced, which is harmful to improve the efficiency. As a result, glucose yields and DE values were declined obviously.(2) In order to improve glucose yields and DE values, a two-step hydrolysis of corn starch at high concentrations(45% and 50%, w/w) using GSHE was investigated and the mechanisms were studied. The results showed that the two-step hydrolysis(for 45%, reaction at 65℃ for 30 min, followed by reaction at 70℃ for 90 min, for 50%, reaction at 55℃ for 30min, followed by reaction at 65℃ for 90min) was more effective than a single-step hydrolysis involving reaction, the glucose contents and DE values increased by 15.52% and 13.01% for 45% starch slurry, and by 24.59% and 18.66% for 50% starch slurry. Its mechanisms were analyzed using Nuclear Magnetic Resonance(NMR), X-ray diffraction(XRD), etc. The peak viscosities of starch slurries were decreased by 23.80% and 28.30% with the two-step hydrolysis, respectively. The mobility of water increased. Thus, the two-step hydrolysis offers great advantages in the production of syrups using GSHE.(3) To improve the glucose yields further, adding 160mg/L calcium in the two-step hydrolysis. The mechanisms were measured by High Performance Liquid Chromatography(HPLC). The results showed that the glucose yields and DE values increased by 16.55% and 10.57% for 45% starch slurry, the glucose yields and DE values increased by 29.49% and 14.02% for 50% starch slurry.(4) After hydrolyzing 45% and 50% corn starch slurry using GSHE, the system was saccharified for starch sugar. Analyzed the process through the HPAEC-PAD and HPLC, the results showed that the molar mass distribution, compositions and contents of products were not change obviously, which showed the effects of pasting on enzymatic hydrolysis products was small. For the ultimate products, saccharification efficiency and the yields were reduced with the increasing of concentration. Two-step hydrolysis can improve product yields by 6.70% and 7.20%,respectively. Collaborative reaction can also further improve the glucose yields by 6.96% and 8.42%, respectively. Moreover, the sugar yields were 98.78% for 30% starch slurry, and 96.87% for 45% starch slurry. The by-product contents dropped significantly. It meet the industrial requirements and simplified the process, and showed great advantages than traditional processes. |
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