Screening Of Neutral Protease-producing Strain And Its Application In Corn Steeping Technology

In corn starch production, soaking corn is important which effects the output and quality of corn starch directly. In traditional corn wet method process sulfurous acid was used as soaking, which can break reticular formation of protein, enhanced permeability of corn epidermis, passivation germ, anticorrosion, and help to form lactic acid. But high-concentration sulfurous acid can bring on environmental pollution, etching apparatus,soaking time long, throughput of water large. As the critical process of corn wet method process, it effects the output and quality of corn starch directly.In this thesis based on the traditional wet processing technology for production of corn starch, using the properties of degradation of proteins by proteinases, accepted improved method of production of corn starch in laboratory, to extract microorganism from soak water of corn and corn steep liquor by selective medium, which could degrade proteins, enwrap corn starch in the neutral and acidic medium, and added it to the soak water of corn.The soak water of corn from factory is acidic, if add alkaline protease we need to incessantly adjust pH of soak solution. Therefor the purpose of this paper is to find strain from soak water of corn and corn steep liquor, which could produce high-yield protease in the neutral and acidic medium. The thesis has too much fact meaning for processing industry of corn.Because the strain of natural selection was low activity, mutagenic treatment strain, improving protease production is necessary. Then extract enzyme and measuremented enzyme properties. Finally, add fermentation liquid to corn soak solution. Make sure of the soaking effect, decreased concentration of sulfurous acid in corn soak solution, shortened the soaking time.1. Extract strainY7.0 from soak water of corn , producing neutral protease. Preliminary identificate this strain belongs to bacillus, Strains of Gram-positive. Systematically. Study on growth curve of strainY7.0, protease activity, amylase activity. The results showed that: strainY7.0 at pH7.0, 37℃, cultured 6h, entered in logarithmic growth phase, after 14h entered in terminal logarithmic growth phase. Ptotease activity of this strain is high, and not to produce amylase.2.Carrying out by mutagenic treatment protoplast induced mutation, ultraviolet mutagenesis, mutagen mutation, the activity of proteinases was strengthened by 198%. Then studied on bottle fermentation experiment of mutant strain 8, obtained the optimal fermentation condition: inoculation volume 5%, glucose is the most suitable carbonic source, (NH4)2SO4 is the most suitable nitrogen sources, the shaking speed is 210r/min, fermentation is performed at 37℃44h. Test effects of metal ions shows that Ca2+,Mg2+ enhanced protease activity, Ca2+ most significant, Zn2+ inhibition strain growth.3. Studied on ferment liquid by (NH4)2SO4 grading salt evolution, obtained crude diastase. Researches on proteinase of properties, proteinases vigor can reach the maximum when concentration of initial substrate casein is 0.1mol/L, pH is 7.0, the temperature is 50℃. And proteinases guaranteed stability at pH6-9, 40-60℃.4. In corn embryosperm, protein and starch firmly hang together. In order to release out starch , the binding force between protein and starch must be weaken or destroyed, so starch can be free starch in production process. Sulfurous acid could primely separate protein and starch, the most important question is the equipment corrosion, groundwater pollution, sulfurous acid residual in some degree. In this thesis, orthogonal test was conducted, statistic analysis of variance by DPS. The results showed that working time of proteinases and concentration of sulfurous acid was significant to the starch yield. Meanwhile make multiple comparison by SSR, compare all factors and combinations, to obtaine optimal combination: the concentration of sulfurous acid is 0.1%, the concentration of lactic acid is 0.6%, socked 18h, then peeled and removed embryo from corn kernel, regulated pH, added 20% fermentation liquid of protease, continue soak10h. The yield of starch is 67.71% and the soaking time is reduced 28hour by this method.In this thesis, the author had selected out stain in neutral condition, which can degradate corn protein, and had determined optimum reaction conditions, added ferment liquid to corn soak solution, reduced the content of SO2 .In this way, we can solve environmental pollution problems, and also improve quality of starch, promises a very high value in popularization and application.