Screening And Improved Reaserch On Biological Modified Strains For Corn Flour

Corn is one of the three main food grains (wheat, rice, corn) and plays an important role in global food security. But because of its own composition, corn is not suitable for used to make the main food. How to improve the food and processing quality of corn flour and to make it suitable for the production of noodles, dumplings and other foods, is the corn research major scientific technology. This paper choose important microorganisms to modify the corn flour, hopes to improve the food and processing characteristics of corn flour,and make it suitable for used to make noodles, dumplings main food products, The main conclusions are as follows:1. We selected extracellular enzymes of microorganism, such as Bacillus subtilis B, Aspergillus oryzae, Aspergillus niger, Mucor pusillus, Rhizomucor and Mucor racemosus etc,to study the modification properties of biological enzyme of corn meal. The study investigated the solubility, water holding capacity,gel swelling, the physical properties, the pasting properties, corn powder X-ray diffraction (XRD) and microscopic observation of corn meal before and after modification. The results showed that corn dough modified by extracellular enzymes of Bacillus subtilisB was improved obviously in many aspects.So select the Bacillus subtilis B as the starting strain of corn flour modified.2. In this study, composition changes of corn flour were measured pre and post the modification of biological enzyme. After modified by enzyme, the fat, soluble solids, crude ash of corn meal were increased, with decreasing in true protein content of corn meal. the total amino acid content were increased by26.46%. The total starch and amylopectin starch content decreased significantly, meanwhile, amylose relative content increased.3. To modify the original strain B, we use four methods as follows:UV mutagenesis, nitrosoguanidine (NTG) mutagenesis,mutagenesis of diethyl sulfate (DES),microwave radiation mutagenesis. We obtained7strains of bacteria were genetic stability is good, and protease ability were obviously improved than start bacillus B (699.62U/ml). That is BU-18, BU-61, BN-32, BN-84, BD-5, BD-73and BM-74, their protease ability is1274.98U/ml,1102.56U/ml,1198.51U/ml,947.62U/ml,899.67U/ml,1201.11U/ml and1089.34U/ml respectively.4. We determine the optimum conditions of the Bacillus subtilis protoplast formation and fusion, the protoplast formation and regeneration rate is highest under following conditions: enzyme concentration of10mg/mL, bacteria age10h,hydrolysis temperature38℃, hydrolysis time was90min. The highest rate of Bacillus subtilis protoplast fusion happened under following conditions:temperature of35℃, PEG4000concentration35%, CaCl2concentration0.02mol/L, integration time10min. Through two rounds of genome shuffling, we get a genetic stability ideal mutant strain BSG1with protease activity2175.81U/ml,3.11times higher than the original strain,and the secretion of amylase secretion capacity than the original strain B did not change significantly.5. By comparison of the modification on corn flour by Bacillus subtilis between pre and post, the result shows that the improvement strain enhanced significantly in decomposition of true protein in corn meal, and have no obviously change when it act on starch. There are markedly improvements in the gel nature、pasting properties and TPA properties of corn flour, which are all better than com flour treated by original strain of extracellular enzymes. The springiness, gumminess,chewing and resilience increased by18.98%,52.6%,60.95%,25.89%respectively.6. The best culture condition for genetic transformation of Bacillus sutillus BSG1is as follows:2%soybean meal, corn flour1%,0.6%magnesium sulfate, medium pH7.0、bottle volume150/500ml、the initial inoculum5%、rotation speed280r/min and fermentation24hours at35℃. In this condition, bacillus subtilis BSG1secretion of protease enzyme reached2469.12U/ml, which1.13times compared with before optimization (2175.81U/ml). Not only increased production strains of protease, more optimized carbon and nitrogen sources, It will greatly reduce the production and com flour protease biological modified cost.7. Using corn dough chewing as the standard, the enzymatic reaction conditions of the modified cornmeal by biological enzyme was optimized, which is protease enzyme concentration800U/ml,20%of the com flour as a substrate, pH5.501, temperature51.720℃, reaction time18.790h. Under above condition, com dough chewing could get up to511.977g, which2.32times compared with com flour.It has the potential to make main food.