Improvement Of Nutritional Quality And Fibrinolytic Enzyme Activity Of Soybean Meal By Fermentation With Bacillus Subtilis XZI125

Soybean meal (SBM) features the following merits as an abundant source, a high protein content and a complete and balanced nutrition, being rich in minerals, vitamins and essential amino acids. Among them, soybean peptides are the hydrolysates of soybean protein, which have the same amino acid composition as soybean protein. Besides, they exhibit more excellent physiological and functional properties and processing characteristics than those of soybean protein, which can be widely used in food and medicine industries. The microbial fermentation of SBM is a promising method for increasing the content of soybean peptides from the protein hydrolysis via protease produced by microorganisms. Furthermore, many complex enzymes and other active substances may be produced by microorganisms in the fermentation process. In addition, the main anti-nutrition factors which affect digestion and absorption are reduced in fermented SBM culture effectively, the nutritional quality and availability rate are also improved.In recent years, our team obtained a high fibrinolytic enzyme producing strain named as B. subtilis XZI125. In this work, the objectives were:(1) to study the optimum laboratory conditions of liquid and solid-state fermentation in order to obtain high yield of fibrinolytic enzyme and soybean peptides;(2) to investigate the fibrinolytic enzyme characteristics of the freeze dried product of fermented SBM under the optimized solid-state condition. The main results are described as follows:1. Screening of the key factors that influence fibrinolytic enzyme activity and soybean peptides yield in the Bacillus subtilis XZI125liqid-state fermentation. The single factor experiment and Plackett-Burman design were undertaken to screen the key factors rapidly from these related factors affecting the fibrinolytic enzyme activity and the soybean peptides yield in the liqid-state fermentation. By analyzing the statistical regression and the prediction profiler, the medium volume, soybean meal content and inoculation volume were found to be the most important factors for the fibrinolytic enzyme activity, while glucose, inoculation volume, soybean meal content, pH, seed age and fermentation time were the significant factors for the yield of soybean meal.2. The Optimization of fermentation conditions for Bacillus subtilis XZI125liqid-state fermentation producing fibrinolytic enzyme and soybean peptides was studied. On the basis of the previous results, the steepest ascent design and response surface method of Box-Behnken design were applied to optimize the production of the fibrinolytic enzyme and soybean peptides, respectively. The results show that the optimum values of the medium volume, soybean meal content and inoculation volume for obtained the most fibrinolytic enzyme activity were50mL/250mL,7.22%and4.24%, respectively. While the optimum values of glucose, soybean meal content and inoculation volume for the most production of soybean peptides were11.09%,11.44%and2%, respectively. The optimized cultivation conditions allowed the fibrinolytic enzyme activity and soybean peptides yield to be increased to2146.71IU/mL and9.24mg/mL, respectively.3. The effect of soybean meal solid-state fermentation by Bacillus subtilis XZI125and the characteristics of fibrinolytic enzyme were studied. The optimum solid-state fermentation conditions were obtained by single factor and orthogonal experiment as follows:fermentation temperature30℃, incubation time48h, grinding particle size of SBM40mesh, pH7.0, material loading10g, glucose1.5%, water content and inoculum size were1.0mL/g and3%, respectively. Under the optimized condition, fibrinolytic enzyme activity and the soybean peptides yield reach1347.35IU/g and171.32mg/g respectively. Additionally, the contents of TI, phytic acid, urease and antigenic proteins were in varying states of degradation in fermented SBM compared to SBM. Characteristics of the fibrinolytic enzyme of the freeze dried SBM from solid-state fermentation were evaluated. The results revealed that optimum temperature and pH of fibrinolytic enzyme was37℃and7.0, respectively. The enzyme appeared to be stable in the range of25～37℃and pH7.0-9.0, respectively. The enzyme activity was enhanced in the presence of Fe2+, Mn2+. Metal ions such as Mg2and Ca2+showed partially inhibition on the activity of the enzyme. The higher concentration of the metal ions or chemicals was, the stronger inhibition showed.Glycerin,gelatin and amylomaltose could effectively reduce the thermal denaturation of fibrinolytic enzyme and enhance its thermal stability.