| Soybean is one of the main economic crops in China, which has been extensively cultivated in north China. Concerning its characteristics of the edible oils and food protein resources, it is generally acknowledged that soybean becomes an indispensable source of food for human life. High protein, containing all essential amino acids, are part of advantages of soybean and it contains eight kinds of essential amino acids, the content of which is close to or higher than that of the United Nations food and agriculture organization (FAO)’s and the world health organization (WHO)’s ideal recommendations. Compared with animal protein, the nutritional value of soybean is able to meet the nutritional needs of human beings. And with the improvement of people’s living standard, modern diseases such as obesity, high blood pressure, the animal protein intake gradually reduce, plant protein intake increases gradually.With the rapid development of food industry, a lot of excellent functional properties of protein as raw materials for the food are needed. High protein, but complex structure, which leads to the limit of using scope and usage. Through chemical methods, many functions of the original nature of soy protein has been modified, such as solubility, water and emulsification, foaming, oily, have significant degree of improvement. The functional properties of soy protein has important application value in the food industry, meanwhile, it better meets the needs of the food industry. Soybean protein isolate is an important protein product, hydrolyzed by protease producing soybean peptides, peptides are much more absorbable than the protein and amino acid, at the same time, Soybean protein isolate have functions of reducing blood press, reducing blood fat and cholesterol, anti thrombosis, promoting the absorption of calcium, pHospHorus and trace elements, regulating immune function, antioxidant effect, low sensitivity to tranquilize mind, etc. Therefore the protease hydrolysis of soybean protein has been the hot topics in the study of people in recent years.Traditional research about the method of producing soybean peptides generated by protease hydrolysis of soybean protein is to determine the degree of hydrolysis product by trinitrobenzene sulfonic acid, formaldehyde titration determination of amino nitrogen, soluble nitrogen determination of trichloroacetic acid precipitation, to determine the optimal reaction conditions, such as temperature, acidity. Test method is complex and randomness. There is no precise quantitative research made to test the optimum experiment conditions for protease hydrolysis reaction. The purpose of this study is to overcome the shortcomings through microcalorimetry produced by the use of biochemical reactions. Directly measured by high sensitivity micro calorimeter trace amounts of heat in the process of enzyme catalytic reaction changes, which has the advantages of high sensitivity, simple operation.To increase the gel strength of soybean protein isolate, the semi-dry method was used to modify it by covalent modification with malt dextrin. Based on the results of single factor experiment, the Box-Behnken mode was applied to obtain the optimum conditions of modification. The Optimum reaction conditions were that the mass ratio of soy protein isolate and maltodextrin 4:1、the system water content 25%、reaction temperature 71℃, and the reaction time 30 min. Under the conditions, the gel strength of modified soybean protein isolate was 1982 g, which increased by 23.0% compared with that of unmodified one. The regression equation could also well predict the changes in the gel strength of the soy protein isolate with the changes in technological parameters of covalent modification. The results proved that semi-dry method can effectively increase the gel strength of soybean protein isolate.To increase the emulsifying properties of soybean protein isolate (SPI), the semi-dry method was used to prepare high emulsifying activity and emulsion stable soybean protein by cross-linking malt dextrin (MD). The central composite design based on the response surface methodology was applied to study the effects of MD content added, water content added, reaction temperature and time on the emulsifying properties of SPI, and the regression models were established between the emulsifying properties and different factors. The results showed that the emulsifying activity of SPI was 71.9 mL/g, and its emulsion stability was 91.2% under the conditions of 39% MD added,18% water content at 65℃ for 8.4 h.Based on soybean protein isolate as the research object, using the trace calorimetry as the research method, measured by micro calorimeter protease to soy protein catalytic reaction of thermal power-time curve, according to the thermal dynamic theory and comparative schedule method to resolve the different temperature, acidity and metal ions exist michalis faloutsos of enzyme catalytic reaction constant (Km, K’) and the maximum rate (Vmax), establish m kelly’s constant with temperature, pH, and metal ions, the relation between enzymatic reaction to obtain the optimum temperature, pH and metal ions on the influence of enzyme catalytic reaction activation or inhibit effect.Studies have shown that the optimum temperature(319.19K) for neutral protease to soy protein catalytic reaction, the optimum pH (7.13). Metal ions (Li+, Na+) belongs to the type of competitive inhibition.The rule of Inhibition is:in the same concentration of Li+> Na+; In different concentrations, with the increase of metal ion concentration,the inhibition increased. Metal ions (Cd2+, Mn2+) is belong to the type of competitive activation. The rule of activate is:in the same concentration of Cd2+>Mn2+. In different concentrations, with metal ion concentration increasing, the activation increased.Studies have suggested that optimum temperature (323.27K)for soy protein with trypsin catalytic reaction, the optimum pH (7.77). Metal ions (Ca2+, Mg2+) belongs to the type of competitive inhibition. The rule of Inhibition is:in the same concentration of Ca2+>Mg2+ In different concentrations, with the increase of metal ion concentration,the inhibition increased. Metal ion (Na+, K+) is belong to the type of competitive activation. The rule of activate is:in the same concentration Na+>K-; In different concentrations, with the metal ion concentration increasing, activation increased.Under the condition of optimum temperature, the optimum pH, to measure pineapple protease catalytic soy protein reaction of thermal power-time curve when the metal ions reversible competitive, by comparing the quantitative,metal ions (Li+, Na+) belongs to the type of competitive inhibition. The rule of Inhibition is:in the same concentration of Li+> Na+; In different concentrations, with the increase of metal ion concentration,the inhibition increased; Metal ion (Ca2+, Mg2+) belong to the type of competitive activation. The rule of activate is:in the same concentration Ca2+>Mg2+; In different concentrations, with the increase of metal ion concentration,the activation increased.Studies have shown that the optimum temperature (329.5 K)for alkaline protease to soy protein catalytic reaction, the optimum pH (8.25). Metal ions (Pb2+, Ag+) belongs to the type of competitive inhibition. The rule of inhibition is:in the same concentration of Pb2+> Ag+ In different concentrations, with the increase of metal ion concentration,the inhibition increased. Metal ions (Na+, Mg2+) is belong to the type of competitive activation. The rule of activate is:in the same concentration of Na+>Mg2+; In different concentrations, with the increase of metal ion concentration,the activation increased.Measuring thermal power-time curve of the soybean peptides to the metabolism of e. coli, we get the effects of soybean peptides on metabolism of e. coli. Research shows that when the concentration of soybean peptides C< 2.06 mg/ml, soybean peptides can promote the growth metabolism of e. coli in order to role; When C> 2.06 mg/ml, bacteriostatic effect.Measuring thermal power-time curve of the soybean peptides to salmonella metabolism, we get the effects of soybean peptides on salmonella metabolism. Research shows that when the concentration of the soybean polypeptide C< 2.67 mg/ml, soybean peptide’s influence on the growth of salmonella metabolism is in promote role; In C> 2.67 mg/ml, bacteriostatic effect.Measuring thermal power-time curve of soybean peptides to yeast metabolism, we get the effect on soy peptide to yeast metabolism. In the experimental concentration range. In different concentrations of soybean peptides,the growth rate of yeast is greater than that of yeast without soybean peptides. On the effect of it, soybean peptide is a promoting role to the growth of yeast metabolism.The innovation of this article is for the first time using the method of trace calorimeter to measure protease to soy protein catalytic reaction of thermal power-time curve, calculating michalis faloutsos constant and the maximum rate in enzyme catalytic reaction, to get optimum temperature and the optimum pH of enzyme catalytic reaction by quantitative. First measure of metal ions to the influence of protease hydrolysis of soybean separation protein catalytic reaction heat power-time curve, obtained the effect of enzymatic reaction of metal ions to activate or inhibit. First measure of thermal power-time curve of soybean peptides on escherichia coli, yeast, the yeast metabolism, calculated the growth of bacteria metabolic rate constant, got effect of the soy peptide on promoting bacteria and bacteriostatic. In this paper, the study of protease catalytic hydrolysis reaction to provide quantitative research methods can be found. For the domestic and foreign scholars study,the reaction conditions of protease hydrolysis of soybean protein can be used and the paper provides theoretical basis. Besides, the reaction mechanism for the development of the pHysiological functions of soybean peptides can be provided deep theoretical support. |
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