Preparation, Characterization Of Calcium-binding Soybean Protein And Its Application To Pre-fried Microwavable Spring Rolls

With defatted soy protein in low temperature as main raw materials, 11S protein was separated from the total soluble protein and was modified. The thermodynamic and rheologital properties and structure of modified protein were studied. It could be applied to improve the crispness of microwave reheated pre-fried spring roll. We also studied the effect of calcium-binding protein added to the wrap of spring roll's on the rheology and retrogradation properties, retrogradation and stability during freeze-thaw. The mechanism of improvement crispness of the wrap by 11S calcium-binding protein was studied from the point of its change of physical chemistry properties.The separation conditions of 11S protein were ascertained first. By comparing some separation methods, we selected the method of Koshiyama and optimized the yield ratio. Denaturation temperature, calcium-binding capability and rheological characteristic of the modified protein were also studied. The method of infrared spectroscopy was used to analyze the apparent character peaks and secondary structure fitting character.The function of calcium-binding protein to improving the crispness of freezing pre-fried microwavable spring roll was studied. Different kinds of commercial spring roll stuffing's water activity were compared. The highest value as the benchmark, the mixture of sweetened bean paste and water was simulated and the stuffing was unified. We analyzed the effect of calcium-binding protein and its addition to the system of spring roll. The suitable addition of calcium-binding protein was 40~50 mg/g. Scanning Electronic Microscope (SEM) was used to observe the change of wrap's microstructure. In the condition of maintaining the crispness of the wrap, the best combinations of microwave heating power and time were as follows: the power 600 W, the reaction time 40 s and the addition of glycerin was 20 mg/g .Rapid Visco Analyser (RVA), Rheometer and Fourier Transform Infrared Spectroscopy (FTIR) were used to analyze the effect of calcium-binding protein to the wrap of spring roll's process of gelatinization. We found that according to the RVA, after calcium-binding protein was added, system's final viscosity was fallen down and the gelatinization temperature was improved. Rheometer was used to study the padana's static rheology and we found that with the increase of the shear rate, the panada added 11S protein fell its apparent viscosity. With the decrease of the shear rate, panada's apparent viscosity increase. The dynamic rheology of panada confirmed that the addition of calcium-binding protein could increase the storage modulus and decrease the loss modulus so as to improve the system's gelling ability. The system after gelatinization's result of FTIR indicated that the decreasing degree of protein's hydration was 1.596, the whole helix structure was fallen,β-extended strand structure improved significantly and the starch molecule's crystallization degree of starch was decreased by more than 10%. Finally we could confirm that with the addition of calcium-binding protein, moisture absorption property of modified protein in the mixing could be improved and released after gelatinization and improved the structure's well-ordered property so as to improve the crispness of spring roll.The effect of calcium-binding protein to the wrap of spring roll and panada's freezing character was studied. DSC was used to measure the effect of modified protein on the retrogradation of raw panada. We found that the addition of calcium-binding protein holden back retrogradation. The rate of retrogradation in 14 days was changed from 33.72% to 12.71%. The crystallization degree of the sample added the modified protein was changed from 52.1% to 17.5% measured by the method of X-ray diffraction. According to the change of the rate of water counting, we studied the effect of modified protein to the system's stability of freeze-thaw and found that 11S protein could improve the sample's stability efficiently.In conclusion, calcium-binding soy protein had the function of improving the crispness of freezing pre-fried microwavable spring roll, retarding the retrogradation efficiently and improving the stability in freeze-thaw. So it has nice value and future in the frozen instant flour product.