| Wheat gluten is the by-product of the production of wheat starch. Because wheat gluten is rich with hydrophobic amino acids, intramolecular disulfide bonds and intermolecular disulfide bonds, it shows poor solubility, poor dispersion, and it is difficult to meet he requirement of food processing. The texturization process with extruder could significantly improve the texture, taste and nutritional value of wheat gluten and make wheat gluten well digested by human. Therefore, process parameters of extrusion texturization and the physiochemistry, texture property, chemical bonding and functional properties of the wheat gluten were studied, and the results were as follows:(1) Single factor experiment was used to research the influence of the process parameters of extrusion texturization (water addition, extrusion temperature, screw speed and feed speed) on the appearance, physiochemical indexes (nitrogen solubility index), expansion ratio and rehydration ratio), texture properties (springness, hardness, adhesiveness, and chewiness), and texturization degree of the wheat gluten. The determined process parameters of extrusion texturization were as follows:water addition 40%-45%, extrusion temperature 150-170℃, screw speed 240-300 r/min and feed speed 19-23 kg/h. Based on the single factor experiment, response surface method (RSM) and Multiple Regression Analysis Method were employed to optimize and verified the process parameters of extrusion texturization. The results showed that optimal process parameters were as follows:water addition 44%, extrusion temperature 160℃, screw speed 280 r/min and feed speed 21 kg/h. Under these conditions, the expansion ratio of the wheat gluten was 126.46%, the rehydration ratio was 249.49%, the coefficient of springness was 0.549, the coefficient of hardness was 9988.08 g, the coefficient of adhesiveness was-60.498 gsec, the coefficient of chewiness was 2650.42, the coefficient of resilience was 0.112, the expansion ratio was 126.46%, and the texturization degree was 2.33.(2) The influence of L-cysteine, monoglyceride, sodium alginate and sodium tripolyphosphate on the extrusion texturization of wheat gluten was studied. The results showed that with the addition of L-cysteine and monoglyceride increasing, the appearance of wheat gluten became uneven and the degree of expansion and texturization reduced gradually. When the addition of L-cysteine and monoglycerides were greater than 0.09% and 0.6%, respectively, the extrusion products had not formed the texturization structure. Owing to the addition of sodium alginate, the extrusion products were puffed fully and filled with uniform pores. Adding different quantity of sodium alginate, the expansion ratio and rehydration rate of products were larger than 120% and 180%, respectively. Besides, the addition of sodium tripolyphosphate could improve the generation of texturization structure of wheat gluten and the surface of the extrusion products were light-colored and smooth with uniform pores. Once the amount of sodium tripolyphosphate was 0.3%, the expansion ratio of the products was the highest (129.18%) and rehydration rate was more than 50% higher than that of products without sodium tripolyphosphate.(3) With the optimal additives (monoglyceride, sodium alginate and sodium tripolyphosphate) and the optimal process parameters of extrusion texturization (water addition, extrusion temperature, screw speed and feed speed) above, the fourier transform infrared spectroscopy (FT-IR) showed that the content of unstable α-helix of the products was decreased to 0%, and the content of β-sheet, β-turn and random coil of the products were all increased. It was indicated that in whole or in part of unstable α-helix were transformed to relatively stable β-sheet, β-turn and random coil. After added L-cysteine, the contents of α-helix, P-turn and random coil of texturized proteins were increased by 3.37%,2.94%, and 1.26%, respectively, and the content of P-sheet was decreased by 7.58%. Under the all above conditions, the correspondent wavelengths of respective peaks of secondary structure of obtained products hardly drifted in a range of 1600-1700 cm-1 wavelengths, which indicated that there was no generation of secondary structure.(4) The changes of the physicochemical characteristics and functional properties of wheat gluten and texturized wheat gluten were also studied, and the results were as followed:after extrusion, the water holding capacity and the digestibility of texturized wheat gluten were increased by 70.21% and 11.88%, respectively, and the NSI and the content of free sulfhydryl were decreased by 37.71% and 36.10%, respectively. The protein solubility analysis showed that the order of the maintenance of intermolecular forces of wheat gluten and texturized wheat gluten before and after extrusion were as follows:disulfide bonds and non-covalent bonds, non-covalent bonds, native state and disulfide bonds. The amino acids analysis showed that cysteine was decreased 15.70% which was the maximum loss amount in the extrusion process. According to the changes of thermodynamic properties, the thermal enthalpy (AH) of texturized wheat gluten was increased by 147.63%, which indicated that new chemical bonds with higher bond energy were formed in the texturized wheat gluten. There was no new absorption peak in FT-IR spectrum, indicating that no new peptide bond existed in the texturized wheat gluten. The result of protein gel electrophoresis indicated that the breaking, polymerization, recombination and cross-linking of chemical bonds between the proteins were generated during the process of extrusion. The images of scanning electron microscope (SEM) showed that the texturized wheat gluten had an orderly fiber structure. |
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