The Improvement And Mechanisms Of Noodle Quality By High Water Addition And Fractional Water Addition Under Vacuum Mixing

Mixing is a key process in noodle processing,and it is the basis for the formation of food product structures in the future.It is known that high addition and fractional addition of water in vacuum mixing can promote the hydration of each component in flour and adjust the water distribution among the characteristic components,thereby improving the rheological properties and surface viscosity of the dough,and eventually improving the eating quality of the final products.However,the methodology for evaluating the effect of mixing and its improvement mechanisms have not yet formed a systematic theory.Based on this,in the present studies,the high water-added and the fractional water process under vacuum mixing were optimized based on the color difference method and the particle size of the flour floc,respectively;The effect mechanisms of the kneading process parameters on the noodle quality were explored from the perspectives of water distribution,protein secondary structure changes and gluten network microstructure.Finally,the actual improvement effect of high wateradded vacuum mixing and adding water in stages were further verified through the pilot test.The main contents and results of the paper are as follows:(1)Caramel pigment was used as color developer,and the mixing time and vacuum degree of the high water-added dried noodles were optimized based on the change rule of the color of dough sheets,and the optimization method was verified by the chewiness of the cooked noodles.In order to preliminarily clarify the improvement and mechanism of high water-added and vacuum-mixing effect on the noodle quality,the edible quality of high water-added and low water-added noodles under normal pressure and optimal vacuum degree were compared,respectively,and by the changes of gluten network structure were quantitatively analyzed.The results showed that it was feasible to optimize the kneading process parameters by using the color difference method.The optimum mixing time for high water-added noodles was 9 min,and the optimal vacuum degree was-0.06 MPa.Compared with the normal pressure dough-mixing,the chewiness and smoothness of dried noodles were improved under this condition,among which the chewiness was significantly increased by 19.6%.Furthermore,the chewiness and smoothness of the noodles were much better than those of vacuum low water-added dried noodles,respectively.The chewiness was 1.25 times that of the low water noodles,and the smoothness was also the best.It was found that the average length and width of the gluten network under the optimal mixing conditions were the smallest through the quantitative analysis of the gluten network of dough sheets,and the branching rate was significantly expanded by 26.9% compared with the low water-added dough sheets,reaching at the maximal value.It was speculated that the color difference method could be used to optimize the dough-kneading process parameters.Under the optimized kneading conditions,the water distribution of the dough sheets was the most uniform,and the gluten network structure was denser and uniform,so that the edible quality of38% high water-added noodles reached the best parameters.(2)Taking the tensile properties of the dough sheets and the particle size distribution of the flour floc as the evaluation indicators,the water addition ratio and the dough mixing time were optimized under the two-times water addition methods,respectively.The accuracy of the optimization results and the reliability of using the particle size distribution of floc dough as the evaluation index were verified by comparing the comprehensive quality of fresh noodles.And the mechanism of graded water addition on the quality improvement of fresh noodles was preliminarily clarified by analyzing the changes of water distribution and gluten network structure under different water addition methods.The results showed that the optimal water addition time was 3+6 min and the water addition ratio was 2:1.Under this process,the floc content of large particles(d>4 mm)formed was the smallest,and the floc content of medium and small particles(0.25 <d<4 mm)was the largest.And the color of fresh noodles was the whitest,the cooking loss was significantly reduced,and the chewiness,hardness,and smoothness of noodles were significantly improved by about 16% to 21%compared with one-time addition of water.Compared with once-addition of water,the bound water content in the dough sheets of two times-addition of water increased by17%,and the content of α-helix and β-sheet in the protein significantly increased;the average length and width of the protein in the gluten network significantly decreased,and the branching rate markedly increased.It could be observed that adding water twice(mixing time 3+6 min,adding water ratio 2:1)enhanced the water holding capacity of the dough sheets and promoted the formation of a more compact,uniform,and orderly gluten network structure,thereby significantly improving the comprehensive quality of fresh noodles.(3)Under the actual industrial production conditions,different amounts of water were used to make dried noodles,and different methods of adding water were used to make fresh noodles,and the comprehensive quality of dried and fresh noodles was compared to verify the quality of the noodles with high water vacuum mixing and graded water respectively..Then the mechanism of high water and vacuum mixing on the quality improvement of noodles was further explored through the change of protein characteristics.The results showed that under industrial conditions,the tensile displacement of the dough sheet made by 39% high water addition and vacuum kneading significantly increased compared with the low water addition,and the ductility perpendicular to the calendering direction was significantly improved by about21%.The bending resistance of the highwater-added dried noodles was significantly enhanced,the cooking loss was reduced,and the edible quality such as the chewiness and smoothness were significantly improved.Under the condition of high-water addition,the content of SDS-extractable protein and free sulfhydryl groups in dried noodles significantly decreased,the content of hydrogen bonds and β-sheets markedly increased,and the content of β-turns significantly decreased.At the same time,the brightness of the fresh noodles was also significantly improved,the cooking loss of the noodles was reduced,and the chewiness and smoothness of the fresh noodles were significantly enhanced by adding water in stages.Especially when the adding water ratio is 2:1,under the process of kneading the noodles for 3+9 minutes,the texture of the fresh noodles was significantly enhanced by about 8.2%,and the smoothness was improved by about 15%.In conclusion,the high water-added and vacuum kneading significantly improved the comprehensive quality of dried noodles under industrialized conditions by improving the cross-linking degree and stability of gluten protein.And the addition of water in stages also significantly improved the overall quality of fresh noodles.