Mechanism Of Quality Change During Processing And Storage Of Preprocessed Noodles

Preprocessed noodles have shown a good development trend in the catering industry because of their green and healthy,convenient consumption.However,the regularity and mechanism of structural characteristics changes of starch and gluten proteins during the processing of preprocessed noodles are not clear.Therefore,in this dissertation,wheat flour was used to prepare preprocessed noodles.The physical and chemical properties,cooking characteristics and microstructure of preprocessed noodles were studied by simulating the precooking,cold storage and microwave reheating process.The changes and interactions between starch and gluten protein components during the processing of preprocessed noodles were analyzed,so as to clarify the mechanism during the processing and preservation of preprocessed noodles.On this basis,the quality improvement effect and mechanism of improvers on preprocessed noodles were explored.The main research results and conclusions are as follows:(1)Quality formation mechanism of preprocessed noodles during precooking stage.After pre-cooking preprocessed noodles at different times(0,30,60,90,120,150,and 180 s),the hardness and the content of bound water of preprocessed noodles gradually decreased,while the content of free water increased.The loss rate of sample after cooking for 180 s increased by 2.90%,and the water absorption increased by 43.61%.Cooking resulted in the decrease in the setback and breakdown viscosities for starch in preprocessed noodles and a crystalline structure translated from A type to V type.The analyzing of the secondary structure of proteins indicated that the formation of β-sheets structure,lead by precooking,reduced from 39.12%to 25.27%,β-turns structure increased from 32.43%to 44.81%,representing a gradual weakening of the preprocessed noodle gluten structure.During the precooking process,the starch granules were gelatinized and expanded,making full contact with the protein network structure,which sufficiently support the network structure.For preprocessed noodles with a short precooking time,it have no time for water to enter the central part of the noodles,resulting in a significant difference in taste between the surface and interior of the preprocessed noodles.The network structure collapses and breaks due to excessive precooking time,resulting in a softer texture and poor chewability of the preprocessed noodles.(2)The quality variation of preprocessed noodles during cold storage.It was found that the preprocessed noodles with 90 s showed the higher quality stability and sensory scores according to the studies on the total bacterial count,texture characteristics,quality stability,and sensory evaluation of preprocessed noodles with different precooking times and refrigerated(0-4 days).The breaking force and stretching distance of preprocessed noodles basically showed a downward trend with the extension of cold storage time,while microwave reheating could improve the breaking force and stretching distance of preprocessed noodles.Low-field nuclear magnetic analysis showed that the interaction between water molecules and starch/gluten proteins were weakened during the cold storage process,resulting in partial water precipitation.The crystalline type changed gradually from V-type to B-type,the relative crystallinity increased from 5.8%to 9.3%,and the short range order increased from 1.32 to 1.41.Microwave reheating can lead to a decrease in the relative crystallinity and short range order of starch.During the cold storage process,starch molecules re-form an ordered structure,the gluten network structure becomes loose,and microwave reheating reduces the relative crystallinity of starch and promotes the cross-linking of gluten proteins.(3)Quality improvement mechanism of preprocessed noodles.It was found that curdlan,xanthan gum,and soybean polysaccharides can affect the viscoelasticity of dough,as well as the hardness,breaking strength,and cooking loss of preprocessed noodles according to investigating the effect of modifiers on the rheological properties,texture properties,and the microstructure of dough.Taking into account,they have better improvement effects when the addition amounts are 0.3%,0.6%,and 1.5%,respectively.Curdlan and soybean polysaccharide can reduce the overall viscosity of preprocessed noodles,while xanthan gum can increase the viscosity of preprocessed noodles.The addition of 0.3%curdlan,0.6%xanthan gum,and 1.5%soybean polysaccharide decreased the crystallinity of preprocessed noodles from 10.1%to 8.74%,9.42%,and 9.18%,respectively.The enthalpy decreased from 1.01 J/g to 0.78 J/g,0.84 J/g,and 0.81 J/g,respectively.This indicating that the modifier can delay the regeneration of preprocessed noodles.Thermogravimetric and nuclear magnetic resonance analysis showed that curdlan,xanthan gum,and soybean polysaccharide can effectively delay the evaporation of water during the refrigeration process of preprocessed noodles,reduce the thermal weight loss of preprocessed noodles,and improve the water holding capacity of preprocessed noodles.The best performance is curdlan.In summary,the structure of starch molecules,the quality of gluten protein,and the interaction between them are the internal reasons affect the edible quality of preprocessed noodles during processing and storage.The study found that preprocessed noodles cooked for 90 s showed higher quality stability and sensory scores.The gluten network structure was enhanced by adding cordelan gum,xanthan gum and soybean polysaccharide.It was found that the edible quality of preprocessed noodles could be improved by adding 0.3%,0.6%and 1.5%,respectively,and the industrial production of preprocessed noodle can be further promoted.