Study On The Factors Of Processing And Quality Of Dried Kongxin Noodles And The Underlying Mechanism

Noodles,which have a history of more than 4,000 years,are one of the most important traditional staples in Asian countries.In recent decades,although the yield of noodles increased sharply,the development of high-quality noodles remained low.Chinese traditional dried Kongxin noodles(CTKNs)are the most famous traditional high-quality noodles,which are liked by consumers because of their short cooking time and nice mouthfeel.However,the development of CTKNs is inhibited by its complex process technology and high salt content.As a result,the production of CTKNs remains in villages and small-scale industries.Deep research on the processing and quality of CTKNs was therefore conducted,and a processing technique of machine-made dried Kongxin noodles(MDKNs)with a low salt concentration was developed.First,the quality and physiochemical properties of the major components of CTKNs were investigated by comparison with machine-made dried noodles(MDNs).It was discovered that the cooking quality and texture characteristics of CTKNs were much better than those of MDNs.The optimal cooking time and cooking loss of MDNs ranged from 480 s to 540 s and from 7.64%to 8.85%,respectively.The optimal cooking time and cooking loss for CTKNs was significantly(P<0.05)less,at 255 s and 6.14%,respectively.The elasticity,firmness,and chewiness of CTKNs were significantly(P<0.05)higher than those of MDNs.The microbial metabolism during CTKNs processing was much more active,resulting in higher crystallinity,swelling power,and gelatinization enthalpy and lower viscosity of starch.The changes in starch thermal properties were responsible for the shorter cooking time,lower cooking loss,and higher elasticity.Additionally,the pores and continuous gluten network of CTKNs formed during processing also accounted for the higher cooking quality and texture characteristics of CTKNs.Next,the effects of the NaCl addition and resting on the rheology property of dough and the underlying mechanism were investigated.The small dynamic rheology and the extensional property increased when the addition of NaCl increased from 0 to 5%.These increases were due to the fact that NaCl increased the Glutenin macropolymer(GMP)content in dough by increasing the hydrogen bonds and hydrophobic interactions among the gluten subunits.When more than 5%NaCl was added,the gluten in the dough aggregated excessively,resulting in decreased dynamic rheology and extension.The resting process resulted in decreased G?,G??,and extensional strength,while it increased the values of Tan?,extensibility,and the extensional area.These phenomena were caused by gluten relaxation and gliadin reaggregation.Additionally,the effect of NaCl on the quality of CTKNs and the underlying mechanism were also investigated.When the addition of NaCl increased from 3%to 5%,the cooking loss of CTKNs increased from 6.14%to 7.20%,and the elasticity decreased from 21.22 to 16.98g·s^-1.The increased addition of NaCl inhibited the metabolism of microorganisms,leading to decreased starch swelling power.This effect could explain the decreased elasticity of CTKNs.The increased salt addition also resulted in decreased cross-linking of gluten,which also contributed to the increased cooking loss and decreased elasticity of CTKNs.Furthermore,the effects of yeast addition,multistep fermentation,water addition,and salt on the quality of MDKNs were investigated.When the amount of yeast was increased from 0to 0.75%,the optimal cooking time and cooking loss of MDKNs decreased from 720 s to 555s and from 8.04%to 6.64%,respectively,while the cooking loss increased to 7.09%as the amount of yeast was further increased to 1.00%.The elasticity and chewiness of MDKNs increased significantly(P<0.05)by adding yeast ranging from 0 to 1.00%,and the firmness increased significantly(P<0.05)when the level of yeast was 0.25%.The two-step fermentation(a)was more effective in the production of MDKNs compared with other fermentation methods,as it not only made the pores more clear and shortened the optimal cooking time but also had no negative effect on the appearance of MDKNs.The texture characteristics of MDKNs decreased significantly(P<0.05)when the amount of water added exceeded 35%.The addition of NaCl decreased the optimal cooking time and increased the elasticity of MDKNs significantly(P<0.05),while it significantly(P<0.05)increased the cooking loss.The addition of NaHCO₃ shorted the optimal cooking time and increased the firmness and chewiness of MDKNs significantly(p<0.05).At last,the quality of MDKNs was improved by adding NaHCO₃,and the underlying mechanism was also studied.When the addition of NaHCO₃ increased from 0 to 0.3%,the optimal cooking time and cooking loss of MDKNs decreased from 405 s to 360 s and from6.06%to 5.52%,respectively.Additionally,the texture characteristics of MDKNs also increased significantly(P<0.05)when the level of NaHCO₃increased from 0 to 0.3%.These increases in cooking quality and texture characteristics of MDKNs were due to the promoted starch gelatinization and gluten cross-linking by NaHCO₃.When the addition of NaHCO₃reached 0.4%,the cooking loss of MDKNs significantly(P<0.05)increased to 6.42%and the firmness and chewiness significantly(P<0.05)decreased to 355 g and 1515 g·s,respectively.The decreased cooking quality and texture characteristics were related to the excessive cross-linking of protein induced by 0.4%NaHCO₃.The effect of starch on the quality of MDKNs was investigated indirectly using MDNs prepared with different amounts of?-amylase.Adding?-amylase markedly increased the relative crystallinity and swelling power of starch,while decreased the pasting viscosity and retrogradation properties.These changes led to decreased optimal cooking time and increased elasticity.The changes in starch thermal properties also inhibited the cross-linking of protein,which resulted in increased cooking loss and decreased firmness and chewiness.It can be concluded that the starch hydrolyzation can improve the elasticity of noodles,while it can also lead to decreased firmness and chewiness.