Effect Of Wheat Starch Granule Size On The Quality Of Dried Noodles And The Underlying Mechanism

Starch,the main compon ent of wheat flour,exists in the form of large and small starch granules,namely A-type starch granule（AS）and B-type starch granule（BS）.The function of starch is particularly prominent in the heating process,which has an important contribution to the quality of cooked products.In recent years,the research on the influence of flour components on noodle quality mainly focuses on protein characteristics,while the contributions of starch to the rheological properties of noodle dough and the quality of dried noodles have not been thoroughly studied.Dried noodles,a traditional staple food in China,are noodles with the largest production,the widest range of sales and the largest production value in China.At present,the eating quality of noodles is mainly improved by adding improvers,but the green safety is poor.The green safety improvement technology and its mechanism of controlling the quality of dried noodles based on the starch granule size need to be further explored.In view of this,this research focused on the effects of the granule size of wheat starch on the dough sheet properties and noodle quality with or without saline-alkali condition,and the effect mechanism of starch granule size distribution on the rehydration behavior and cooking quality of noodles was also explored from the perspective of interaction between starch and protein during cooking,thus revealing the mechanism of starch granule size affecting noodle quality.（1）The effects of starch granule size on the viscoelastic property of noodle dough sheets and the underlying mechanism were investigated.Dough with a high ratio of B-type starch granules showed higher viscoelastic modulus（G′′and G′）,initial force（F₀）,percent stress relaxation（SR%）,and smaller maximum creep compliance(J_max),indicating higher viscoelasticity and strength.This was mainly attributed to the higher water-binding capacity and filling ability of B-type starch,which promoted the non-covalent bonding between starch and protein in dough.Compared with large A-type starch granules,small and irregular B-type starch granules were more likely to fill the gaps in the dough matrix and promoted the formation of uniform and dense structure,thus enhancing the strength of the dough.（2）The mechanical properties,microstructure,cooking quality,and textural characteristics of noodles with different B/A-type granule ratios were investigated.The relationship between starch granule size and the quality of noodles was discussed from the differences in structural and physicochemical characteristics of A-and B-type granules.A-type granules showed higher molecular weight,relative crystallinity,and short-range order,while B-type granules had more short amylopectin branch chains.The higher swelling power and pasting viscosity of A-type granules caused a decrease in the hardness and elasticity of the cooked noodles,while the lower pasting viscosity and higher gel strength of B-type granules led to a significant increase in the hardness,chewiness,and elasticity of the cooked noodles,which contributed to the improvement of noodles quality with a high ratio of B/A-type granules.With the increase of B/A-type granule ratios,raw noodles showed a denser structure,higher bending strength and flexibility,and the hardness（increased by 26.4%）,chewiness（increased by 20.0%）,and resilience（increased by 17.0%）of cooked noodles were significantly increased（P<0.05）.The mechanical properties of raw noodles and the textural characteristics of cooked noodles were significantly negatively correlated with the z value of frequency sweep and the maximum creep compliance(J_max)（r=-0.998～-0.883,P<0.05）,and significantly positively correlated with the k value of frequency sweep and the percentage of stress relaxation（SR%）（r=0.889～0.986,P<0.05）.（3）The effects of salt and kansui on the viscoelastic property of noodles with different starch granule sizes and the underlying mechanism were investigated by comparison.The addition of salt slightly reduced the viscoelasticity of the dough sheet,while the effects of kansui were the opposite,and both showed more obvious effects on the dough sheets with a low ratio of B/A-type granules.Under the same amount of salt or kansui,the viscoelasticity of the dough showed an increasing trend with increasing of the ratio of B/A-type granules.Salt promoted the non-covalent bond interaction between protein molecules,while kansui significantly enhanced the covalent cross-linking of gluten proteins,thus improving the viscoelasticity of dough.B-type starch inhibited the aggregation of protein caused by salt or alkali,whereas which was beneficial to enhance the non-covalent bond in the dough,leading to the increase of the viscoelasticity of dough sheets with a high ratio of B/A-type granules.（4）The effects of salt and alkali on the quality of noodles with different starch granule sizes and the underlying mechanism were also investigated.During noodles cooking,salt caused the gluten polymerization to decrease,and a low concentration of kansui（0.5%）promoted the formation of the intermolecular disulfide bond,while high concentration of kansui（2%）induced a strongerβ-elimination reaction and led to a decrease of gluten polymerization.Salt promoted absorption and gelatinization during cooking,thus shortening the cooking time and improving the elasticity.Kansui improved the swelling and gelatinization of starch granules and the cross-linking of protein,which significantly improved the hardness,resilience,and tensile properties of cooked noodles with a low ratio of B-/A-type starch.However,a high concentration of kansui led to higher cooking loss（increased by 44.9～66.1%）,lower water absorption（decreased by 2.9～13.6%）,and lower elongation（decreased by13.8～16.15%less）of noodles with high ratio of B/A-type granules.（5）The impact of starch granule size on the rehydration behavior and changes of components and microstructure during noodles cooking and the underlying mechanism was also studied.During the cooking process,the water penetrated gradually from the surface to the core,the absorption increased sharply first and then slowly,and the large A-type starch granules promoted the water uptake of noodles,as well as the protein appeared to react at a slightly earlier time than starch.Noodles with a high ratio of A-or B-type starch exhibited a more rapid water migration and faster structural changes at the initial stage and then became slower later,whereas noodles with the 50:50 ratio of A-/B-type starch showed high water-binding capacity and absorption,as well as good coordination between starch gelatinization rate and protein aggregation rate,contributing to the noodle moderate firmness and resilience.Good coordination in structural transformations of starch and protein was needed to achieve good quality of cooked noodles.The findings of the research suggested that starch granule size had a significant effect on the dough viscoelasticity and noodle quality.The suitable ratio of B/A starch granules could promote the starch-protein interaction,enhance the integrity and compactness of gluten network structure,which can improve the strength of noodle dough and the processing performance and quality characteristics of noodles.The variation of starch granule size had the potential to improve the structural features and textural characteristics and provide theoretical basis for the green safety improvement technology based on starch granule sizes to control the quality of noodles.