Effects Of Konjac Glucomannan On Dough Characteristics And Aggregation Behavior Of Wheat Gluten With Different Strengths

Konjac glucomannan(KGM)is used as a food additive to improve the properties of dough and the quality of pasta products.In addition,as a soluble dietary fiber,KGM can increase the body’s satiety,reduce the absorption of calories and nutrients,lower cholesterol and have a preventive effect on obesity.However,the addition of KGM will result in changes to the physicochemical properties and eating quality of the pasta products,which will limit the application of KGM in pasta products.In this study,the effects of KGM on the characteristics and gluten aggregation behaviour of wheat doughs with three different gluten contents:weak,middle and strong gluten,the textural and tensile properties of doughs and gluten aggregation,the composition,interaction and structural changes of gluten proteins were investigated,and the material basis of KGM regulation of gluten protein aggregation behaviour of wheat with different gluten contents was elucidated.The main findings of the study are as follows:The results of the effect of KGM on the properties of wheat dough showed that the hardness of the three types of al dente wheat dough reached a maximum of 1510.36 g,2185.26 g and 2813.95 g at a KGM substitution rate of 2%for weak,middle and strong al dente wheat doughs respectively;With increasing KGM substitution,the adhesion and elongation of wheat doughs of weak,middle and strong tenacity gradually increased,while the area of the stretching curve,the stretching resistance and the stretching ratio of the dough gradually decreased,with the area of the stretching curve decreasing to 54 cm2,68 cm2 and 120 cm2 and the stretching resistance decreasing to 206 BU,218 BU and 271 BU;The tensile ratios were reduced to 1.4,1.3 and 1.3;the PMT of the three gluten wheat flours gradually shortened with increasing KGM substitution,and the MT and AgE of the three gluten wheat flours gradually increased at 2%and 5%KGM substitution,but decreased with the addition of 10%KGM.The effect of KGM on the composition of wheat gluten proteins showed that the molecular weight distribution of gluten protein subunits was slightly reduced at 15-25 kDa under 10%KGM treatment,but there was no significant change in the molecular weight distribution of wheat gluten protein subunits of weak,middle and strong gluten strength;The results of exclusion chromatography(SE-HPLC)further demonstrate that KGM does not cause changes in the glutenin subunits;At KGM substitution rates of 2%and 5%,the content of α-and γ-gliadin in weak gluten wheat gluten proteins decreased by 1.5%and 8%,respectively,and when KGM substitution rates increased to 10%,the content of α-and γgliadin proteins increased again to 46.27%.Whereas for middle gluten wheat gluten proteins,the content of HMS subunits decreased significantly from 15.72%to 13.59%with increasing KGM substitution rate;In strong gluten wheat gluten proteins,the content of D-LMS,HMS and B/C-LMS gradually decreases.As the KGM substitution rate increases,the content of wheat gluten protein macromers gradually decreases in all three different gluten wheats:weak,middle and strong,which will be detrimental to the aggregation of gluten proteins.The results of the effect of KGM on the interaction force of wheat gluten proteins showed that the stronger the gluten of wheat flour without the addition of KGM,the less free sulfhydryl groups and the higher the content of disulfide bonds in gluten proteins;A significant increase in free sulfhydryl groups and a decrease in disulfide bonds in the three gluten proteins of weak,middle and strong gluten compared to the control when the KGM substitution rate was higher than 5%;In addition,ionic bonding,hydrogen bonding and hydrophobic interactions in the three types of gluten proteins of weak,middle and strong gluten were slightly enhanced with increasing KGM substitution rates;When KGM was not added,the absolute values of zeta potential on the surfaces of weak,middle and strong gluten wheat gluten proteins were 7.29 mV,7.23 mV and 6.86 mV,respectively.When the substitution rate of KGM was greater than 5%,the negative charges on the surfaces of weak,middle and strong gluten wheat gluten proteins were significantly increased,which increased the electrostatic repulsion on the gluten protein surfaces,indicating that KGM was an important factor in inhibiting the aggregation of gluten protein molecules important reason.As the KGM substitution rate increased,the disulfide bond content in the GMP of weak,middle and strong gluten wheat gradually decreased,indicating that KGM can inhibit gluten protein aggregation by breaking the disulfide bonds in the GMP.Effect of KGM on wheat gluten structure and GMP particle size distribution:KGM reduces the α-helix structure and increases the β-sheets structure in weak gluten wheat gluten proteins,promoting the stability of the gluten structure.However,KGM caused some of theα-helix structures in the gluten proteins of middle gluten wheat to deconvolve into random coil structures,destroying the orderliness of the gluten structure.The 10%KGM resulted in a reduction of β-turn to 12.84%and an increase of α-helix and random coil structure to 23.65%and 16.69%respectively in strong gluten wheat gluten protein,destabilizing the gluten structure.Compared to the control,10%KGM enhanced the continuity of the reticulation of the weak gluten wheat gluten,but severely disrupted the reticulation of the middle and strong gluten wheat gluten.At higher KGM substitution rates(10%),small and medium size GMP particles of weak gluten wheat aggregated and formed more medium and large size GMP particles;in contrast to weak gluten wheat,medium and large size GMP particles;In contrast to weak gluten wheat,the medium and large GMP particles of middle and strong gluten wheat undergo depolymerization,forming more smalls GMP particles.In summary,when the KGM substitution rate is higher,the gluten protein molecules of weak gluten wheat probably bind to KGM molecules through hydrogen bonding,which induces the aggregation of small-size GMP particles to form more medium-and large-size GMP particles,and some of the α-helix in gluten proteins are transformed into stable β-sheet structures,This results in a more stable and continuous gluten network structure;In contrast to weak gluten wheat,KGM disrupted the disulfide bonds in the gluten of middle and strong gluten wheat,enhancing the electrostatic repulsion on the surface of gluten molecules and inhibiting the aggregation of gluten protein molecules,resulting in the depolymerization of medium and large size GMP particles and the increase of irregularly curled structures in gluten proteins,destroying the stability and continuity of the gluten structure.This study provides theoretical guidance for the application of KGM in a wide range of pasta products.