Effects Of Konjac Gum And Artemisia Sphaerocephala Krasch.Gum On The Properties Of Wheat Dough And Its Mechanism

Konjac Gum(KGM)and Artemisia sphaerocephala Krasch.Gum(ASKG)are both natural plant polysaccharides with thickening and cohesion,which not only have excellent physical and chemical properties but also have certain functional properties.Nowadays,more and more reports on the use of KGM and ASKG as food additives are available.The wheat flour is an important food material,and the consumer market is large.Dough and products made by adding KGM and ASKG into wheat flour can change physicochemical properties of products.However,there is a lack of systematic research on its function characteristics and mechanism of action.There are important theoretical and practical values for the study of the characteristics of dough and steamed bread and related mechanisms of dough.This paper firstly focused on the impact of KGM and ASKG on the properties of wheat dough and steamed bread,and then the interactions between hydrocolloids(KGM and ASKG)and the main components of wheat flour were explored,including the effects of KGM and ASKG on the gelatinization and retrogradation of wheat starch and the interaction between these two hydrocolloids and gluten protein.The main research contents were as follows:(1)The effects of KGM and ASKG on the properties of wheat dough and steamed bread:The pasting viscosities and breakdown of wheat flour increased with the addition of KGM and ASKG.Water absorption,the degree of softening C1-C2and development time of dough increased with increasing the concentration of hydrocolloids and decreased the setback C5-C4,while KGM weakened the stability time of dough and the addition of ASKG were found a reverse trend.The parameters of extensograph properties(resistance to extension,extensibility and energy)were found a dreasced trend.There was no significant effect(P>0.05)in extensograph properties of dough with ASKG.The addition of KGM and ASKG in dough resulted in weaker storage modulus(G’)and loss modulus(G″)during frequency sweep.The addition of KGM and ASKG disrupted the gluten network structure in dough,which could be observed by scanning electron microscope(SEM).The specific volume was decreased when the steamed bread added with 0.6%-1.0%KGM,while there was no significant effect in specific volume with the addition of ASKG(P>0.05).KGM and ASKG did not affect the brightness and whiteness of steamed bread.Texture analysis showed that the addition of KGM decreased the hardness of steamed bread,while the addition of ASKG increased the hardness.During storage,the hardness of steamed bread with or without KGM and ASKG increased and its edible quality gradually decreased,while adding 0.6%-1%KGM or ASKG could delay the aging of steamed bread.Sensory evaluation results showed that the steamed bread with addition of0.2%-0.6%KGM or ASKG was still acceptable.(2)The effects of KGM and ASKG on the properties of wheat starch:Compared with the control,KGM and ASKG addition increased pasting viscosity of the composite system(P<0.05),and more effect of KGM on pasting characteristics of the wheat starch were found.A decrease in leached amylose of wheat starch was observed with increase in KGM and ASKG level,while KGM and ASKG significantly enhanced the swelling power of wheat starch(P<0.05).The addition of KGM and ASKG in wheat starch increased the consistency index K and decreased the flow behavior index n.Storage modulus(G’)and loss modulus(G″)of the wheat starch were observed to increase during frequency sweep when KGM and ASKG were present,and adding KGM was more effective than adding ASKG in increasing G’and G’.SEM showed that the structures of starch gel were compact with adding KGM and ASKG.Additionally,this phenomenon was more obvious when addition KGM.The dynamic time sweep demonstrated the short-term retrogradation of wheat starch with KGM and ASKG was remarkably inhibitive.The hardness of starch gels with KGM was decrease,while the gels of ASKG had a high level of hardness.Retrogradation enthalpy of all starch gels increased with the increase in storage time at 4°C.Compared with the control,the addition of KGM and ASKG decreased the retrogradation enthalpy of starch gels.It implied that the retrogradation of wheat starch increased during cold storage,while the addition of KGM and ASKG could hindered the long-term retrogradation of wheat starch,and KGM was more effective in inhibiting the long-term retrogradation of wheat starch.After 7 d of cold storage at4°C,X-ray diffraction results exhibited that the relative crystallinity of retrograded wheat starch decreased with the addition of KGM and ASKG,and the addition of0.5%KGM or ASKG had the most obvious effect on wheat starch retrogradation.Fourier transform infrared spectroscopy(FTIR)suggested that there was no new group formation between both hydrocolloids and wheat starch,the main force was the hydrogen bonding and the force was enhanced after the addition of KGM and ASKG.(3)The effects of KGM and ASKG on the properties of wheat gluten:The water binding capacity increased with the addition of KGM and ASKG.The addition of KGM and ASKG reduced G’and G″of gulten which indicated a softening effect in the gluten.The KGM and ASKG samples exhibited a higher content ofβ-turns and free SH,and a lower percentage ofβ-sheets which suggested the worse stability and ordered structure of gluten,the effect of KGM on gluten was more obvious in these changes.The denaturation temperature T_d and thermal enthalpy?H of gluten decreased and the surface hydrophobicity increased in the presence of KGM and ASKG,which suggested that KGM and ASKG reduced the thermal stability and aggregation of gluten.The effects of KGM were more pronounced than that of ASKG.The results of ultraviolet absorption spectra and intrinsic fluorescence spectra suggested that the structure of gluten was unfolded with addition of KGM and ASKG.SEM showed that the KGM and ASKG made the gluten structure disorder and loose,of which ASKG had less effect on gluten than KGM.