Research On Effects Of Inulin And Gluten Interaction On Heat-induced Gluten Gel Quality And Its Mechanism

Adding inulin to cereal products can increase the dietary fiber intake in daily diet,however,the addition of inulin also greatly affected the final quality of cereal products.Just a little attention paid on the other factors such as inulin itself（molecular weight,Mw）,processing conditions（temperature,moisture,acid,alkali,salt ion,etc.）and gluten protein components（gliadin,glutenin）which also affect the qualities of cereal products.Therefore,this paper uesed gluten protein and three kinds of inulins（molecular weight were 419,1020,and 3359 Da,respectively）as the raw material,and the effects of inulin on the physicochemical properties and structure of the gluten protein heat-induced gel were investigated,further the influences mechanism was studied by exploring the effect of inulin on the structure of glutenin and gliadin.The main results are as follows:1.The effect of inulin molecular weight and added amount on the properties of heat-induced gluten gel.The heat-induced gel was formed by compounding inulin（Mw were 419,1020,and 3359 Da,respectively）in different amounts（0,10%,20%,30%,and 40%）with gluten.The rheological properties,texture properties,and structural properties of the gel were studied.The results showed that inulin reduced the gluten protein’s denaturation and cross-linking,but inulin with middle and high Mw finally formed inulin-gluten gel with higher values on G’,G",tanδ.Inulin-gluten gels are soft-textured gel since it had smaller value in hardness,cohesiveness,chewiness and resilience.The water holding capacity of the inulin-gluten protein system decreases with the increase of the molecular weight and the amount of inulin.Inulin reduced the hydrophobic interaction of gel,the ionic bonds and hydrophobic interactions in medium/high-molecular-weight inulin-gluten were reduced but hydrogen bonds were increased.The three types of inulin reduced hydrophobicity index H₀and disulfide bonds of gluten.When inulin was added at 40%,low/medium/high molecular weight inulin reduce H₀ of gluten（17104）to 14594,11869 and 9866,disulfide bonds were reduced by 31.8%,68.1%,and 78.2%,respectively.Addition of inulin resulted in a decrease inβ-sheet and an increase in random coil in of gluten protein.Inulin also changed the disulfide bond conformation of gluten protein from g-g-g to unstable structures.These indicated that inulin caused the structure of gluten to become disordered and unstable.Gel electrophoresis showed that medium/high molecular weight inulin mainly affected the cross-linking and aggregation of gluten components at30-35 k Da.Compared with the gluten gel alone,the inulin-gluten complex gel had weaker structural uniformity and roughness increased since inulin adhered to and filled in the gluten structure.In short,the effect order of inulin on the physicochemical properties and structure of inulin-gluten heat-induced gels was high-molecular-weight inulin>medium-molecular-weight inulin>low-molecular-weight inulin,this was attributed to the large molecular weight change the folding and aggregation of gluten molecules and decreased the hydrophobic interactions and disulfide bonds stronger.2.Study on the mechanism of inulin molecular weight and added amount on gluten gel properties.The effects of different molecular weights（419,1020 and 3359 Da）and different added amounts（0,10%,20%,30%,40%）of inulin on gliadin and glutenin structure after heat-induced were further investigated.The results showed that inulin with three different molecular weights resulted in lower hydrophobicity indexes H₀and less disulfide bonds of glutenin and gliadin.The effect of inulin on glutenin disulfide bonds was greater than that of gliadin,and high-molecular-weight inulin had the strongest effect.The strong interaction between inulin and glutenin caused static quenching of tryptophan but with minimal effect on tryptophan of gliadin.The gel electrophoresis spectrum showed that only high molecular weight of inulin had effect on the 30～35 k Da area of gliadin,but 3 kinds of inulins both reduced the band strength of low molecular weight glutenin subunits.Inulin caused the tyrosine residues of glutenin and glutenin to tend to be embedded in the molecule,which was not conducive to the aggregation of protein molecules.At the same time,inulin can promote the disulfide bond instability of glutenin and glutenin and both of three inulins increased the random coil of gliadin and leaded to a decrease inα-helix orβ-sheet,indicating that inulin can lead to abnormal folding of gliadin.The inulin increasedα-helix andβ-turn of glutenin and reducedβ-sheet and random coil,indicating that the addition of inulin promoted the self-folding of glutenin polypeptide chains and reduced interchain cross-linking.Inulin reduced the homogeneity of the gliadin microstructure and broken the its tight and smooth structure,at the same time inulin adhered to and filled in structure of glutenin to weak and interrupt the glutenin cross-linking,leadig to local structural fracture.The thermal stability of the inulin-gliadin is higher than that of inulin-glutenin,which is also related to the more open and fragile structure of the latter.Inulin had effect both on the structure of gliadin and glutenin,and it had a stronger effect on glutenin.In general,the effect of inulin on gluten protein gel is due to the combined effect of inulin on gliadin and glutenin,and the effect order of three kinds of inulin was:high-molecular-weight inulin>medium-molecular-weight inulin>low-molecular-weight inulin.The effect of inulin on gluten gel depends more on the effect of inulin on glutenin.3.The establishment of data model between inulin molecular weight,added amount and physicochemical properties of gluten gel quality.Using water holding capacity,intermolecular forces,surface hydrophobicity index,and disulfide bond content as indicators to study the influence of inulin molecular weight and inulin addition amount on gluten gel quality.The results showed that the effect of inulin molecular weight,addition amount and interaction on water holding capacity and surface hydrophobicity index was inulin addition amount>inulin molecular weight>interaction,and the effects on other indicators are inulin molecular weight>inulin iddition>interaction.The further establishment of the data model in polynomials of the second and third order between indicators of gel quality and molecular weight x₁ and the added amount x₂.15%high molecular weight inulin was used to verify the equation,and the errors between the predicted and measured values of each index were small.The fitting model had a certain practicability.A comprehensive evaluation index（F）of gel quality and each indicator（X1～X10）were established by principal component analysis,F=-0.106X1+0.24X2+0.023X3+0.284X4+0.036X5-0.089X6-0.105X7+0.216X8+0.04X9+0.148X10.This experiment found that 3 kinds of molecular weight inulin weaken the quality of gluten heat-induced gel,and the effect order was:high molecular weight inulin>medium molecular weight inulin>low molecular weight inulin.Inulin strongly interacted with glutenin and hindered its intermolecular aggregation,Inulin also inserted into the gliadin to destroy its intramolecular folding and intermolecular cross-linking,thus leaded to change on gluten gel interaction forces and the conformation of gluten protein,which weaken the structural stability of gluten gel.In addition,the gluten protein gel texture quality,water holding capacity,protein surface hydrophobicity index,disulfide bonds had been successfully established data model with inulin molecular weight（x₁）and inulin addition（x₂）and these model can be used to predict the effects of inulin on gluten gel.A comprehensive evaluation index of gel quality and each index were established.