Effects Of Freeze–thaw Cycles On The Physical And Structural Properties Of Wheat Gluten With Variations In The HMW-GS At The Glu-B1 Locus

Because the frozen dough technology can be convenient,fast,and maintain the flavor of food for a long time,it has become the preferred preservation method in the baking industry.However,temperature fluctuations or repeated freeze–thaw during the freezing process may deteriorate the processing quality of the frozen dough,and the deterioration of the gluten is a key factor for the deterioration of the quality of the frozen dough.At present,studies on the effects of frozen treatment on the structure and physical properties of glutenin and gliadin and the effects of heat treatment on the unfolding and folding of frozen gluten have been reported.However,the freeze–thaw cycles have little research on the structure and physical properties of gluten of different high molecular weight glutenin subunits?HMW-GS?.In this study,the near-isogenic lines NIL1?1,6+8,2+12?and NIL2?1,14+15,2+12?of the HMW-GS alleles of Glu-B1 locus in the genetic background of Xinong 1718were used as materials to study the effects of freeze–thaw cycles on the physical properties and structure of gluten in near-isogenic lines.The main results are as follows:?1?After repeated freeze–thaw cycles,the freezable water content of the two near-isogenic frozen gluten increased.Compared with NIL1?1,6+8,2+12?containing inferior subunits,NIL2?1,14+15,2+12?with high quality subunits has less increase in freezable water content.This indicates that NIL2?1,14+15,2+12?is more suitable for frozen dough than NIL1?1,6+8,2+12?.?2?Before the freeze–thaw cycles,the thermal denaturation temperature?T_p?,thermal enthalpy??H?and thermal degradation temperature?T_d?of NIL2?1,14+15,2+12?were higher than NIL1?1,6+8,2+12?,and there was no significant difference in weight loss rate?%?.After repeated freeze–thaw cycles,the T_p and weight loss rate?%?of both near-isogenic lines increased,and both?H and T_d decreased.However,the extent of increase and decrease in thermodynamic properties of frozen gluten from NIL2?1,14+15,2+12?was less than that of NIL1?1,6+8,2+12?,indicating that NIL2?1,14+15,2+12?is more stable than NIL1?1,6+8,2+12?under freeze–thaw cycling conditions.?3?There are significant differences in the microstructure of frozen gluten composed of different HMW-GS.The surface structure of the two near-isogenic gluten proteins is relatively intact and smooth before the freeze–thaw cycle.As the number of freeze–thaw cycles increases,the surface structure of the frozen gluten becomes rough,the pores in the network become larger,the number increases,and some small protein fragments can be seen to fall out of the gluten network?especially after the fourth freeze–thaw cycle?.However,after repeated freeze–thaw cycles,the frozen gluten from NIL1?1,6+8,2+12?is more depolymerized than NIL2?1,14+15,2+12?,and the surface structure is also better than NIL2?1,14+15,2+12?is more rough.?4?The freeze–thaw cycle has distinct effects on the surface hydrophobicity of gluten of HMW-GS near-isogenic lines.Under repeated freeze–thaw cycles,the surface hydrophobicity of the frozen gluten of the two near-isogenic lines increased.Compared with the surface hydrophobicity of fresh gluten,the surface hydrophobicity of NIL2?1,14+15,2+12?increased less than that of NIL1?1,6+8,2+12?,indicating that NIL1?1,6+8,2+12?is more sensitive to repeated freezing and thawing than NIL2?1,14+15,2+12?.?5?The disulfide bond?-S-S-?plays a key role in maintaining the tertiary structure and conformation of gluten.As the number of freeze–thaw cycles increased,the-S-S-content of the two near-isogenic lines decreased significantly,while the sulfhydryl?SH₁?content increased significantly,indicating that the freeze–thaw treatment converts-S-S-in the gluten into SH₁.Compared with fresh gluten,the frozen gluten from NIL2?1,14+15,2+12?has a smaller reduction in-S-S-content than NIL1?1,6+8,2+12?,indicating that the GMP depolymerization of NIL2?1,14+15,2+12?is less than that of NIL1?1,6+8,2+12?.?6?The freeze–thaw cycle treatment changes the conformation of gluten.Before the freeze–thaw cycle,the?-sheet structure in the gluten of two near-isogenic lines was dominant,and the content of?-sheet structure of NIL2?1,14+15,2+12?was higher than that of NIL1?1,6+8,2+12?.After repeated freeze–thaw cycles,the content of?-helix and?-turn structure decreased,while the content of?-sheet and intermolecular?-sheet structure increased,indicating that the freeze–thaw cycle caused the protein to aggregate.In addition,the freeze–thaw cycle has a greater effect on the conformation of proteins from NIL1?1,6+8,2+12?than NIL2?1,14+15,2+12?.This indicates that NIL2?1,14+15,2+12?is more stable than the conformation of NIL1?1,6+8,2+12?under freezing and thawing conditions.