Heat and edible salts induced aggregation of the N-terminal domain of HMW 1Dx5 and its effects on the interfacial properties

Abstract

The gas retention capability of dough is closely related to the terminal domains of high molecular weight glutenin subunits (HMW-GS) in gluten. In this work, the N-terminal domain of HMW-GS 1Dx5 (1Dx5-N) of hydrophobic nature was expressed in E. coli. Its aggregation induced by heating (37 °C, 50 °C, 65 °C, 80 °C) and edible salts (NaCl, Na2CO3) was systematically investigated using circular dichroism, dynamic light scattering and size exclusion HPLC as major tools. The results revealed that heating with NaCl induced the formation of macro-molecular weight 1Dx5-N aggregates (» 670 kDa) through disulfide bond (SS) and hydrophobic interactions. Whereas heating with Na2CO3 under alkaline pH broken the S-S bonds and decreased protein surface hydrophobicity, leading to the formation of relatively low-molecular aggregates (44.3–670 kDa). The interfacial property studies by tensiometry and rheometry suggest that the macro-molecular weight aggregates (» 670 kDa) negatively impacted protein capacity to reduce surface tension, nevertheless this greatly improved the formation of “gel-like” structure at the air/water surface, which would be beneficial for the gas-retention ability of wheat dough. The low-molecular aggregates (44.3–670 kDa) efficiently reduced the surface tension of 1Dx5-N, but led to the weakened interfacial layer, which could be detrimental for the gas-retention of dough. This work is the first to reveal functional difference of heating with table salt (NaCl) and alkaline salt (Na2CO3) in the aggregation behavior and interfacial properties of the N-terminal domain of HMW-GS. This research will provide new insights into the gas retention capability of the N-terminal domain of HMW-GS.