Salt-Induced Disaggregation/Solubilization of Gliadin and Glutenin Proteins in Water (1)
The limited solubility of gliadin and glutenin in water is an important factor in the uniqueness of wheat for breadmaking. As with the gliadins, with positively charged side chain at the slightly acidic pH of normal gluten, and ionizable groups in general, are important factors in accentuating the potential role of ionic interactions and salt effects in the solubility of these proteins in aqueous solvents.
The protein contents for all three glutens were comparable and ranged from 82% for DDW gluten to 86% for 2% NaCl gluten. The PAGE and SDS–PAGE patterns indicated that the three glutens were similar on the basis of subjectively assessed band intensity and qualitatively identical in protein composition.
The percentage of gluten protein extracted by the four DDW extractions was 27·5% for the DDW gluten, 51·7% for the 0·2% NaCl gluten and 84·5% for the 2% NaCl gluten. SDS–PAGE patterns of the glutens and their fractions after reduction with 2-mercaptoethanol clearly showed the presence of HMW subunits of glutenin in all the DDW-soluble fractions of the gluten prepared with 2% NaCl but only very faint bands in the lanes for fractions of DDW gluten.
The slow moving w-gliadins tended to be soluble in both 50% and 70% propan-1-ol, whereas the fast moving w-gliadins were insoluble (along with glutenin) in 70% propan-1-ol. Owing to the small net positive charge of gluten proteins at pH 4·8–5·0, electrostatic repulsion effects would tend to increase gluten protein solubility in DDW, after removal of the salt.