Alkali-Induced Protein Structural, Foaming, and Air–Water Interfacial Property Changes and Quantitative Proteomic Analysis of Buckwheat Sourdough Liquor

In this study, the protein structural, foaming, and air–water interfacial properties in dough liquor (DL) ultracentrifugated from buckwheat sourdough with different concentrations of an alkali (1.0–2.5% of sodium bicarbonate) were investigated. Results showed that the alkali led to the cross-linking of protein disulfide bonds through the oxidation of free sulfhydryl groups in DL. The alterations in protein secondary and tertiary structures revealed that the alkali caused the proteins in DL to fold, decreased the hydrophobicity, and led to a less flexible but compact structure. The alkali accelerated the diffusion of proteins and decreased the surface tension of DL. In addition, the alkali notably improved the foam stability by up to 34.08% at 2.5% concentration, mainly by increasing the net charge, reducing the bubble size, and strengthening the viscoelasticity of interfacial protein films. Quantitative proteomic analysis showed that histones and puroindolines of wheat and 13S globulin of buckwheat were closely related to the changes in the alkali-induced foaming properties. This study sheds light on the mechanism of alkali-induced improvement in gas cell stabilization and the buckwheat sourdough steamed bread quality from the aspect of the liquid lamella.