Fermentation modifies protein/protein and protein/starch interactions in sorghum dough

A study was made on the molecular and structural changes occurring in the protein and starch components of sorghum flour when fermented to prepare typical non-malted Sudanese foods. Protein solubility and SDS-PAGE studies indicated that water-soluble proteins are the main target of hydrolysis during fermentation. Proteolysis products are taken up for bacterial growth. Kafirins are among the proteins left intact by proteolytic events in the fermentation step. Upon cooking in boiling water kafirins are converted into protein aggregates almost insoluble even in the presence of 8 M urea and of disulphide-reducing agents. Viscoamylographic and microstructural studies indicate that fermentation leads to the release of starch granules from very compact structures in the original sorghum flour, in which proteolysis-sensitive, water-soluble proteins form an essential part of the outermost shell of large structures, where starch granules are embedded into a kafirin-rich protein matrix that is not affected by proteolytic events during fermentation.