A A C C   2 0 0 0   A n n u a l   M e e t i n g

Addition of sorghum flour to wheat flour negatively affects its dough rheological properties especially when levels increase above 15% sorghum flour. Although there are marked differences in chemical composition of sorghum prolamins, kafirins, compared to wheat gluten that would imply poor functionality in breadmaking systems, kafirins are also unavailable due to encapsulation in protein bodies. The objective of this study was to determine the potential role of kafirin in breadmaking through the use of analogous protein body-free maize prolamin, zein, in a composite flour system. Dough rheological properties, loaf volume and protein network microstructure were examined. Results showed that above its glass transition temperature, protein body-free zein significantly (p<0.01) improved the dough rheological properties and loaf volume of the sorghum-wheat composite flour dough. Dough extensibility and loaf volume increased with increasing amounts of added zein. Microstructural studies to determine the interaction between zein and gluten proteins in the dough and bread systems were done using confocal laser scanning microscopy. Autoflourescence and immunolocalization techniques were used to locate gluten and zein, respectively. Results showed that zeins form networks which tend to coat the gluten matrix in the form of thin fibrils thereby strengthening the dough. This type of microstructure was able to withstand the pressure exerted by gas cell expansion during yeast fermentation resulting in increased loaf volume.