Grain of high digestible, high lysine (HDHL) sorghum contains kafirins which enhance the protein network of composite dough and bread

Abstract

The aim of this study was to determine whether protein body-free kafirins in high digestibility, high-lysine (HDHL) sorghum flour can participate as viscoelastic proteins in sorghum-wheat composite dough and bread. Dough extensibility tests revealed that maximum resistance to extension (g) and time to dough breakage (sec) at 35 °C for HDHL sorghum-wheat composite doughs were substantially greater (p < 0.01) than for normal sorghum-wheat composite doughs at 30 and 60% substitution levels. Functional changes in HDHL kafirin occurred upon exceeding its Tg. Normal sorghum showed a clear decrease in strain hardening at 60% substitution, whereas HDHL sorghum maintained a level similar to wheat dough. Significantly higher loaf volumes resulted for HDHL sorghum-wheat composites compared to normal sorghum-wheat composites at substitution levels above 30% and up to 56%, with the largest difference at 42%. HDHL sorghum-wheat composite bread exhibited lower hardness values, lower compressibility and higher springiness than normal sorghum-wheat composite bread. Finally, HDHL sorghum flour mixed with 18% vital wheat gluten produced viscoelastic dough while normal sorghum did not. These results clearly show that kafirin in HDHL sorghum flour contributes to the formation of an improved protein network with viscoelastic properties that leads to better quality composite doughs and breads.