Running head: Waxy and high protein digestibility sorghum 1 HIGHLIGHTS Combined waxy-high protein digestibility traits in sorghum gave high peak viscosity High protein digestibility overrode the waxy trait giving floury endosperm texture Combined waxy-high protein digestibility traits gave high flour water solubility Flour solubility of waxy-high protein digestibility traits was similar to wheat flour 2 AbstractNovel biofortified sorghum lines have been developed with both waxy starch (high amylopectin) and high protein digestibility traits. Eight sorghum lines with different combinations of waxy, non-waxy, high-and normal-protein digestibility traits were studied in relation to flour properties. Lines with the high protein digestibility trait had loosely packed starch granules and floury endosperm, irrespective of whether they were waxy or non-waxy.In terms of thermal properties, waxy-high digestibility lines had the highest onset endothermic temperature as well as endothermic energy compared to non-waxy-normal protein digestibility lines. The waxy-high protein digestibility lines had higher paste viscosity and formed much softer and less sticky pastes than the non-waxy, normal protein digestibility lines. Flours of the waxy-high protein digestibility sorghum lines had much higher solubility than the non-waxy-normal protein digestibility lines. At 30 o C flour solubility, waxy-high protein digestibility sorghum lines flour was similar to commercial wheat bread flours. The high flour solubility, high pasting viscosity and soft paste of sorghum lines with combined waxy and high protein digestibility traits indicates that their flours are likely to produce more functional doughs and hence better quality food products than normal non-waxy, normal protein digestibility sorghums.3

Stable viscoelastic masses have been formed from kafirin in a mainly aqueous system. Kafirin was dissolved in glacial acetic acid (GAA) and simple coacervation was performed by rapid addition of 15°C water under low shear. Kafirin precipitated out as a network of hydrated fibrils which could be hand-kneaded into a viscoelastic mass. These could be formed from a very wide range of kafirins, including those where β- or γ-subclass expression was suppressed. Kafirin composition influenced the appearance of the masses but did not fundamentally affect stress-relaxation behaviour. Fresh kafirin masses exhibited similar elasticity and viscous flow balance to gluten. They maintained functionality when stored for several days at 10°C but their elastic component increased. FTIR showed that when kafirin was dissolved in GAA its α-helical conformation increased substantially. Dissociation of the kafirin molecules in GAA, assuming a α-helical conformation may have enhanced water binding, enabling viscoelastic mass formation.

Arising from work showing that conventionally bred high protein digestibility sorghum types have improved flour and dough functionality, the flour and dough properties of transgenic biofortified sorghum lines with increased protein digestibility and high lysine content (TG-HD) resulting from suppressed synthesis of several kafirin subclasses, especially the cysteine-rich γkafirin, were studied. TG-HD sorghums had higher flour water solubility at 30 o C (p <0.05) and much higher paste viscosity (41% higher) than their null controls (NC). TG-HD doughs were twice as strong as their NC and dynamic rheological analysis indicated that the TG doughs were somewhat more elastic up to 90 o C. CLSM of doughs and pastes indicated that TG-HD had a less compact endosperm protein matrix surround the starch compared to their NC. The improved flour and dough functional properties of the TG-HD sorghums seem to be caused by reduced endosperm compactness resulting from suppression of synthesis of several kafirin subclasses which modifies protein body and protein matrix structure, and to improved protein-starch interaction through hydrogen bonding specifically caused by reduction in the level of the hydrophobic γ-kafirin. The improved flour functionality of these transgenic biofortified sorghums can increase their commercial utility by complementing their improved nutritional quality.