Modification of zein dough functionality using kafirin as a coprotein.

Kafirin, sorghum prolamin, was investigated as a coprotein for zein as visco-elastic masses and in starch-based model doughs. Regular kafirin and kafirins from waxy and high protein digestibility (HD) sorghum crosses were studied. HPLC revealed that waxy-HD kafirin was of smaller molecular size and low in β-kafirin. It also had greater surface hydrophobicity. Kafirin addition to zein increased visco-elastic mass elasticity up to ≈50% stress-recovery, similar to wheat gluten. Waxy-HD kafirin gave the highest elasticity, possibly due to its hydrophobicity. Kafirin inclusion at 2:8 parts zein increased the tensile strength of model doughs. Maximum strength was, however, only 60% that of gluten-based dough. Kafirin from regular sorghum gave the highest strength, possibly because of greater disulphide-bonded polymerisation. Confocal laser scanning microscopy showed that zein-kafirin copolymers formed fairly linear fibrils in stretched doughs, indicating excellent compatibility between the proteins. Future research should establish how kafirin-zein copolymer performs in non-wheat flour products.