As indicated, therewas more reduction in PV of Orbit uji than NS 5511 uji through fortification with cowpea, even though the same proportion of cowpea was used in the preparation of the fortified flours. This suggests that starch content alone may not explain the differences in uji viscosity. The variations in the compositions of the different fermented flour suspensions may have played a role in the differences in observed PV. This is because as already mentioned, the sorghum cultivars possessed different chemical qualities, particularly tannin and protein contents. Protein content has been shown to affect CPV (Zhang & Hamaker, 2003). Proteins may interact with the C-2 and C-3 hydroxyl groups of glucose units through H-bonding and prevent intermeshing of amylose and amylopectin helices (reviewed by Preston, 1998). These proteineglucose
interactions may be an impediment to starch retrogradation, which is normally implicated in the development of CPV. However, the fact that sorghum with higher protein content (NS 5511 e 11.0% protein) had higher CPV than the one with lower protein content (Orbit e 8.4% protein) may be due to NS 5511 sorghum containing tannins. Proteins have a high affinity to bind to sorghum tannins (Hagerman & Butler, 1980), which in the case of NS 5511 sorghum uji, probably facilitated the starch molecules to interact between themselves, resulting in greater retrogradation compared to Orbit sorghum uji starch