Genetic diversity in properties of starch from Zimbabwean sorghum landraces

Starch was isolated from 95 sorghum landraces from Zimbabwe using an alkali steep and wet-milling procedure. The physicochemical properties of sorghum starch were examined for potential use in Southern Africa. All the landraces evaluated had a normal endosperm indicated by the amylose content of the starches. Starch properties were not correlated to most of the physical grain quality traits evaluated. Grain hardness was weakly correlated to starch gel adhesiveness (r = 0.36) and amylose content (r = 0.38) (P < 0.001). The mean peak viscosity (PV) of the sorghum starches was 324 Rapid Visco Analyser units (RVU) compared with 238 RVU in a commercial corn starch sample; PV was 244-377 RVU. Some landraces had low shear-thinning starches, implying good paste stability under hot conditions. Pasting properties were highly correlated among the sorghum starches. The starch gel hardness showed considerable variation (44-71 g) among the landraces. Gelatinization peak temperatures were 66-70C. The thermal properties of starches were not correlated with starch swelling and pasting properties. Genotype grouping by highest and lowest values in each category would allow selection of sorghums based on a specific attribute depending on the desired end use.