Experimental and modeling studies of the flow, dynamic and creep recovery properties of pearl millet starch as affected by concentration and cultivar type

Abstract

Starch from pearl millet varieties viz. ProAgro 9444 and HHB 67, selected on the basis of amylose content was studied for steady, dynamic and creep recovery characteristics as affected by concentration (3–15%). ProAgro 9444 and HHB 67 possess amylose content of 20.21% and 15.05%, respectively. Starch gel exhibited shear thinning behavior with flow behavior index <1, well described by Herschel Bulkley model (R2 > 0.969) at all the concentrations. The starch pastes were thixotropic and the extent increased with increasing concentration and amylose content. Dynamic shear properties obtained within the linear viscoelastic region suggested weak gel like behavior at all concentrations, except 3% starch from HHB 67 which was categorized as dilute solution. Weak gel like behavior at other concentrations was supported by tan δ < 1, and the gel from ProAgro 9444 was more elastic. Power law analysis of data from mechanical spectra also reflected weak gel behavior except for 3% HHB 67. High amylose and increasing concentration favored gel formation as magnitude of temperature at peak G′ and G″ were lower. Creep compliance followed Burger model at higher concentrations whereas 3% HHB 67 exhibited Newtonian behavior. The strain recovery increased with increase in starch concentration and amylose content.