Some physical and chemical properties of starch isolates of cassava genotypes

Cassava starches (Manihot esculenta Crantz) were prepared from tubers of Kaesetsart 50 (KU50), Rayong 5, Hanatee and KIMUL 36-YOO2 (YOO2) and their physicochemical properties studied using the Rapid Visco Analyser (RVA), differential scanning calorimetry (DSC) and rheometry. Amylose content was determined by iodine potentiometric titration (IPT) and gel permeation chromatography (GPC). Starch contents of the tubers varied from 34.2 to 35.1% and protein and fiber contents in the starches varied from 0.8 to 1.1% and 0.6 to 0.8%, respectively. The cassava starches contained 0.06-0.12% lipid and 0.7% to 0.9% ash. Amylose content determined by IPT (15.9 to 22.4%) had higher positive correlation with peak viscosity, breakdown and gel consistencies (R-2 = 0.835, 0.772, 0.859), respectively, whereas GPC (18.1 to 25.3%) showed high correlation with setback (R-2 = 0.923) and DeltaH (R-2 = 0.579). The onset gelatinization temperatures varied from 59.7-64.4degreesC, and KU50 exhibited highest DeltaH of 13.7 J/g. Hanatee and YOO2 formed clear gels with higher peak viscosities, setback and gel consistency viscosities attributed to their higher amylose contents. Retrogradation of KU50 and Rayong 5 tended to be more severe on cooling and formed opaque gels, showing higher resistance to shearing, properties attributed to recrystallized amylopectin fractions.