Functional properties of normal, waxy and sugary corn starches

Starches separated from different varieties of normal, waxy and sugary corn (Zea mays) were investigated for their physico-chemical, thermal, morphological, pasting and gel textural properties. Sugary corn starch (SCS) showed higher amylose content as compared to normal corn starch (NCS). Swelling power, solubility, water binding capacity (WBC) and transmittance followed the order: waxy>normal>sugary corn starch. Enthalpy of gelatinization (ΔH_gel), enthalpy of retrogradation (ΔH_ret) and percentage of retrogradation (R) followed the order: waxy>normal>SCS. The transition temperatures (T_o, T_p, and T_c) for gelatinization and retrogradation for normal, waxy and SCS did not show significant variation. Normal and waxy corn starches (WCS) displayed smooth surface granules having spherical or angular shape whereas, SCS showed rough surface granules with irregular shape consisting of lobes. Peak-, trough- and breakdown viscosity were in the order: waxy>normal>SCS. Pasting temperature of waxy varieties was lower than the NCS. Hardness, gumminess, chewiness and adhesiveness of the starch gels were in the order: normal>sugary>WCS. Amylose content was negatively correlated to swelling power, solubility and WBC (r= -0.947, -0.776, -0.961, respectively, p<0.01) whereas, it was positively correlated to hardness and gumminess (r= 0.763, 0.690, respectively, p<0.01). T_p was negatively correlated to setback viscosity (r= -0.721, p<0.01); %R was positively correlated to peak- and breakdown viscosity (r= 0.808 and 0.847, respectively, p<0.01). Peak viscosity was positively correlated to trough-, breakdown- and final viscosity (r= 0.957, 0.889 and 0.857 respectively, p<0.01).