Effects of granular structures on the pasting behaviors of starches

Japonica (Tainung 67 [TNu67]) and waxy (Taichung 70 [TCW70]) rice, normal and waxy corn, and cross-linked waxy rice and corn starches were used in an investigation of the influence of the granular structure on the pasting behavior of starch, using small amplitude oscillatory rheometry. Both normal corn and normal rice (TNu67) starches had the highest storage moduli (G'), followed by their cross-linked versions; native waxy corn and rice starches had the lowest. Native waxy starches showed paste characteristics (G' < 500 Pa; tan delta > 0.2) at concentrations of up to 35%. However, cross-linked waxy starches exhibited gel behavior at 10% concentration (cross-linked TCW70) or higher (cross-Linked waxy corn starch). The degrees of swelling power were in the order: TCW70 > native waxy corn > TNu67 congruent to cross-linked TCW70 congruent to normal corn congruent to cross-linked waxy corn starches. Solubilities were in the order: normal corn > TNu67 > native waxy > cross-linked waxy starches. The addition of 2% purified amylose from indica rice (Kaohsiung Sen 7) did not induce gelation of waxy corn starch. Swelling powers of normal corn, TNu67, and crosslinked waxy starches were similar, but normal corn and TNu67 had much higher G' value. Such results implied that the formation of gel structure war governed by the rigidity of swollen granules and that the hot-water soluble component could strengthen the elasticity of the starch gel or paste.