| Abstract
| - Changes in the viscosity properties of γ-irradiated rice starches (from 1 to 25% amylose content)from four genotypes (JY293, Jiayu 293; XS, Xiushui; ZF504, Zhefu 504; and ZXN, Zaoxiannuo) duringpasting in water (pH 7) or in different pH solutions were studied using a rapid visco analyzer. Peakviscosity (PV) of all native rice starches was little affected at pH 4 and 10, while hot paste viscosity(HPV) and cool paste (final) viscosity (CPV) were generally lower at pH 4 and higher at pH 10 ascompared with that at pH 7. The PV, HPV, and CPV of γ-irradiated starches were higher at pH 4 andlower at pH 10 than pH 7. All viscosity characteristics of native rice starches were reduced in strongeralkali (pH 11.5) or acidic (pH 2.5) solutions. However, the γ-irradiated starches were substantiallyhigher at pH 2.5 but lower at pH 11.5, indicating that the effect of irradiation was highly pH dependent.The swelling volume of irradiated ZF504 and JY293 starch at all irradiation levels was higher at pH4 than pH 7, while the values were lowest at pH 2.5. The irradiated ZXN and XS starches had higherswelling volumes at pH 4 and pH 2.5 than pH 7. Differential scanning calorimetry analysis showedthat γ-irradiation caused progressively lower gelatinization peak temperature (Tp) and highergelatinization range (Tr) at pH 7. Tp was higher and Tr was lower at a much stronger acidic condition(pH 1) for both native and irradiated starches. The possibility of using viscosity changes in low pH forthe detection of irradiated starch was discussed. Keywords: Starch; pasting viscosity; γ-irradiation; pH
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