Optimal silver nitrate concentration to inhibit α-amylase activity during pasting of rice flour

Endogenous α-amylase interferes with accurate determination of the pasting properties of cereal flour. Silver nitrate (AgNO₃) solutions at seven different concentrations (0.001-0.1 m) plus a deionized water (dH₂O) control are compared for their ability to inhibit α-amylase activity during gelatinization of rice flour with medium to high amylose content (AC). Pasting properties are assessed using a Rapid Visco Analyzer (RVA). The optimal concentration of AgNO₃ to inhibit α-amylase in the flour of rice cultivar Doongara during gelatinization is 1% (w/v) (≈0.06 m). This concentration is tested further in three other types of rice for confirmation of the effects on RVA pasting properties. Peak viscosity is significantly higher using 1% AgNO₃ than in the dH₂O control, while breakdown and pasting temperature are significantly lower. In conclusion, the incorporation of 1% (w/v) AgNO₃ into samples for RVA inhibits the α-amylase activity in rice flour with medium to high AC, allowing pasting properties to be accurately measured using an RVA.