Effect of rice flour ultrafine particle size on β-glucanase inactivation by microwave treatments and pasting properties in treated flours

Abstract

The main problem in developing gluten-free products enriched with β-glucans (BG) is the hydrolysis they suffer due to the endogenous β-glucanase content of raw materials. The depolymerization causes a decrease in the molecular weight and viscosity, which is the most important parameter related to the health claims of BG. Hence, it is necessary to inactivate the β-glucanase. Therefore, this study aimed to inactivate the β-glucanase activity present in rice flour (Indica variety) with fine particle size using the microwave (MW) hydrothermal treatment method. The rice flour was conditioned at three different humidities 13, 16, 19 and 25%. Samples of 50 g were subjected to different microwave treatments 1, 2, 4 and 8 min, at 900 W power at 20 seconds intervals of treatment and 1-minute rest. The effect of particle size on inactivating the β-glucanase activity and the effect of MW treatment on the flour pasting property were also studied. The inactivation process followed a first-order kinetic response, and the apparent rate constant of thermal inactivation increased exponentially with the moisture content (M) of the flour, according to the equation -0.02t·exp (0.19·M) (R2 = 0.987). Among the treatments employed 4 min treatment at 25% initial M was found effective for complete β-glucanase inactivation. The effect of flour particle size did not show a significant (p> 0.05) difference on the efficiency of β-glucanase inactivation. Keywords: particle size, β-glucans, rice flour, microwave treatment, β-glucanase activity.