Impact of flour particle size and autoclaving on β-glucan physicochemical properties and starch digestibility of barley rusks as assessed by in vitro assays

Inactivation of Endogenous Rice Flour β-Glucanase by Microwave Radiation and Impact on Physico-chemical Properties of the Treated Flour

“…A pronounced decrease in specific viscosity over time was observed with the untreated rice flours, corresponding to an average activity value of (0.109 ± 0.005)/h, which denotes a high β-glucanase activity in untreated rice flour, only slightly smaller than that reported previously for barley flours, i.e., 0.143 or 0.117 for coarse or fine barley flours, respectively (Lazaridou et al 2014). However, for the microwave-treated flours, the decline in specific viscosity of the mixed standard BG solution-flour extracts over time was significantly smaller (p < 0.05), implying that the hydro-microwave treatment brought about a large reduction in β-glucanase activity of the rice flours; the effect being more pronounced when the time of the treatment and the moisture content of flours increased (see Table 1).…”

“…For the same periods of MW treatment, residual β-glucanase activities were still measured in flours with 13 and 16 % moisture contents, even though they were reduced by 87 and 91 % with respect to the initial flour enzymatic activity. Lazaridou et al (2014) also found that increasing the moisture content of barley flours before hydrothermal treatment by autoclaving, resulted in complete inactivation of the endogenous barley β-glucan hydrolyzing enzymes. This behavior could be explained by the large reduction of the denaturation temperature of proteins even with a slight increase of moisture content in low moisture protein systems (Arntfield et al 1990), such as hydrated flours.…”

“…The β-glucanase activity in control and hydrothermally treated rice flours was assessed by measuring the rate of decrease in specific viscosity of a dilute solution of a pure β-glucan preparation, following addition of flour extracts, according to the method reported in a previous work (Lazaridou et al 2014). The flour extracts were obtained by aqueous extraction (flour/water 1:10) under stirring at 25°C for 30 min and subsequent centrifugation at 2500g for 20 min.…”

“…Some of the methods previously used to inactivate β-glucanase activity are autoclaving, scalding, oven heating, and ethanol refluxing (Lazaridou et al 2014;Rieder et al 2015;Moriartey et al 2010). However, there is no literature information on the use of microwave heating for inactivation of β-glucanase enzymes.…”

“…In other heat treatments of flours (e.g., autoclaving), hydration has been identified as a critical parameter for successful β-glucanase inactivation in barley flours (Lazaridou et al 2014); only in flours with the highest moisture content was there a full destruction of this enzyme. Taken this into account and the fact that the principle of microwave heating is mainly based on water molecule polarization, a study of the effect of rice flour moisture content on β-glucanase inactivation kinetics by MW seemed to be necessary.…”