Effect of radio frequency heating on structure and physicochemical properties of protein and starch based on gelatinization degree of rice flour

As a key ingredient in gluten-free foods, rice flour faces processing challenges due to the absence of gluten. Radio frequency (RF) heating has shown potential to enhance rice flour quality by modulating gelatinization. However, the dynamic evolution of physicochemical properties and the associated structural transitions during RF-induced gelatinization remain unclear. Therefore, this study investigated effects of RF treatment at 6 target temperatures (34, 39, 48, 54, 63, and 72 °C) under the corresponding gelatinization degree (GD) levels (15 %, 30 %, 45 %, 60 %, 75 %, and 90 %) on structures and physicochemical properties of protein and starch in rice flour. Results showed that physicochemical properties and structural changes of rice flour were closely associated with the GD during RF-induced gelatinization. With increasing GD of rice flour, functional properties (swelling power, foaming capacity, and emulsifying capacity), pasting viscosity (peak, trough, and final viscosity) and nutritional components (total protein, crude fat, and amylose content) showed a trend of increasing first and then decreasing, peaking at moderate gelatinization (45 or 60 % GD) levels. Structural analysis revealed that the increased GD of rice flour promoted protein aggregation on the surface of starch particles, reduced values of short-range ordered structure, relative crystallinity, and enthalpy values, and altered secondary and tertiary structures of proteins. This study may elucidate the correlation mechanism between structure and performance during RF-induced gelatinization, providing a theoretical basis for the application of RF technology in the modification of gluten-free rice flour.