Study of the Effect of extrusion pre-treatment conditions on physico-chemical properties of gluten-free flour blend of rice and corn

Rice and corn flours are appropriate alternatives for developing gluten free products and modification of some of their properties by different processes could be effective for improvement of gluten-free products quality. This study was conducted to study the effect of extrusion process on physic-chemical properties of free-gluten blend flour of rice and corn (1:1 ratio). For this purpose, extrusion treatments with variables of die temperature (110, 145 and 180 °C) and feed moisture (12, 15 and 18 %) were applied and features of water absorption and solubility index, damaged starch, color parameters, bulk density and thermal properties by DSC were investigated. The results showed that applying the extrusion process lead to significant changes in all measured features so that the water absorption, solubility index and damaged starch were increased from 1.88 g/g, 4.5% and 8 UCD in control sample to 4.4-7.1 g/g, 11.4-28.5% and 20.2-28.8 UCD in treated samples respectively, whereas bulk density and lightness were reduced. Study of thermal properties showed that gelatinization temperatures including onset (To), peak (Tp) and conclusion (Tc) temperatures were raised significantly but gelatinization enthalpy (∆E) was decreased. Finally due to occurred changes in flour samples during extrusion process, it could be concluded that this process can be suitable pretreatment for production of flours with different functional properties that may be useful for preparation of various gluten-free products.