Screening of variables for extrusion of rice flour employing a Plackett–Burman design

Turbo-Treatment of Rice Flour to Improve Technological Functionality

Turbo-technology (i.e., a heat/shear treatment) potential in modifying rice flour technological properties (i.e., damaged starch, pasting properties, apparent cold viscosities, and color) depending on cooking temperature (120–200 °C), added water (30–40%), and drying temperature (160–200 °C) was evaluated. Applying a Box–Behnken design, highly significant (p < 0.001) models were found for moisture, damaged starch, pasting properties, and cold viscosities. The most important factor was the added water, significantly (p < 0.001) affecting all treated flour characteristics. The optimization resulted in 200 °C as cooking and drying temperature and 40% added water, but values of damaged starch and cold viscosities in the treated flour were still low. Thus, flour was overnight wetted (40% water) before cooking and drying at 200 °C, obtaining high values of damaged starch (49.5 ± 1.5 g/100 g db) and cold viscosities (from 6213 to 21,436 cP). The study represents a guide for the application of turbo-technology to design flour with tailored technological properties.

The effect of moisture content on physicochemical properties of extruded waxy and non-waxy rice flour

The properties of waxy rice flour (WRF) and non-waxy rice flour (RF) were modified using an extrusion process with different feeding material moisture contents. WRF was more affected by the thermomechanical stress from extrusion; consequently, it had a lower glass transition temperature but higher water solubility index (WSI) indicating higher molecular degradation than extruded RF. The lower moisture content of the feeding flour caused more severe flour damage (coarser surface of the extruded flour) and lowered relative crystallinity compared to higher moisture content processing. Moreover, low moisture content processing led to complete gelatinization, whereas, partial gelatinization occurred in the higher moisture content extrusion. Consequently, the extruded flours had a lower peak viscosity and gelatinization enthalpy but a higher water absorption index and WSI than native flour. In conclusion, the rice flour type and the moisture content of the extrusion feeding flour affected the physicochemical properties of the extruded flour.