Effects of different extrusion temperatures on physicochemical, rheological and digestion properties of rice flour produced in a pilot‐scale extruder

Abstract

This research was to study the effects of different die temperatures (125, 135, 145, 155, 165 °C) on the physicochemical, rheological, structural properties and in vitro digestion characteristics of extruded rice flour. In this work, the moisture content of feed rice flour was controlled at 18% (w/w, on a dry basis). A twin-screw with 65 mm diameter was used. Feed rate and screw speed were set at 120 kg h −1 and 120 rad min −1 respectively to control variables. The results indicated that the water solubility index improved but the water absorption index reduced at a higher temperature. The total starch content reduced as the temperature increased, but the amylose content was insusceptible to the temperature. Average particle size significantly decreased after extrusion due to the damage of starch granules. The water dispersion system of the extruded rice flour possessed more liquid characteristics than that of raw rice flour. Steady shear analysis revealed that the flow was in a shear thinning behaviour, and apparent viscosity was improved by extrusion but negatively related to extrusion temperature. Crystal type of starch turned from A to V after extrusion. The interaction among rice flour components was mainly noncovalent and could be enhanced by extrusion. The ratio of 1047/1022 cm −1 reflected that the ordered structure was destroyed by extrusion, which was further confirmed by the differential scanning calorimeter result. In addition, the digestibility of extruded rice flour was improved. The in vitro digestibility of protein increased from 75.77% to 86.44% and resistant starch content significantly decreased as extrusion temperature increased.

Physicochemical and structural properties and digestibility of rice flour with different moisture extrusion cooking

“…The sample preparation was referred to our previous research (Lai et al ., 2022) with some modifications. Rice (Northeast Japonica rice, polished) was commercially acquired in a local supermarket and then characterised.…”

Effect of extrusion cooking on the chemical and nutritional properties of instant flours: a review

“…The extrusion temperature constitutes one of the principal factors responsible for the gelatinization of available starches, causing the loss of their crystalline structure and the fragmentation of amylose and amylopectin chains due to the thermo-mechanical impact of the screw. This facilitates amylase accessibility during digestion (Lai et al, 2022). Conversely, increasing moisture content during the extrusion process reduces the mean residence time of the material inside extruder, resulting in higher quantifications of SDS and RS than RDS content.…”