Dynamics of rapid starch gelatinization and total phenolic thermomechanical destruction moderated via rice bio-extrusion with alpha-amylase activation

Abstract

The simultaneous extrusion and enzymatic hydrolysis (bio-extrusion) processing of starchy food materials shows better bioaccessibility of various bioactive compounds, while its mechanism as well as the conditions controlling it are still undetermined for industrial application. The aim of this study was to investigate the influence of bio-extrusion on the kinetics of total phenolics as rapid starch gelatinization occurred. Glutinous rice was primarily extruded with/without thermostable α-amylase (0–1‰) at different feed rates (F, 1.5–3.0 kg h⁻¹), screw speeds (N, 100–200 rpm), moisture content (M, 22–38%) and barrel temperature (T, 80–100 °C). High-efficiency enzymatic extrusion (with F and N as independent variables) was then conducted using response surface methodology when controlled T and M were consistently stable for enzymatic activity. F, N, M and T all affected the degradation rate constants of phenolics (k_P) and starch (k_G). The original positive relationship between k_P and k_G was inverted when amylase was introduced into the extrusion process. The activation energy (E) of total phenolic destruction increased from 37.49 to 70.30 kJ mol⁻¹, mainly because of the great decrease in die pressure, special mechanical energy and shearing action caused by the enzymatic hydrolysis of starch.