The Importance of Molecular Structure for Textural and Physicochemical Properties of Extruded Wheat Flour.

Abstract

This study elucidated the mechanistic interplay between the extrusion parameters (temperature and screw speed), starch molecular architecture (chain-length distribution), and key physicochemical properties of wheat flour extrudates. Four wheat flours with varied amylose contents were extruded, where the average hydrodynamic radius (Rh-) was reduced by 75.5% in normal wheat (e.g., CM55), while waxy wheat (WW) exhibited higher Rh-. Crispness correlated negatively with long amylopectin branches (36 < X ≤ 100), with WW displaying superior crispness (12.22 N/mm). Short amylopectin chains (X 6-36) increased under thermomechanical stress, enhancing the expansion index (SEI), whereas long chains (X > 100) restricted expansion. Temperature may modulate color difference (Δ<i>E</i>) via Maillard reactions, while higher specific mechanical energy (SME) intensified browning. Higher temperatures (>170 °C), rather than SME, caused significant changes in the proportion of short branches and long branches, with SME exhibiting a negative correlation with Rh-, indicative of substantial molecular degradation. The starch chain-length distribution, rather than amylose content alone, dictates extrudate functionality.