How does temperature govern mechanisms of starch changes during extrusion?

• Published in: Carbohydrate polymers 2018-03, Vol.184, p.57-65
• Main Authors: Logié, Nicolas, Della Valle, Guy, Rolland-Sabaté, Agnès, Descamps, Nicolas, Soulestin, Jérémie
• Format: Article
• Language: English
• Subjects: Chemical Sciences; Crystal; Granule; Pea; Polymers; Potato; Specific mechanical energy; Suspension
• ISSN: 0144-8617; 1879-1344
• DOI: 10.1016/j.carbpol.2017.12.040

Graphical abstract for Logie et al. ’s : proposed scheme for starch melting during extrusion. [Display omitted] •Starch melting during extrusion can be envisioned like a suspension.•Solid particles may be ghost granules or crystalline fragments.•The larger amylopectin content of potato starch enhances macromolecular degradation.•Calorimetric melting temperature partially controls starch melting in extruder.•Mechanical energy contributes to melting by solid friction, at low moisture content. Potato and pea starches were processed on a twin-screw extruder under various moisture and thermomechanical conditions, chosen to keep material temperature Te close to starch melting temperature, Tm, whilst avoiding die expansion. Extruded rods were analysed by asymmetrical flow field flow fractionation coupled with light scattering, X-ray diffraction, DSC, and light microscopy with image analysis. Molar mass of extruded materials decreased more for potato than for pea starch, when specific mechanical energy SME increased, likely because of larger amylopectin sensitivity to shear. No crystallinity was detected when ΔT = (Tm-Te) ≤ 0. Residual gelatinization enthalpy ΔHg decreased with ΔT. As illustrated by larger ΔT values for ΔHg = 0, decreasing moisture favored melting, likely by increasing solid friction. The fraction of granular remnants of potato starch was inversely correlated to SME. These results could be explained by considering starch melting during extrusion as a suspension of solid particles embedded in a continuous amorphous matrix.