Reactive Extrusion of Sorghum Flour with Ozone Modifies the Texture, Thermal Behavior, and Digestibility of Starch and Proteins

TL;DR

This study shows that using ozone during extrusion changes the texture, water absorption, and digestibility of sorghum flour, offering a sustainable food processing method.

Contribution

The novel contribution is using ozone-assisted reactive extrusion to modify sorghum flour properties in a sustainable and clean-label way.

Findings

Ozone reduced specific mechanical energy and increased extrudate density in sorghum flour.

XPS confirmed oxidation of hydroxyl groups into carbonyl and carboxyl groups.

Ozonation improved protein digestibility but reduced starch hydrolysis in the gastric phase.

Abstract

This study addresses the need for sustainable and clean-label processing methods to enhance the functional and nutritional properties of sorghum flour. Reactive extrusion combining high shear forces and ozonization was selected as an environmentally friendly modification strategy. Whole and polished sorghum flours were processed using a twin-screw extruder, with ozone introduced via ozonated feed water under varying temperature profiles (140 °C and 160 °C) and moisture contents (20% and 23%). Characterization included specific mechanical energy (SME), textural attributes, water absorption and solubility indices (WAI/WSI), viscosity profiles (RVA), and surface chemistry via X-ray photoelectron spectroscopy (XPS). Finally, in vitro digestion was used to monitor the kinetics of starch and protein hydrolysis. Ozone reduced SME, increased extrudate density, and lowered expansion and fracture force, particularly in polished flour. The XPS confirmed successful oxidation, showing the conversion of hydroxyl groups into carbonyl and carboxyl groups. Ozone also improved water absorption but reduced solubility and decreased viscosity parameters in polished flour. In vitro digestion showed that extrusion ozonation enhanced protein digestibility at ~25%. At the gastric phase, ozonized whole samples showed 18.3% starch hydrolysis, and ozonized polished flour showed 8.3%, whereas non-ozonized flours exhibited ~25%. These findings prove that ozone-assisted reactive extrusion differentially changes sorghum flour properties, offering a promising approach for improved food applications.

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