Interactions and functionality of fiber components in a directly expanded starch matrix

The interactions of cellulose (2–10%), hemicellulose (1–5%), pectin (1–5%), lignin (1–5%) and a blend of these fibers (5–25%) with cornstarch matrix were studied and the effect of these fibers on properties of cellular extrudates determined. Peak gelatinization temperature increased from 94.3 °C for the starch control to 96.6–103.1 °C with addition of fibers. Extrusion specific mechanical energy decreased on addition of fibers (338 kJ/kg versus 197–308 kJ/kg) with the largest decrease observed for cellulose. Longitudinal expansion increased with addition of fibers (specific length 35 mm/g versus 62–67 mm/g). Addition of pectin led to higher radial expansion (23 versus 24–27), while cellulose caused a decrease (14–23). Microstructure features evaluated using X-ray microtomography were similar for the control and pectin regarding cell size and void fraction, while cellulose caused a different microstructure (2249 μm and 83.7%, respectively, for control; 2334 μm and 89.0% for 5% pectin; 473.3 μm and 72.1% for 10% cellulose). Crushing force was inversely related to cell size. It was concluded that impact of fibers on cellular extrudates was related to compatibility with starch. •Interaction between fiber components and starch leads to differences in extrudates.•Extrudates with starch, lignin, pectin and xyloglucan share microstructural features.•Cellulose drives low expansion in extruded products with cell wall material.