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-degrees for the starch control to 96.6-103.1 C-degrees 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 mu m and 83.7%, respectively, for control; 2334 mu m and 89.0% for 5% pectin; 473.3 mu m 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.