Physicochemical properties of extrusion-modified konjac glucomannan

Konjac glucomannan was extruded and subsequently ground under four conditions denoted: KGM1 (33% solids, 90 °C), KGM2 (24% solids, 90 °C), KGM3 (24% solids, 90 °C, die restriction), and KGM4 (24% solids, 110 °C). SEM and particle size analysis showed that extruded KGM had slightly larger and rougher particles. The water absorption index was decreased to 47.92–128.80, as compared to 153.64 for the control (KGMC). The crystallinity index increased to 2.97 and 3.42 for KGM3 and KGM4 samples, as compared to 1.72 for the control. Zero-shear viscosity of 0.5% solutions decreased to 0.36–3.01 Pa s. All samples were shear-thinning and data were best fitted by the Cross model. Based on capillary viscometry, molecular weights were decreased to 2.7 × 105–9.9 × 105, as compared to 1.2 × 106 for the control. In most cases, properties were most altered by higher temperature and shear, and to a lesser extent by lower solids in the feed.