Physicochemical properties of extrusion-modified konjac glucomannan

Konjac glucomannan was extruded and subsequently ground under four conditions denoted: KGM1 (33% solids, 90 degrees C), KGM2 (24% solids, 90 degrees C), KGM3 (24% solids, 90 degrees C, die restriction), and KGM4 (24% solids, 110 degrees 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 Pas. 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 x 10(5)-9.9 x 10(5), as compared to 1.2 x 10(6) 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. (C) 2011 Elsevier Ltd. All rights reserved.