Rheology and microstructure of sago starch from Papua New Guinea

The flow properties and microstructure of six sago starch samples from diff erent localities (Kavieng, Kerema, Lae, Lorengau, Madang, and Wewak) in Pap ua New Guinea have been investigated. The rheological behaviour of 4% (w/w) paste was studied at 30 degreesC, 40 degreesC 50 degreesC, 60 degreesC and 70 degreesC, results were presented as shear stress-shear rate data and an alysed using six yield stress and the power-law models. The viscosity was g enerally time-independent (CV = 2-6%) and irrespective of the temperature, shear stress increased with the rate of shear for all the samples (pseudopl astic). The power-law model provided a good estimation (r = 0.8739-0.9979) of the rheological behaviour with its index being 0.38 +/- 0.072 to essenti ally show no dependence on temperature and the source of the starch. The co nsistency index was temperature-dependent and E-a = 9.8-23.0 kJ mol(-1). Sc anning electron microscopy revealed some damaged starch granules but granul e morphology was identical for all the samples. The pH of the samples range d from 3.7-5.1 and samples with low pH were generally of a low consistency index irrespective of the temperature. (C) 2001 Elsevier Science Ltd. All r ights reserved.