Dextran and its effect on the flow behaviour of molasses and crystallization rate

The rheological studies of final molasses with dextran concentration up to 4%, by weight have been carried out using Brookfield HBDV III Programmable Rheometer with small sample adapter using cylindrical spindle from 40 to 60 degrees C. Molasses indicated pseudo-plastic behavior. Power law model was applied and flow behaviour index and consistency coefficient were evaluated. Flow behaviour index was less than 1 at all temperatures, confirming the pseudoplastic behavior. It decreased further with the addition of dextran indicating the increase in pseudoplasticity. Consistency coefficient has been found to increase uniformly with the addition of dextran up to 3%. On further addition of dextran, consistency coefficient was found to double. It was found to decrease with increase in temperature and nearly halved for every 10 degrees rise in temperature. Arrhenius model was applied to determine the flow activation energy which increased uniformly up to 3% and then there was a sharp rise thereby confirming the results reported earlier. Rates of sugar crystallization have been studied in a 500 cm(3) laboratory vacuum pan at 1.05 and 1.10 super saturation with 1% dextran content at 60 and 70 degrees C and with seed sizes 600 and 850 pm. Three concordant readings gave a maximum error of 0.13%. It can be seen that there is a decrease in rate of crystallization on the addition of dextran. It increased with the increase in super saturation and temperature but decreased with the increase in seed size. (c) 2007 Elsevier Ltd. All rights reserved.