Battle of the starches: Insoluble versus soluble at the refinery

Authors: Cole, Marsha; Eggleston, Gillian; THOMPSON, JACK - Louisiana Sugar Refining; RATHKE, THOMAS - Imperial Sugar Co; NAIKI, JUNE - American Sugar Refining, Inc; Triplett, Alexa; Zatlokovicz Iii, John

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/15/2015
Publication Date: 8/15/2015
Citation: Cole, M.R., Eggleston, G., Thompson, J., Rathke, T., Naiki, J., Triplett, A., Zatlokovicz, J. 2015. Battle of the starches: Insoluble versus soluble at the refinery. In: Proceedings of the International Sugar Industry Technologists (SIT) Conference, May 17-20, 2015, Osaka, Japan. p.184-208.

Interpretive Summary: In recent years, starch impurity concentrations in U.S. raw sugars manufactured from sugarcane have generally increased and have been persisting into raw and refined sugars. This has led to difficult raw sugar filtration and inefficient carbonatation reactions. Thus, special attention has been focused on revisiting the contributions of several raw sugar quality parameters, specifically insoluble and soluble starch form, on raw sugar filterability at the refinery. Using simulated models, it was found that insoluble starch clogs membrane filters and soluble starch may facilitate filterability; however, both starch forms adversely affect carbonatation reaction chemistry. As insoluble starch detrimentally affects refinery throughput, we are currently developing factory methods to analyze insoluble and soluble starch content in raw sugars as well as their corresponding carbonatation filterability.

Technical Abstract: A study using the USDA starch research method has been conducted to evaluate the effects of total, insoluble, and soluble starch on raw sugar filterability and viscosity in international carbonatation refineries. Raw sugar qualities, i.e., pol, color, % invert, ash, and dextran, were also studied in forty-two international raw sugars supplied by three U.S. refineries, which included two “good” and two “poor” filtering raw sugars with known carbonatation performance. For two “good” and two “poor” raw sugars, total starch by the ICUMSA GS1-17 did not correlate with filterability behavior. The current 250 ppm starch limit in the USA may be too low. More insoluble starch (87%) was present in “poor” filtering raw sugars than in “good” filtering (<64%) raw sugars and had strong correlations to filterability (R=-0.98). A filterability index (FI=0.59) for all forty-two raw sugars distinguished filtering quality of raw sugars, in which FI<0.59 indicated “poor” filterability. High amounts of insoluble and swollen starch content in raw sugars rapidly clogged filters, reduced filtration rates, and increased viscosity of simulated melt liquors and were attributed to filtration problems at the carbonatation refinery. In strong contrast, soluble starch did not affect melt liquor filterability and even facilitated it. Filterability of melt liquors containing 250 ppm total starch and 55% insoluble and 45% soluble starch, was dramatically reduced possibly because it formed macro-colloids that also coated and clogged the press cloth filters as well as inhibited CaCO3 crystallization. New factory methods are urgently needed that accurately measure insoluble starch content in raw sugars and predict their filterability performance for carbonatation refining. Further research is also needed to understand CaCO3 crystal size and formation in carbonated liquors containing soluble and insoluble starch.