How the physical forms of starch affect filterability at a carbonatation refinery. Part I: Filterability of industrial sugars

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

Submitted to: International Sugar Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2016
Publication Date: 3/1/2016
Citation: Cole, M.R., Eggleston, G., Borges, E., Thompson, J., Rathke, T., Naiki, J., Triplett, A. 2016. How the physical forms of starch affect filterability at a carbonatation refinery. Part I: Filterability of industrial sugars. International Sugar Journal. 118:204-213.

Interpretive Summary: Concentrations of starch, an impurity extracted with sugarcane juice, in U.S. raw sugars have generally increased in the last decade. Insoluble starch (precursor to swollen starch) negatively affects filtration by coating and clogging filter pores while soluble starch was actually found to facilitate filtration. It was found that both an abundance of insoluble starch and total starch concentrations are adversely involved in the mechanical and physical aspects of carbonatation filtration at the refinery; whereas, other soluble raw sugar impurities are indirect measures of “poor” filterability and likely interfere with carbonatation reactions at the refinery preceding filtration. New refinery methods are urgently needed to accurately measure both soluble and insoluble starch content in raw sugars and to predict the filterability performance of raw sugars at the refinery.

Technical Abstract: A study using the USDA starch research method was conducted to evaluate the effects of total, insoluble, and soluble starch on raw sugar filterability and viscosity. Sugar quality parameters, i.e., pol, colour, invert, ash, and dextran, were measured in fifty-five international raw sugars supplied by three U.S. refineries, which included two “good” and two “poor” filtering raw sugars with known carbonatation filtration performance, and three Brazilian factories. Total starch by the ICUMSA GS1-17 method did not predict the carbonatation filterability behaviour of the two “good” and two “poor” filtering raw sugars, and the current 250 ppm starch limit by this method in the USA may be too low. More insoluble starch was present in “poor” (87%) than “good” (<64%) filtering raw sugars, and insoluble starch was strongly correlated (R=-0.969) with filterability. A filterability index (FI) was determined using the filterability of water (FI=1.00) and increasing amounts soluble, swollen, and insoluble starch as references. An FI value of 0.59 was found to differentiate the filtering quality of raw sugars. The filterabilities of the two “poor” and two “good” raw sugars agreed with the FI=0.59 threshold and were attributable to their quantity of insoluble starch. Insoluble and swollen starches rapidly clogged filters, reduced filtration rates, and increased the viscosity of simulated melt liquors. In strong contrast, soluble starch did not affect melt liquor filterability and even facilitated it, most likely because of water structure interactions. Insoluble particle size correlated directly and strongly with filterability and was found to implicate the effects of larger macromolecular species included in raw sugars like colorants, dextran, and soluble starch on filtration rather than insoluble starch. Raw sugar filterability is complex and may not accurately reflect actual refinery performance without consideration of carbonatation clarification reactions. Among the parameters measured, total starch and insoluble starch are the most detrimental to raw and white sugar filterability; however, colour, invert, dextran, and ash may be indirectly involved. New refinery methods are urgently needed to accurately measure both soluble and insoluble starch content in raw sugars, to predict the filterability performance of raw sugars at the refinery. Further studies are needed to understand the roles soluble starch and insoluble starch has on the carbonatation reactions.