Approaches to Raw Sugar Quality Improvement as a Route to

Chapter 12

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Approaches to Raw Sugar Quality Improvement as a Route to Sustaining a Reliable Supply of Purified Industrial Sugar Feedstocks John R. Vercellotti,*,1 Sharon V. Vercellotti,1 Gavin Kahn,2 and Gillian Eggleston3 1V-LABS,

INC., 423 N. Theard Street, Covington, LA 70433 Inc., 326 W. Lancaster Avenue, Ardmore, PA 19003 3Commodity Utilization Research Unit, Southern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, New Orleans, LA 70124 *[email protected] 2Carbochem,

Energy costs in the sugar industry are outstrippling costs of manufacture, particularly in refineries. This, as well as increasing transportation costs and the need to meet manufacturers’ tight specifications, has increased the demand for a sustainable supply of purified, raw sugar. Agricultural commodity delivery of purified, raw sugar as an adequately refined raw material for manufacturing value-added products demands consistently high quality to to be competitive. To achieve very low colorant and high pol values in purified, raw sugars, components in raw juice inhibiting the crystallization of sugar must be identified. Micro- and nanoparticulate materials can foul sensitive surface properties of adsorbents such as powdered activated carbons (PACs) or resins. Improved approaches to clarification, such as combined centrifugation, microfiltration or nanofiltration of sugar juices or syrups permit more efficient decolorizing with solid adsorbents. Lower quality sugars can thus be upgraded to permit isolation of product while sustaining energy utilization.

© 2010 American Chemical Society

Introduction


“Sustain” is derived in the English language from the Latin word sustinere, the sus- prefix (from the preposition sub) meaning “from below” and the verb tenere, “to hold” (1). John Ikerd, Professor Emeritus of Agricultural Economics, University of Missouri, Columbia, often used this equation to account for distributive confluence of sustainability (2):

where I = Environmental impact, P = Population, A = Affluence, T = Technology. At the early part of the last century a typical quarter section, 160 acre family farm in northern Illinois survived because certain energy and investment inputs could be balanced. Although this report is about purified raw sugar production from sugarcane, calculations about corn yield and total investment input one hundred years ago still hold. It then took about 85 gallons (322 liters) of gasoline to produce a harvested acre of corn. This takes a lot of inputs into account such as the cost of plowing or harvesting machinery, drying, fertilizer application, and tilling. Even at a high yield of 200 bushels of corn per acre, at US$4.00 per bushel today that is a sale price of $800 per acre. With gasoline today at about $2.50 per gallon, the fuel alone costs $212.50 or one-fourth the sale price of the corn. Furthermore, this does not account for the hybrid seed costs, pesticide use, special fertilizers, tax structure, labor per hour, depreciation or maintenance of equipment, and fluctuations in the grain markets (3, 4). A similar calculation with respect to sugarcane from field to final raw sugar is as complex.

Economic Significance of Raw Sugar for Sustaining the Future of the Sugar Industry Current world demand for high quality sucrose-based sweeteners is very great. Raw sugar, as recorded on the current and extensive U.S.D.A.-E.R.S. survey tables, is very heterogeneous with respect to quality (5). With the rising costs of energy, raw sugar manufacturing costs reflect a tightening market demand for raw sugar. World raw sugar prices in January and February, 2010, were 28.94 and 27.29 US cents/lb and March 16, 19.33 cents/lb. In the commercial sweetener industries, the use of high fructose corn syrup (HFCS) use has been steadily falling according to the U.S.D.A.-E.R.S. as well as the Corn Refiners Association, due to consumer concerns and preferences. Values of HFCS reduction have ranged between 13-17% less since 2001 (5). Sucrose based sweeteners, including purified, raw sugars are meeting consumer preference demands and have contributed considerably to the world-wide increase of raw sugar remelting. There is no such thing as a “reagent grade raw sugar.” Although demand for purified, raw sugar is increasing, energy costs for a sustainable level of this product outstrips cost of manufacturing in many areas of the world. Agricultural commodity delivery of sugar as an adequately refined raw material for manufacturing value-added products demands that the highest quality yields of purified, raw sugar be realized to be competitive. Lower quality sugars can 192


thus be upgraded to permit isolation of acceptable products while sustaining more favorable energy utilization. Since such large amounts of energy and labor are already expended on the manufacture of raw sugars, salvaging useful final products for use in high end sweetener applications makes a lot of sense. Marginal raw sugars for remelting processes have not only high International Commission for Uniform Methods of Sugar Analysis (ICUMSA) specified color (IU) values but also considerable turbidity values because of the presence of both sediment and colloidal particulate (6, 7). Various strategies must be employed to achieve high pol, low ICUMSA color (less than 50 IU), with low invert sugar, turbidity, dextran or polysaccharides, 5-hydroxymethylfurfural, ash, especially iron salts, little olfactory off-flavors that could prejudice a high end product’s flavor quality, and absence of pesticide residues, mycotoxins, polluting chemicals, and polyphenolic color compounds (8–10). The objective of this work was to compare the quality of raw sugar samples from various countries where they are utilized by carbonated beverage and other high end manufacturers after they have been remelted, clarified, and decolorized with powdered activated carbon (PAC) and finally polished with nanofiltration. In countries where final refining of raw sugar into white, refined sugar is not economically feasible, practical utilization of purified, raw sugars, that are borderline for higher end use, can be made at cost savings.

Effective Powdered Activated Carbons (PACs) for Decolorization of Raw Sugars Critical to this work has been the identification of PACs that can survive applied loads of raw sugars containing large amounts of impurities, i.e., with turbidity in ≥ 600 ICUMSA Unit (IU), which can deactivate the carbon by fouling. We have examined hundreds of raw sugars from world-wide markets that represent many types and ranges of impurities. The following examples make the point that further utilization of such purified, raw sugars can increase energy savings from the expensive refining of raw sugar into white sugar and, thus, contribute to a more sustainable sugar production. There are two key issues involved in the ability of PAC to treat high color raw sugars: the higher PAC dose rates required to achieve a final color < 50 IU, for example, and the corresponding filtration issues which relate to the loading capacity of the typical filters in industrial use today (11, 12). Carbochem® CA-50 powdered activated carbon (source: wood, chemically activated) was used in these studies as a wide range sugar decolorizer due to its high decolorizing efficiency and particle size distribution which minimize the filtration limitations. The particle sizes range from 1 - 45 µm diameter which eliminates the fines fraction defined as particles 0.2%>0.1% wt/wt (Figure 4). In Figure 5, the 8 µm pore size prefiltration step, which removes larger particles from the unfiltered raw sugar, permitted the PAC to remove more colorant than from the unfiltered raw sugar syrup shown in Figure 4. With this 8 µm filtration step the same color reduction was achieved with 0.2% PAC as was done with 0.3% PAC alone in Figure 4. The 1.6 µm spun glass filter permitted even more effective removal of the colorant with PAC as more microparticulate was removed by the filter than with the 8 µm filter (Figure 6). The PAC was most effective after the 60 Brix syrup was prefiltered with the tightest membrane (Figure 7). The 0.45 µm Nylon membrane removed not only all of the microparticulate but also a large share of nanoparticles. These nano-range colloidal suspensions no longer enter into the pores of carbon particles and mask over large areas of decolorizing surface; thus, the colorant was most efficiently adsorbed.

Laser Light Scattering Particulate Analyses of Raw Sugars Ten representative international raw sugars and associated sediments, were analyzed for particulate distribution by multiple angle laser light scattering analysis. Light scattering particle size distribution of sediment and particulate in raw sugars was undertaken to further compare the compositions of the raw sugars studied. The broad range of particle sizes did not permit the inclusion of all the percentages for the range of particle sizes. Figure 8 displays a cross-section of one of the typical Mexican raw sugars in this study. Each sugar from the various factories is different having its own specific profile. The range of particle sizes from nanoparticulate to higher micrometer diameters is relevant to the mechanisms of fouling of the activated carbon pores and adsorbent surfaces. There are strong arguments for pretreatment of raw sugars before application of further decolorizing processes. This pretreatment could remove nanoparticulate which fouls PAC as well as clogs necessary filter media for clarification and decolorizing. The sample in Figure 8 is diagnostic of the particle interferences to PAC treatment during processing.

Future Developments in the Upgrading of Raw Sugars for Remelting Practical application of the knowledge gained in this laboratory study to the industrial scale involves many of the same factors. The carbon used in the present studies, Carbochem® CA-50 PAC, has been very successfully used world-wide without need of prior industrial micro- or nanofiltration (23). Industrial reports of recent factory trials using Carbochem® CA-50 PAC on raw sugar samples within reasonable turbidities and colors, 600 IU or less (23), suggest that multiple ton quantities of raw sugar can be remelted to very pure, high quality product. Previous reports of processes for refining raw cane sugar in 203


a remelting operation (21) have depended on initial clarification with tangential microfiltration and resin demineralization followed by PAC treatment. In the 1990’s trials were held (17–19, 22) to evaluate on-line disk stack centrifugation as an advanced clarification process to eliminate micro- and nanoparticulate. Not only were greater yields of crystallization found, but the raw sugars contained much less microparticulate or colloidally stable polymers. More recently the Brazilian firm, Mecat Filtracoes Industrias (Golas, Brazil) has developed very efficient continuous centrifugal clarification of raw sugar syrups (MECAT Turbo [centrifugal] Filters™) (24). This new technology used in both Brazilian sugar and food processing industries has resulted in highly reliable centrifugal nano- or microfiltration. Such equipment is capable of handling heavy loads of sediments which prevent easy decolorizing in raw sugar. The MECAT Turbo Filter™ does not remove colorant, but as a prefilter removes all of the turbid sediment (24). Consequently, this pretreatment permits more effective PAC treatment as demonstrated above in the membrane prefiltrations before PAC treatment.

Conclusions Agricultural commodity delivery of sugar as an adequately refined material for manufacturing value-added products demands high yields of purified, raw sugar, if it is to be realistically competitive. Demand for purified, raw sugar is increasing because of expensive energy costs for refined white sugar production. Micro- and nanoparticulate can foul sensitive surface properties of adsorbents such as PACs or resins. Components in raw juice inhibiting the decolorizing of sugar must be removed to achieve very low colorant and high pol values. Development of improved powdered activated carbons with particle size limits, as well as optimal porosity, greatly increases resistance to fouling from turbid particles in raw sugars. At the same time elimination of excess particle fines enhances filterability of treated syrups. Commercial PACs such as Carbochem® CA-50 can achieve these goals and effectively removes a wide spectrum of colorant. Improved clarification processes currently being developed, such as centrifugation/ microfiltration or nanofiltration of sugar juices or syrups, will permit more efficient decolorizing with such an adsorbent that optimizes decolorizing performance and filtration properties.

Acknowledgments The authors wish to express their thanks to Mr. Eldwin St. Cyr of the USDA-ARS, Southern Regional Research Center in New Orleans LA, for his contributions to particle size analysis of raw sugars. The generous assistance of Mrs. Susan Eleew of V-LABS, INC., Covington LA, has been very valuable in bringing this manuscript to completion, for which the authors are most grateful. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. 204

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