Location: Commodity Utilization Research2011 Annual Report
1a. Objectives (from AD-416)
The overall objective of this project is to enhance the value of sugarcane and sweet sorghum, and their major commercial products sugar and ethanol, respectively, by improving postharvest quality and processing. Develop markers of low quality harvested sugarcane and sweet sorghum to predict sugar factory/distillery processing. 1) Characterize and improve sugar industry process units to minimize the impact of sugarcane trash on factory performance, including sucrose losses. 2) Identify and develop commercially viable processing technologies for the production of very high pol (VHP) and very low color (VLC) raw sugars in sugar factories. 3) Improve postharvest processing of sweet sorghum and sugarcane for syrup and bioethanol production.
1b. Approach (from AD-416)
Undertake field and factory trials to characterize the affect of green sugarcane trash on processing and manufacture of VHP and VLC raw sugars. Undertake laboratory, pilot plant, and factory studies to reduce the negative impact of green trash impurities on industrial processing of sugarcane by improving process controls, designs, and the use of processing aids. Develop and deliver methods to sugarcane breeders and sugar processors that can be used to measure sugarcane quality indicator compounds, which in turn can predict future processing problems. Develop and deliver methods to sweet sorghum processors to predict processing problems and final bioethanol yields. Improve the harvesting and factory delivery protocol for sweet sorghum for the manufacture of syrup at existing sugarcane factories and the storage of sugarcane and sweet sorghum syrup for the manufacture of bioethanol.
3. Progress Report
Large studies were conducted at two sugarcane factories in Louisiana across the 2009 and 2010 processing seasons to measure sucrose (the main sugar in sugarcane and table sugar) losses. The results showed that most juice sucrose losses occurred in early season when sugarcane is less mature and there are more impurities that speed up the sucrose degradation reactions. The highest sucrose losses occur across the clarification and evaporation processes, where juice/syrup temperatures are high and the amount of soluble solids is low. Season average sucrose losses were 5.64 lbs sucrose lost per ton cane per day. We continued studies on seasonal and varietal effects on sugarcane juice quality parameters. For three commercial sugarcane varieties there was a strong varietal difference for starch and other parameters. From the results obtained it is now recommended that color controlling strategies at the factory and refinery should include a small removal of trash processed (which will also improve sucrose yields and profits). Sugarcane breeding programs should also include starch and color as selection criteria. The major (but not sole) contributor to sugarcane and sugar beet deterioration, particularly when warm and humid conditions prevail, is infection by Leuconostoc mesenteroides bacteria. Mannitol (a sugar alcohol) is a major product of deterioration that can predict processing problems. We previously developed an analytical method for mannitol in sugarcane juices. We were able to reduce the cost, and improve the precision and accuracy of the method. We showed that fructose (a sugar often found in sugar solutions) up to 18% did not interfere with the determination of mannitol. These results have been published. Dextranases (enzymes) are sometimes applied to break down dextran polysaccharide (a long chain sugar) in sugar manufacture when bacterial (mainly Leuconostoc) deterioration of sugarbeet has occurred. Work with collaborators on dextranase addition to raw juice has improved the clarification process at a sugarbeet factory. This resulted in increased throughput, reduction in process chemicals usage, improved operational stability, and reduced amount of water discharged to the site effluent treatment plant. This work has been published. Different harvesting and storage methods (i.e., whole stalk, short sections or billets of 20 or 40 cm, or shredded) were simulated to measure the stability of sugars in sweet sorghum and extent of deterioration. It was demonstrated that little sugar was lost over 4 days of storage when the sorghum was stored as whole stalks or billets, but significant sugar was lost within 24 hours if sorghum was shredded. The fastest and easiest way to tell that the sugar was deteriorating with storage was to measure the pH or titratable acidity of the juice. How to clarify sweet sorghum juice to produce sugar feedstocks for bioproducts was not known. We investigated the use of heat, lime, coagulants including proteins, and flocculants to produce clarified juice of acceptable quality. The use of flocculants and heating worked but coagulants did not.
1. Developed a new analytical method for mannitol. Routine mannitol determinations are necessary to define critical thresholds at each factory, as this affects how the factory processes a batch of sugarcane. ARS researchers in the Commodity Utilization Research Unit in New Orleans, Louisiana, developed a new analytical method for mannitol that can be used at the factory. The method became an Official International Commission for Uniform Methods in Sugar Analysis method GS8-12 “The Determination of Mannitol in Beet Juices, Thin Juices and Syrups by an Enzymatic Method.” With collaborators, we showed that mannitol measurements at a sugar beet factory allow (1) predicting and controlling processing problems (infections, clarification filterability, cleaning); (2) adapting anti-bacterial treatments during processing; and (3) undertaking process improvements (dead end pipes elimination etc.). All sugar beet factories in France are now measuring mannitol routinely, as well as factories in Belgium, Germany, Italy, and Poland. The method is also being tested in U.S. sugarbeet factories.
2. Determined the extent and location of factory sucrose losses across the sugarcane processing season. Sugarcane factory staff must consider all costs to make sound economic decisions on how to improve the performance of unit processes, which includes knowing the cost of sucrose losses across the factory and where they occur. ARS researchers in the Commodity Utilization Research Unit in New Orleans, Louisiana, showed that the majority of sugar loss is more likely early in the season and that it occurs in the clarification and evaporation processes. The estimated loss in a harvest season was 1.8 million dollars. The factory staff now know where and when to focus on reducing expensive losses.
3. Determined which harvest method should be used for sweet sorghum for the production of bioethanol. Sweet sorghum is currently harvested by various methods in the U.S., but how the methods affect deterioration and sugar content was unknown. ARS researchers in the Commodity Utilization Research Unit in New Orleans, Louisiana, showed that, when it came to sugar losses, it did not matter much whether the sorghum was stored for 4 days as whole stalks or billets. However, significant sugar was lost within 24 hours after harvest if sorghum was shredded. Growers now know that harvesting whole stalks or billets give adequate transport and storage time prior to processing for producing a feedstock for ethanol fermentation.
Zhou, M., Kimbeng, C., Edme, S., Hale, A., Viator, R., Eggleston, G. 2010. Sustainability of low starch concentrations in sugarcane through short-term optimized amylase and long-term breeding strategies. In: Eggleston, G., editor. Sustainability of the Sugar and Sugar-Ethanol Industries, ACS Symposium Series 1058. Washington, DC: American Chemical Society. p. 229-250.