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United States Department of Agriculture

Agricultural Research Service

Research Project: Postharvest Quality and Processing of Sugarcane and Sweet Sorghum for Sugar and Ethanol Production

Location: Commodity Utilization Research

2013 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:
Determined the extent and location of sucrose losses in a factory 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 sucrose 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 is 1.8 million dollars. The factory staff now know where and when to focus on reducing expensive losses. Large sugarcane factory studies across two Louisiana processing seasons were completed to determine how lime saccharate (solubilized lime in hot juice) and traditional milk of lime (lime suspended in warm water) controlled pH and affected the hot lime clarification process. Overall, lime saccharate provided better turbidity values and control for clarified juices because of better removal of microscopic particles, increased target pHs, and significantly reduced expensive sucrose losses especially when the sugarcane delivered to the factory was at its lowest value in early season. At least two factories have now changed to lime saccharate addition. Large studies across two Louisiana processing seasons were completed to ascertain the effects of harvest date and variety on sugarcane juice quality parameters as they affect high quality raw sugars for supply to refineries. The maturity characteristic of the variety played a critical role in seasonal variation of quality parameters, especially starch. Later maturing varieties deliver relatively higher amounts of starch across the whole season and have contributed to the much higher levels of starch being delivered to Louisiana sugar factories in recent years. Overall, for all parameters studied the type of tissue had the strongest effect, followed by variety, then date of harvest; the varietal effect was greatest in the stalk than other tissues. This strongly suggests that breeding programs could include quality parameters as selection criteria. In collaboration with scientists from ARS-USDA-Houma, Louisiana we showed that forage harvesting of sweet sorghum into shredded stalks creates too much deterioration and loss of fermentable sugars between industrial cut-to-crush times. Current recommendations to sweet sorghum growers in the Mississippi Delta Region are 8 inch billets (short pieces of stalk). How clarification of sweet sorghum juice affects the quality of syrups was not known. In new studies, we investigated the use of heat, lime, coagulants including proteins, and flocculants to produce clarified juice which was then evaporated under vacuum into syrup. Juice clarification greatly improved the quality of syrup and amount of fermentable sugars produced. A strong sweet sorghum cultivar effect was discovered for juice quality, clarification performance, and clarified juice quality.

4. Accomplishments
1. Pilot-scale processing to stabilize sweet sorghum juice and syrup. A method was developed for the stabilization and clarification of juice for long-term storage, year-round supply, and efficient transport. ARS scientists from the Commodity Utilization Unit of the Southern Regional Research Center in New Orleans, LA, with industrial collaborators at BioDimensions Delta BioRenewables, Memphis, TN, further validated a developed industrial sweet sorghum clarification method at the pilot plant scale. Clarification did not impede fermentation and had the added advantage of juice and syrup stabilization and better storage of syrups. It was also found that inexpensive surface treatments including soybean oil and candelilla wax showed strong potential to prevent microbial contamination of syrups which are easier to handle and transport. The results impact the commercial, large-scale manufacture of biofuels and bioproducts from sweet sorghum by allowing long-term storage and transportation without sugar degradation.

2. Method for detecting soluble and insoluble starch in sugarcane juice. In recent years, starch impurity concentrations in sugarcane have been increasing in the United States. Previously, it was considered that factory syrups contained only soluble starch, but ARS scientists from the Commodity Utilization Unit of the Southern Regional Research Center in New Orleans, LA, discovered up to 65% insoluble (granular) starch in syrups from a Louisiana factory using both microscopic and chemical techniques. Insoluble starch was also found in some raw sugars, particularly those with high soluble starch content. A research method was also developed to accurately measure both insoluble and soluble starch in sugarcane products, based on sound waves. This will be critical in finding industrial solutions to the profound detrimental effects on insoluble starch on amylase (catalyst used to break down starch) applications and sugar yields.

3. Microbial contamination reduced in sweet sorghum juice. Sweet sorghum is currently harvested by various methods in the U.S., but how the methods affect deterioration was unknown. Initial analyses of a sweet sorghum deterioration study indicated that, across four commercial cultivars, sodium carbamate biocide (chemical that kills microbes) reduced but did not eliminate microbial contamination. More than a dozen potentially unique microbial species were observed in the processed juice, and have been propagated for individual identification. Sweet sorghum cultivars showed fewer microbes in the 4 than 8 inch long billet stalks. The increase in cut surface area of the shorter billets allowed the microbial population to be higher than for the larger billets. However, it was also demonstrated that the juice from the shorter billets were more acidic, which could limit survivability of microbes, in particular survivability of bacteria. This knowledge will benefit growers and processors in how to control sweet sorghum deterioration.

Review Publications
Andrzejewski, B., Eggleston, G., Lingle, S., Powell, R. 2013. Development of a sweet sorghum juice clarification method in the manufacture of industrial feedstocks for value-added products. Industrial Crops and Products. 44:77-87.

Lingle, S.E., Tew, T.L., Rukavina, H., Boykin, D.L. 2013. Post-harvest changes in sweet sorghum II: pH, acidity, protein, starch, and mannitol. BioEnergy Research. 6(1):178-187.

Eggleston, G., Viator, R., Gateuil, A., Fenger, J-A., White, P., Jackson, W., Waguespack, Jr, H., Blackwelder, N. 2013. Effects of seasonal variations of sugarcane stalk and extraneous matter quantity and quality as they affect recoverable sugar, starch, and fiber: Part 1. International Sugar Journal. 115(1375):477-487.

Eggleston, G., Gober, J., St Cyr, E. 2013. Development of an industrial method to quantitatively measure carry-over amylase activity in raw and refined sugars. International Sugar Journal. 115(1370):123-131.

Andrzejewski, B., Eggleston, G., Powell, R. 2013. Pilot plant clarification of sweet sorghum juice and evaporation of raw and clarified juices. Industrial Crops and Products. 49:648-658.

Eggleston, G., Cole, M., Andrzejewski, B. 2013. New commercially viable processing technologies for the production of sugar feedstocks from sweet sorghum (Sorghum bicolor L. Moench) for manufacture of biofuels and bioproducts. Sugar Tech. 15(3):232-249.

Eggleston, G., Tew, T., Panella, L., Klasson, T. 2010. Ethanol from Sugar Crops. In: Singh, B.P., editor. Industrial Crops and Uses. Wallingford, United Kingdom:CABI (Council of Applied Biology International). Chapter 3, p. 60-83.

Last Modified: 05/27/2017
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