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ARS Home » Plains Area » Brookings, South Dakota » Integrated Cropping Systems Research » Research » Publications at this Location » Publication #211647
Title: Sorption Isotherm Characteristics of Dried Distillers Grains with Solubles (DDGS)

Author
item GANESAN, V - SOUTH DAKOTA STATE UNIV
item MUTHUKUMARAPPAN, K - SOUTH DAKOTA STATE UNIV
item Rosentrater, Kurt

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2008
Publication Date: 2/1/2008
Citation: Ganesan, V., Muthukumarappan, K., Rosentrater, K.A. 2008. Sorption Isotherm Characteristics of Dried Distillers Grains with Solubles (DDGS). Transactions of the ASABE. 51(1):169-176.

Interpretive Summary: Distillers Dried Grains with Solubles (DDGS), a coproduct of the fuel ethanol industry, is a highly nutritious animal feed ingredient. With the tremendous growth of the ethanol industry in the last several years, large quantities of distillers grains are now produced. To effectively utilize these feeds, these coproduct streams must be transported and then stored in various structures until final use. Unfortunately, DDGS flow can be problematic, as it often cakes and bridges during storage and transport, and thus cannot be unloaded. This issue may arise from a number of factors, including storage moisture, temperature, relative humidity, particle size, and time. The objective of this study was to quantify sorption isotherms for DDGS with varying soluble levels, in order to develop appropriate storage and transport information. Equilibrium moisture contents (EMC) of DDGS with four soluble levels (10, 15, 20, and 25% db) were determined at 10, 20, 30, and 40oC over four equilibrium relative humidity (ERH) levels (60, 70, 80, and 90%). EMC values for 10, 15, 20, and 25% (db) solubles ranged from 8.61 to 47.07% (db), 11.58 to 83.49% (db), 13.72 to 90.70% (db), and 15.03 to 132.01% (db), respectively. Nine models were then applied to fit the experimental data. The modified Halsey and modified Exponential models were found to perform well for the isotherm data. As there was no common model to predict sorption behavior for DDGS with various soluble levels, a new EMC model was developed. This new model, termed the GMR (Ganesan-Muthu-Rosentrater) model, incorporated soluble level in addition to temperature and moisture content. The GMR model (R2=0.94; F=977.55) produced the best fit for DDGS with varying soluble levels, and can be used to predict equilibrium moisture sorption behavior of DDGS.

Technical Abstract: Distillers Dried Grains with Solubles (DDGS) is widely recognized as a highly nutritious animal feed ingredient. With the exponential growth of the fuel ethanol industry in the past several years, significant quantities of distillers grains are now being produced. To effectively utilize these feeds in the domestic market, these coproduct streams have to be transported greater distances and must be stored in various structures until final use. Unfortunately, DDGS flow is often problematic as it frequently becomes restricted by caking and bridging during storage and transport. This issue may arise from a number of factors, including storage moisture, temperature, relative humidity, particle size, and time variations. The objective of this study was to develop sorption isotherms for DDGS with varying soluble levels, in order to provide facility designers and operators with appropriate storage and transport information. Equilibrium moisture contents (EMC) of DDGS with four different soluble levels (10, 15, 20, and 25% db) were determined using the static gravimetric method at 10, 20, 30, and 40oC over four equilibrium relative humidity (ERH) levels of 60, 70, 80, and 90%. The sorption capacity of DDGS increased with increasing temperature and soluble level, and followed a type III isotherm, which is commonly observed in high sugar foods. The observed EMC values for 10, 15, 20, and 25% (db) solubles ranged from 8.61 to 47.07% (db), 11.58 to 83.49% (db), 13.72 to 90.70% (db), and 15.03 to 132.01% (db), respectively. Nine models were then applied to fit the isotherm data. The modified Henderson and modified Chung-Pfost models did not fit the data, however, as the regression coefficients did not converge. The modified Halsey and modified Exponential models, on the other hand, were found to perform well for the isotherm data. As there was no common model to predict the sorption isotherms of DDGS with various soluble levels, a new EMC model was developed. This new model, termed the GMR (Ganesan-Muthu-Rosentrater) model, incorporated soluble level as one of the effects along with temperature and moisture content. The GMR model (R2=0.94; F=977.55), followed by a new modified Exponential 2 (NME2) model (R2=0.94; F=934.43), produced the best fits for DDGS with varying soluble levels, and can be used to predict equilibrium moisture sorption behavior of DDGS.